SAIP2025

Jul 7, 2025, 7:00 AM → Jul 11, 2025, 11:20 PM Africa/Johannesburg

Solomon Mahlangu House (University of the Witwatersrand, Johannesburg)

Philippe Ferrer (Wits)

REGISTRATION EXTENDED -> 23rd May!

Mon, July 7

Council Meeting

Winter School: Advances in Condensed Matter and Materials Physics

Winter School: Applications of Machine Learning in Particle Physics

Winter School: Celebrating our quantum past, and embracing its future

Winter School: Hands-on heavy-ion physics with the ALICE detector

Winter School: Introduction to Lattice Field Theory

10:20 AM Morning Tea

Winter School: Advances in Condensed Matter and Materials Physics

Winter School: Applications of Machine Learning in Particle Physics

Winter School: Celebrating our quantum past, and embracing its future

Winter School: Hands-on heavy-ion physics with the ALICE detector

Winter School: Introduction to Lattice Field Theory

12:30 PM Breather

12:35 PM Lunch

1:45 PM Breather

Winter School: Advances in Condensed Matter and Materials Physics

Winter School: Applications of Machine Learning in Particle Physics

Winter School: Celebrating our quantum past, and embracing its future

Winter School: Hands-on heavy-ion physics with the ALICE detector

Winter School: Introduction to Lattice Field Theory

3:40 PM Afternoon Tea

Winter School: Advances in Condensed Matter and Materials Physics

Winter School: Applications of Machine Learning in Particle Physics

Winter School: Celebrating our quantum past, and embracing its future

Winter School: Hands-on heavy-ion physics with the ALICE detector

Winter School: Introduction to Lattice Field Theory

Welcome function

Tue, July 8

Plenary

9:15 AM Breather

Applied Physics

Convener: Alan Matthews

1 Synopsis of the prototype parabolic trough

The 20kW prototype parabolic trough was completed and the novel receiver performance measured in a realistic setting, completing a project that has led to this point over many years. The final analysis veers away from the original theoretical description, using a more conventional approach and detailed thermal network, necessitated by the insufficient vacuum levels obtained during testing. We fit the new theoretical description to the data, approximating parameters for both the cooling and heating regime, and extrapolate the performance of a similar system with added insulation instead of an evacuated annulus.

Speaker: Philippe Ferrer (Wits)

2 Modulating properties of solid carbon nanospheres via ion implantation with hetero-ions

Solid carbon nanospheres of ~200 nm diameter have been prepared and then doped by ion implantation, using a specialized end-station adapted for the uniform implantation of powders. Boron, nitrogen and neon ions were chosen initially, the latter for control purposes. Herein, the dependence of the physicochemical properties of solid carbon spheres on the fluence of the implanted ions was investigated by controlling the dosage of the 100 keV of B+, N+ and Ne+ ions into the carbon shell over 7 h and 14 h implantation periods at room temperature. SEM analysis revealed significant surface deformation in the form of cracks for the Ne+ implanted samples, whilst little structural deformation was observed when N+ and B+ implanted samples. Furthermore, TEM micrographs confirmed dependence of the structural properties on the ion fluence, as shown by formation of varying thickness of an amorphous carbon layer after implantation with B+, N+ and Ne+ ions, respectively. Finally, magnetic properties showed that the type of the hetero-ion as well as the affiliation of the carbon to the hetero-ion influenced the transition from diamagnetism to super-paramagnetism. The Néel temperature varied somewhat but was below about 10 K. Boron conferred a much greater paramagnetic susceptibility at low temperature than the other ions, and showed indications of a higher electrical conductivity at higher temperatures, suggesting an electronic doping effect. The study showed the importance of the choice of the heteroatom ion on the properties of the solid carbon spheres for the development of next generation carbon-based electronic devices.

Speaker: Trevor Derry

3 Transforming Coherent Telecom Receivers into Current Sensors

Lightning-induced damage poses a major threat to infrastructure, particularly in power and telecommunications networks. Accurate current measurements are essential for designing protective systems and assessing damage. While traditional sensors such as shunt resistors and Rogowski coils offer high accuracy, they must be installed at the strike point, making them unsuitable for wide-area deployment. Remote sensing approaches can scale across many installations; however, current estimates derived from measured fields and empirical models limit their accuracy. Achieving the precision of local measurements through remote means remains an open challenge. This research explores a novel method for distributed lightning current measurement using deployed fibre telecom infrastructure.

Lightning-induced magnetic fields cause polarisation changes in the light transmitted through optical fibre via the Faraday effect. By monitoring these changes, both fast and slow current measurements can be made. In contrast, many existing lightning current measurement techniques struggle to detect slow changes due to their reliance on measuring the time derivative of the current or field. Coherent optical receivers in telecom systems already track polarisation changes to compensate for environmental effects that alter the transmitted optical signal. This raises an important question: can polarisation information from these receivers be repurposed for lightning current sensing?

This study investigates the feasibility of using polarisation data from coherent receivers for current measurement. We experimentally compare this approach with a standard fibre optic current sensor, assessing its ability to measure fast- and slow-changing currents. Performance is evaluated in terms of linearity, resolution, sensitivity, and noise immunity, laying the groundwork for scalable lightning current measurement using deployed optical networks.

Speaker: Alice Drozdov (University of the Witwatersrand)

Astrophysics & Space Science: Space Science Session 1

Convener: Ruhann Steyn (Centre for Space Research, North-West University)

4 Update on the air quality dashboard development

The climate crisis persists, as the global community has yet to fully embrace the actions needed
to tackle it. The decade from 2010 to 2019 was the hottest on record, leading to devastating wildfires,
hurricanes, droughts, floods, and other climate-related disasters worldwide. To limit global
warming to 1.5℃ above pre-industrial levels, emissions must already be on the decline and need to
be halved by 2030. Unfortunately, we are far from meeting this target. Sustainable Development
Goal 13 emphasizes the need for urgent climate action, pointing to the rising global temperatures
and increased air pollution that pose significant threats to human health. This highlights the importance
of emission monitoring. In South Africa, however, emission data remains a challenge,
making satellite data especially valuable. Satellites are increasingly used to monitor air quality
and track atmospheric pollution. Around the world, studies are using data from the Tropospheric
Monitoring Instrument (TROPOMI) to assess emissions and air quality. However, no air quality
dashboard based on satellite data has been developed in South Africa using TROPOMI-Sentinel
5p data. This project aims to compute the Air Quality Index (AQI) using the Google Earth Engine
(GEE) platform. Sulphur dioxide (SO2), nitrogen dioxide (NO2), and carbon monoxide (CO) will be
the first pollutants used to calculate the AQI. A functional dashboard will be created to offer users
easy access to standardised satellite data, enabling quick and effortless analysis.

Speaker: Lerato Shikwambana (South African National Space Agency)

5 Simultaneous multiple conjugate nighttime MSTIDs observations: 4 October 2018

This study reports on nighttime medium-scale traveling ionospheric disturbances (MSTIDs) observed
by conjugate midlatitude all-sky imagers in Sutherland (32.4◦S, 20.8◦E; magnetic latitude:
∼-40.9◦) and Asiago (45.87◦N, 11.53◦E; magnetic latitude: ∼40.3◦) on the 4th of October 2018. These
MSTIDs had fronts elongated along the northeast-southwest (NE-SW) and northwest-southeast
(NW-SE) directions in the Southern and Northern Hemispheres. The NE-SW aligned MSTIDs propagated
in the NW (SE) direction in the Southern (Northern) Hemisphere, while the NW-SE aligned
MSTIDs propagated in the NE (SW) direction in the Southern (Northern) Hemisphere. This study
reports the first optical observations of conjugate NE-SW/NW-SE aligned and equator-eastward
propagating MSTIDs. These MSTIDs are possibly linked to gravity wave-induced polarization
electric field in the Northern Hemisphere, as significant gravity wave activity in the mesosphere
was detected from the OH and OI greenline observations by the Asiago imager, and mapped to
the Southern Hemisphere. Their equator-eastward propagation direction was favoured by background
winds at the hemisphere of origin, which were determined from a global model and observations.
The NE-SW/NW-SE aligned and equator-westward propagating MSTIDs were likely
generated through the coupled Perkins and sporadic E instabilities, since they were observed in
the presence of sporadic E layers and with reasonable Perkins instability growth rates. Polarization
electric fields induced by the observed gravity waves and sporadic E layers resulted in two
pairs of conjugate MSTIDs.

Speaker: Zama Katamzi-Joseph

6 Investigating the influence of Boundary Layer Dynamics on Aerosol Optical Properties Using Ceilometer and Cimel Sun Photometer

Monitoring atmospheric conditions is crucial for understanding the behaviour of aerosols, which
directly impact air quality, climate, and satellite-based remote sensing applications. In this study,
we focus on the atmospheric boundary layer (ABL), which regulates the dispersion, transport,
and transformation of aerosols. Ceilometers, which measure the height of the boundary layer
by detecting the backscatter of laser pulses, are used to observe ABL dynamics, including variations
in boundary layer height (BLH), aerosol stratification, and vertical mixing. The Cimel Sun
Photometer, a ground-based instrument that measures aerosol optical depth (AOD) and radiative
properties of aerosols through direct sunlight measurements, is employed to provide insights into
columnar aerosol loading, size distribution, and optical properties. This study examines the correlation
between ABL height, as measured by the ceilometer, and AOD trends from the Cimel
Sun Photometer over Pretoria, a region with high pollution sources such as industrial areas and
significant seasonal changes. By integrating these datasets, we assess how fluctuations in BLH
influence aerosol concentration and optical properties across different seasons (summer, autumn,
and winter). This research contributes to improving air quality assessments, validating aerosol
models, and enhancing the parameterisation of aerosol dynamics in climate models

Speaker: Zimbini Faniso-Mnyaka (CSIR)

Nuclear, Particle and Radiation Physics-1

7 Linear polarization measurement on gamma rays from non-oriented nuclear states

Author : Beatrice Similindi
Co-author : Dr E.A Lawrie
Dr S.N.T Majola

Gamma ray spectroscopy is a powerful tool in nuclear structure, but the interpretation of the intrinsic properties of the nucleus becomes complex if the parity of the emitted radiation is not known. This study aimed at developing a technique to measure linear polarization of ɣ rays emitted
from non-oriented nuclear states for the clover detectors of the iThemba LABS AFRODITE and GAMKA arrays. Orientation was created by gating on a γ ray detected in one clover detector while observing another γ ray detected in coincidence in another detector. Having being well known for
their high efficiency in detecting γ rays, the clover detectors used in this study comprise 4 Ge crystals which were used as Compton polarimeter, which allows us to measure linear polarization. A focus was made on studying the Compton scattering of γ rays across the 4 Ge crystals in which the Klein-Nishina equation was utilised for the two experimental set-ups to measure the polarization anisotropy. Theoretical curves for all observed rays emitted from the beta-decay of 152 Eu were derived and compared with the measured polarization anisotropy, Ap to deduce the polarization sensitivity, Q(γ). Furthermore, the degree of linear polarization was determined experimentally for the γ rays observed in 196Hg following the beta-decay of 196Tl using the deduced polarization sensitivity for the AFRODITE array. The technique has also been applied
for the upgraded GAMKA array. The polarization sensitivity for the GAMKA array was determined using experimental data with Eu source by measuring the linear polarization anisotropy and comparing it with the theoretical curves for linear polarization for the well-known pure transitions.
The derived linear polarization sensitivity Q was then used to determine mixing ratios of observed mixed transitions. In addition, the angular correlation coefficients for both pure and mixed transition have been measured and compared with the theoretical coefficients. Lastly, final values for the mixing ratios for M1+E2 and E0+M1+E2 transitions have been determined by combining angular correlation and linear polarization results for all observed γ ray cascades detected with the GAMKA
array and with Eu source. The deduced polarization sensitivity can be used in future experiments that intend to measure ɣ rays whose parities as well as mixing ratios are not known.

[1] K. Krane, Introductory Nuclear Physics, chapters 7.1 (Electro Magnetic Radiation), 7.9 (Polarimeters), 10.1, 10.2, (optional 10.3), 10.4, 10.5.
[2] G. Duchene et al., Nucl. Instrum. Meth. A, 432, 90 (1999).
[3] Fagg, L. W. and Hanna, S. S. Polarization measurements on nuclear γ- rays. Reviews of Modern Physics, 31(3):711, 1959.
[4] P. Jones et al., Nucl. Instrum. Meth. A, 362, 556 (1995).
[5] A. Wolf et al., Phys. Rev. C 66, 024323 (2002).

Speaker: Ms Beatrice Similindi (iThemba LABS)

8 Systematics study of octupole bands in rotating even-even nuclei to reveal rigid or soft octupole shape

The systematic study of octupole bands in rotating even-even nuclei has gained interest in understanding features of the octupole deformation, including octupole rigidity and softness. Furthermore, one could study how nuclear rotation influences this rigidity or softness and how experimental data from gamma-ray spectroscopy aligns with theoretical predictions for octupole deformation. Nuclear with octupole shape resembles the shape of a pear. They show pairs of alternating parity bands, providing evidence of octupole correlation that influences macroscopic and collective features of nuclear matter and fundamental nuclear properties. Rotation is a distinct motion in both classical and quantum mechanics. Assuming a constant moment of inertia, the excitation energy is proportional to the square of the angular momentum operator, and the gamma-ray energies are directly proportional to the angular momentum, I, and inversely proportional to the moment of inertia, J. Moreover, nuclei can show both quadrupole and octupole deformations, a property often seen in heavy nuclei within the A ≈ 240 mass region. The presence of ground-state bands and their associated 3-octupole bands indicates the existence of octupole correlations. At present, researchers often apply the alignments analysis to identify whether a nucleus maintains a rigid octupole shape or displays octupole softness, (octupole vibration). This alignment analysis relies on input dependent parameters like Harris parameters, which introduces limitations in understanding nuclear shapes clearly. To overcome this, a new Coriolis technique is introduced, offering a parameter-free approach to analyze experimental data obtained from the National Nuclear Data Center (NNDC). This analysis represents a technique to study octupole deformations across different isotopes and compare results with existing techniques. Such Coriolis analysis is used to identify whether a nucleus has a rigid octupole shape or a soft octupole shape (vibration).

keywords: Octupole deformation, Gamma-ray, Coriolis technique, Rigid octupole & Soft octupole

Speaker: Muzomuhle Muzomuhle

9 Electromagnetic and thermodynamic properties in the quasi-continuum of mid-mass nuclei through inverse and direct kinematics.

The electromagnetic properties of nuclei excited to the quasi-continuum region are best studied and explained using statistical decay observables, such as the nuclear level density (NLD) and γ-ray strength function (γSF). These quantities can be extracted from experimental particle-γ coincidence matrix using the Oslo method and Shape method, respectively. In this study, experiments were carried out at iThemba LABS using the AFRODITE array with $^{84}$Kr beam on a deuterated polyethylene target, and proton beam on $^{64}$Ni target to undergo (d, p) reactions, producing 85Kr and $^{63}$Ni. The nuclear level density and strength function will be extracted from the coincidence events which were detected in the AFRODITE array. The NLD and γSF will be investigated to i) determine the existence of low-lying energy enhancement in $^{85}$Kr, confirm the reported of low-lying energy enhancement in $^{63}$Ni ii) perform a rigorous test of the Brink-Axel hypothesis in $^{85}$Kr and $^{63}$Ni, and iii) the first experimental determination of thermodynamic properties of $^{85}$Kr and $^{63}$Ni.

Speaker: Mhlangano Freedom Nkalanga (University of Johannesburg)

10 Detecting Anomalies in Measured Thermal Neutron Flux Profiles of SAFARI-1 Research Reactor.

The accurate measurement, analysis, and correct interpretation of the neutron flux distribution within the reactor core are essential for reactor safety, optimum performance, and understanding of reactor operations. In the SAFARI-1 research reactor, axial thermal neutron flux profiles of fuel-containing assemblies are measured at the beginning of each operational cycle by activating natural copper wires. This study investigates the variation in measured flux profiles by considering the movement of the control rod bank and copper wire axial positioning. The analysis is focused on the key features of the neutron flux profile: the bottom minimum, peak maximum, and top minimum and their axial location, with the goal of using this information to identify inadvertently axially shifted measurements. The research approach involved data preprocessing, visualization, and statistical analysis. The analysis produced 1D, 2D, and 3D flux representations, which can be related to the control rod bank movement, axial wire insertion in the fuel-containing assemblies, and fuel assembly position. A polynomial fit was applied to estimate the location of the flux profile's key features, and the distribution of these points as well as their correlation to bank positions were analysed. The standard deviation along with the Median Absolute Deviation and Pearson's Correlation Coefficient were used to characterize the sensitivity of the flux profiles to control bank positions. Results of the study show that peak maximum points exhibit higher variability and a stronger positive correlation to the bank positions than the bottom and top minimum points. The bottom minimum points have lower variability and are less correlated to the bank positions. However, this is due to some points missing in this case, causing inconsistency and biased results. The top minimum points remain consistent and positively correlate to the bank positions and may thereby be the most suited for the measurement shift characterization. This study's findings demonstrate the effectiveness of the proposed approach in identifying and correcting the shift in flux profile measurements resulting from improper copper wire insertion. The study ensures a more accurate interpretation of neutron flux profiles by distinguishing the actual variations from apparent anomalies.

Speaker: Rethabile Kgolobe

11 Effect of SrO on radiation attenuation properties of boro-tellurate glass systems at a high energy region.

In this study the effect of radiation ionization of the 40SrO–30B2O$_{3}$–10TeO$_2$–20Bi$_2$O3, 35SrO–30B$_2$O$_3$–10TeO$_2$–25Bi2O$_3$, 30SrO–30B$_2$O$_3$–10TeO$_2$–30Bi$_2$O$_3$, 25SrO–30B$_2$O$_3$–10TeO$_2$ 35Bi$_2$O$_3$, 20SrO–30B$_2$O$_3$–10TeOS$_2$–40Bi$_2$O$_3$ glass was investigated using the Phy-X/PSD, XCOM simulation Software and ratified using the geant4 simulation. Between the high energy region between 1 MeV and 15 MeV, the mass attenuation coefficients (MAC), linear attenuation coefficient (LAC), and Effective atomic number of all the glasses under investigation were calculated. The results show that increasing the concentration of Bi$_2$O$_3$ in these glasses improves its radiation shielding ability. The half value layer (HVL), tenth value layer (TVL) and mean free path (MFP) of the glass were investigated and the results show that glasses with a high concentration of Bi$_2$O$_3$ attenuated high amount of photons at a smaller thickness. It was also observed 20SrO 30B$_2$O$_3$–10TeOS$_2$–40Bi$_2$O$_3$ glass has better radiation shielding compared to other radiation shielding materials that have been investigated.

Speaker: Mr Sifiso Mthalane (University of Zululand)

12 RADIOLOGICAL RISKS ASSESSMENT OF MINING VICINITIES USING RESRAD COMPUTER CODE

Environmental radioactivity monitoring and protection often require measurement and modelling of natural radionuclides in environmental media and exposure pathways. In this study, the activity concentration of natural radionuclides determined using Broad energy germanium detector, was used to model the radiological risks for a hypothetical resident using Residual Radioactivity (RESRAD) computer code. The activity concentration of K-40, Th-232 and U-238 of soil sampled in Rustenburg mining vicinities was found to be less than global average values of 400 Bq/kg, 35 Bq/kg and 30 Bq/kg reported by the United Nations Scientific Committee on the Effects of Atomic Radiation respectively. The maximum total effective dose and excess life cancer risk estimated using RESRAD-offsite code in investigated area are 0.5190 mSv/yr at year 16.92 and 8.58 at year 0, respectively. Total excess life cancer risk is observed to be below 2.90 × 10-4, along with the total effective dose which is also lower than 1 mSv/yr reported by UNSCEAR (2000). Thus, the study reveals insignificant radiological hazards in investigated mining vicinities. However, regular environmental measurement and monitoring is recommended to ensure resident exposure is as low as reasonably achievable.

Speaker: Dr Peter Oluwadamilare Olagbaju (Physics Department, North-West University, South Africa)

13 Alpha and Beta radiation effects on Re2MnCoO6 (Re = La, Sm, Nd)

The rise in global demand for nuclear technology has resulted in an increase in radioactive waste and radioactive material. Some of these radioactive materials and nuclear waste undergo radioactive decay, emitting alpha and beta particles. Beta particles are energetic electrons with a single negative charge, while alpha particles are equivalent to a helium atom with a charge of +2. Both alpha and beta particles can cause significant damage along their path of travel. Therefore, there is a need for materials used for radiation shielding. This study was therefore aimed at simulating the effects of alpha and beta radiation on Re2MnCoO6 (Re = La, Sm, Nd) prepared by solid-state method.
The stoichiometric ratios of the starting materials were measured and ground into a fine powder then calcined at 900 oC for 12 hours before being annealed at 1200 oC for a further 48 hours. Finely ground samples were characterised by powder X-ray diffraction (XRD) to ascertain that the right structures were crystallized. A continuous scanning using Cu-Kα radiation (40 kV, 30 mA) was done, measuring between 10° and 90° with a step of 0.02° and speed of 0.145 s/step. The samples were indexed to the monoclinic phase of Re2MnCoO6 that belongs to a space group P21/n, number 14.
The continuous slowing-down approximation (CSDA) range of beta particles in the samples and the stopping power of the samples have been calculated using ESTAR. At 0.5 MeV, the beta particles have an CSDA range of 0.018 g/cm2 for Sm2MnCoO6, 0.2699 g/cm2 for Nd2MnCoO6 and 1.370 g/cm2 for La2MnCoO6. The mass stopping power of all the three samples decreases with energy up to about 1 MeV and then starts to increase again.
The ranges, energy deposition and displacement damages caused by alpha particles have been estimated using the ion transport Monte Carlo simulations using the Stopping and Range of Ions in Matter (SRIM) code with the Full Damage Cascades mode. A 4 MeV alpha particle has a range of about 23.53 µm in Sm2MnCoO6, 23.08 µm in Nd2MnCoO6 and 22.00 µm in La2MnCoO6. The mass stopping power for all the three samples ranged between 0.320 MeV.cm2/g and 0.414 MeV.cm2/g for a 0.1 MeV alpha particle.
The results show that double perovskites can be used as matrices for radioactive waste immobilization.

Speaker: Tinashe Dhliwayo (University of Johannesburg)

14 Radiation contamination in gold mine tailings soil samples using HPGe spectrometry

An assessment of the radiation concentration in abandoned mines located near settlements in the west of Johannesburg was carried out, and the corresponding radiological indices were determined. In this study, a gamma spectrometer was used to measure the activity concentrations of radionuclides in the soil samples. The activity concentrations for ²²⁶Ra, ²³²Th, and ⁴⁰K were 338.44±3.48, 10.06±0.68, and 126.15±10.90 Bq/kg, respectively. The results revealed that the average activity concentrations at some locations exceeded the world average for some of these nuclides.

Speaker: M.J. Mvelase

15 The low-lying electric dipole strength in nuclei: the role of deformation

The electric dipole response in nuclei is characterised at high energies by the isovector Giant Dipole Resonance (IVGDR) and, for neutron-rich nuclei, by the Pygmy Dipole Resonance (PDR) around the neutron separation energy. Even though these two excitation modes have been extensively studied, some of their characteristics are still not understood. This talk will concentrate on the discussion of the role of deformation in the excitation of the PDR. Two independent experiments were performed to study the electric dipole response of the quadrupole-deformed 154Sm nucleus. The inelastic scattering of 120-MeV alpha particles was studied at iThemba LABS while 295-MeV protons were used at RCNP. The first comparison of the isoscalar and isovector responses of the a the deformed nucleus will be presented.

Speaker: Luna Pellegri (University of the Witwatersrand and iThemba LABS)

16 Nuclear structure investigations via the (p,d) neutron removal reaction

Nuclear structure studies are essential for unraveling the complex interactions between the nucleus and nuclear forces, as well as understanding how shell effects emerge throughout the nuclear chart. High-precision measurements of nuclear properties—including energy levels, spins, parities, and spectroscopic factors—offer valuable insights into the nucleus's internal structure and play a key role in testing and improving nuclear models. In this presentation a detailed investigation of the 36S(p,d)35S neutron-removal reaction using a 66 MeV proton beam will be presented, probing nuclear structure and the Fermi surface of sd nuclei. A strong j-dependence for l = 2 states will be revealed, providing refined insights into spin-orbit splitting and shell rigidity. The findings, including spectroscopic factors of states which includes isobaric analog state contributions, advance our understanding and offer benchmark data for theoretical models.

Speaker: Retief Neveling (iThemba LABS)

Nuclear, Particle and Radiation Physics-2

17 Highlights of ALICE results from heavy-flavour measurements at LHC energies

Edith Zinhle Buthelezi for the ALICE Collaboration

Heavy quarks or heavy flavours (charm and beauty) are produced mainly in initial hard-scattering processes of hadron-hadron collisions. Due to their large masses, their production cross sections are predicted via perturbative quantum chromodynamics (pQCD) models. They offer a unique perspective to study quark fragmentation and hadronisation. In ALICE, heavy flavours are measured via the hadronic and leptonic decay channels in small-system collisions, e.g. proton-proton (pp) and proton-lead (p-Pb), as well as in heavy-ion (Pb-Pb) collisions at ultrarelativistic energies provided by the CERN Large Hadron Collider (LHC).

This presentation will focus on a selection of heavy-flavour results published by the ALICE collaboration.

Speaker: Edith Zinhle Buthelezi (NRF-iThemba LABS)

18 Parton Production Spectra and Energy Loss in High-Energy $O$$O$ Collisions

We compute the production spectra for high-momentum light quarks and gluons in high-energy hadron collisions at a variety of center-of-mass energies, some of which are previously unstudied. These spectra provide the foundation for making quantitative predictions of parton energy loss in high-multiplicity hadronic collisions at RHIC and the LHC. Thus these spectra are necessary in order to use high-momentum partonic probes as a femtoscope to quantitatively characterize the properties of the novel state of matter produced in high-multiplicity hadronic collisions, the quark-gluon plasma. We demonstrate the success of our methodology and implementation by reproducing previously known theoretical results; we then successfully compare our calculations with recent experimental data; finally, we make quantitative first predictions for the production spectra necessary for the future $O+O$ collisions at LHC in the second half of 2025.

Speaker: Mohammad Alam (University of Cape Town)

19 Real-Time Anomaly Detection in High Energy Physics

While searches for physics beyond the Standard Model (BSM) have yet to yield conclusive discoveries, they continue to motivate the development of more flexible, data-driven strategies. At the ATLAS experiment at the Large Hadron Collider (LHC), trigger systems are used to rapidly select potentially interesting proton–proton collisions for further analysis. Traditional triggers rely on pre-defined criteria, such as high-momentum particles, which may miss more subtle or unconventional signs of new physics. To overcome this limitation, machine learning algorithms are being developed to identify anomalous events in real time based on their overall detector signature, rather than specific features. Using unsupervised learning techniques, these algorithms learn to characterise typical collision patterns directly from the data, without input from Standard Model or BSM theory. Events that diverge significantly from these patterns are flagged as anomalous for further study. Such events are stored for detailed offline analysis. This approach enables a broad and largely model-independent search for unexpected phenomena in the vast datasets of Run-3 and beyond, potentially revealing signals that targeted BSM searches might overlook.

Speaker: Ryan Atkin (University of Cape Town)

Photonics: Photonic Quantum Technologies & Quantum Optics

Convener: Angela Dudley

20 Comparative Theoretical Analysis of Entangled Quantum States for Enhanced Sensing Application

Quantum sensing leverages the distinct characteristics of quantum states to surpass classical measurement precision limits. We propose a theoretical study which provides a comparative analysis of various entangled quantum states, specifically NOON states, twisted NOON states, entangled coherent states, and BAT states, for advanced sensing applications. We evaluate each state's phase estimation precision, and robustness to noise and decoherence. NOON states offer remarkable phase sensitivity but face significant challenges with photon loss and decoherence. Twisted NOON states introduce angular momentum modes, potentially enhancing sensitivity and noise resistance in structured sensing scenarios. Entangled coherent states provide flexibility with adjustable amplitudes and resilience to photon loss, while BAT states balance enhanced sensitivity with improved noise tolerance through hybrid quantum states. The comparative assessment includes theoretical noise modeling and considers losses to the environment.

Speaker: Kelvin Mpofu (CSIR)

21 Rate equations for the control of Yb-171 ions

Trapped ions are promising candidates to use as qubits in quantum computers, offering long coherence times, scalability, and precise control of the states of each ion individually by means of lasers. The long-term goal of this quantum control project is to achieve unsharp measurements with two isotopes of ytterbium, Yb-171 and Yb-174, in a linear Paul trap. To predict and interpret experimental results for one of the species, Yb-171, we numerically model the atom-radiation interactions using rate equations. Rate equations are a set of coupled, first-order differential equations describing the time-dependent evolution of the ion’s hyperfine state populations due to transitions between levels.
We semi-classically model the interaction between the ion valence structure and lasers, which includes electric dipole and electric quadrupole transitions. Using the model, we analyse hyperfine state population dynamics to gain insights on how to increase the efficiency of and estimate timescales for various quantum control processes used experimentally. These processes include doppler cooling, state preparation , electron shelving and state detection. Ions are doppler cooled to reduce their kinetic energy so that they remain trapped, enabling precise control and manipulation. Doppler cooling is estimated in the simulation as an accumulation of spontaneous emission due to driving a transition. State preparation initialises the ion into the qubit ground state. We model electron shelving by populating and depopulating a long-lived metastable state by pumping an electric quadrupole transition. State detection is performed by pumping a closed loop transition that produces measurable fluorescence. To recover efficiency of these processes, several additional lasers are used to depopulate dark states.
Understanding how these processes influence the ion’s state is crucial for optimizing them, ultimately improving future experimental control and efficiency in the laboratory.

Speaker: Abigail Iyer (University of Stellenbosch)

22 Decay of stationary entanglement mediated by one-dimensional plasmonic nanoarrays

Metal nanoparticles have been shown to be good mediators for entanglement generation in plasmonically-coupled quantum dot qubits. These mediators enable entanglement to be sustained over long qubit-qubit distances. We investigate the impact of the number of mediating particles on the generation of bipartite entanglement by considering both parallel and perpendicular nanoarrays with respect to the interaction axis of the qubits and the polarization of the driving field. The plasmonically-coupled qubits were investigated within the framework of cavity quantum electrodynamics. The metal nanoparticles were arranged in a collinear fashion using a periodic spacing and a particle size that allow their interactions to be treated within the dipole approximation. We employ an effective approach that enables the investigation of plasmon-mediated stationary entanglement in the coupled qubits. We show that our approach agrees with simulations. The degree of stationary entanglement was found to decay exponentially with increase in the number of mediating particles in the nanoarray.

Speaker: Dr Luke Ugwuoke (Stellenbosch University)

Physics for Development, Education and Outreach

23 An Introduction to Quantum Computing - Teaching the Basics

Quantum computing, a field that started gaining increased traction around
2016, uses quantum mechanics principles from around 1900 to compute with
quantum phenomena rather than the random simulations of classical computers. This
interactive presentation introduces quantum computing to people without a
background in computing or quantum mechanics. It compares classical logic
gates and circuits to quantum ones to build understanding. The session covers
set theory and probability as steps toward quantum states and Bloch spheres.
It ends with quantum circuits and simple algorithms, using hands-on examples
to demystify quantum computing, allowing attendees to grasp its core
principles and potential.

Speakers: Prof. Ken Nixon (Wits University), Dr Taariq Surtee (Wits University)

24 INVESTIGATING THE EFFECT OF MATERIAL PROPERTIES ON THERMAL CONDUCTIVITY: AN INQUIRY-BASED APPROACH

This study investigates the effect of material properties, specifically wood, plastic, and steel, on thermal conductivity through an inquiry-based approach. Thermal conductivity is a key factor influencing heat transfer in various applications, from construction to manufacturing. The research explores how the intrinsic properties of these materials, including density, structure, and composition, affect their ability to conduct heat. By focusing on common materials like wood, plastic, and steel, the study provides a comparative analysis of their thermal performance. Experimental and theoretical methods were employed to examine the heat transfer characteristics of each material under different conditions. The results reveal that steel, with its high density and metal structure, exhibits the highest thermal conductivity, while wood, being a natural insulator with a porous structure, shows the lowest thermal conductivity. Plastics exhibit intermediate thermal conductivity values depending on their type and molecular structure. The findings emphasize the significant role of material composition and structure in determining heat transfer efficiency, offering valuable insights for selecting materials in energy-efficient designs. This inquiry-based approach deepens the understanding of thermal conductivity in diverse materials and encourages further exploration into how these properties can be optimized for various industrial applications.

Speaker: Dr Halalisani Mngomezulu (University of Johannesburg)

25 Transforming Physical Sciences Teaching through Targeted Professional Development

Physical Sciences teachers in under-resourced South African schools often face systemic challenges, including limited access to continuous professional development, inadequate teaching resources, and insufficient support for both content and pedagogy. These challenges frequently result in teacher-centred practices that hinder learners’ development of conceptual understanding and procedural knowledge. This paper presents findings from a professional development initiative led by the Department of Physics and Astronomy at the University of the Western Cape, aimed at addressing these issues in surrounding schools. The programme included interactive workshops, collaborative lesson planning, and classroom-based support, with a particular focus on promoting learner-centred approaches such as Modeling Instruction. Data were collected through teacher surveys, pre- and post-tests, and reflective activities to assess changes in content knowledge and pedagogical practice. The findings reveal increased teacher confidence and notable improvements in both content knowledge and the adoption of learner-centred teaching strategies. This study contributes to the ongoing discourse on designing contextually relevant and sustainable professional development models for science educators in resource-constrained environments.

Speaker: Dr Mark Herbert (University of the Western Cape)

Physics for Development, Education and Outreach

Convener: Paul Molefe

Physics of Condensed Matter and Materials

Physics of Condensed Matter and Materials 2

Theoretical and Computational Physics: Session 1

Convener: William Horowitz (University of Cape Town)

26 Shock Wave Propagation in Core-Collapse Supernovae: A One-Dimensional Study with Magnetic Fields

Core-collapse supernovae involve extreme conditions where gravity, nuclear physics, and shock hydrodynamics interact to drive the explosive disruption of a massive star. In this study, we investigate shock wave propagation using a one-dimensional piston-driven model as a proxy for the bounce shock that forms during core collapse. A polytropic equation of state is employed to represent thermodynamic behavior, and magnetic fields are included to examine their role in modifying shock dynamics and matter compression. Numerical simulations, complemented by analytical estimates, reveal how magnetic effects alter post-shock structures and energy transport.

This model offers a simplified but physically insightful framework for studying magnetically influenced shocks in astrophysical environments. It also provides conceptual parallels with shock propagation in high-energy nuclear collisions, where similar compressional dynamics are observed. By combining tractable fluid models with magnetic fields, the study contributes to the theoretical and computational understanding of both stellar collapse and strongly interacting matter under extreme conditions.

Speaker: Prof. Azwinndini Muronga (Nelson Mandela University)

27 ID 417

Speaker: Magdeline Seabi (Nelson Mandela University)

28 Energy Loss as a Probe of Quark-Gluon Plasma Formation Across Collision System Size

The quark-gluon plasma (QGP) is formed when protons and neutrons melt at temperatures over 100,000 times hotter than the Sun’s core. These conditions are achieved in high-energy heavy-ion collisions, such as those involving lead or gold nuclei at the Large Hadron Collider (LHC) and the Relativistic Heavy Ion Collider (RHIC). More recently, signs suggest that small droplets of QGP may also form in rare, high-activity proton-proton and proton-lead collisions. One way to study the QGP is by measuring how much energy high-momentum particles—produced early in the collision—lose to the medium. If QGP forms in small systems, a suppression of high-momentum particles should also be observed; however, there is currently no conclusive evidence of energy loss in small systems. In this work, we use a statistically driven analysis of $R_{AA}$ data from heavy-ion collisions to constrain the effective strong coupling in our energy loss model, which includes corrections for small system sizes. We also quantitatively estimate various theoretical uncertainties to evaluate the robustness of our conclusions. With the model constrained using only large-system data, we make predictions for small systems with no further tuning and compare them to experimental results at RHIC and LHC. We find that high-momentum particle suppression in central small systems is comparable to that in peripheral heavy-ion collisions, consistent with RHIC data and with LHC heavy-ion results—but in stark disagreement with LHC small-system measurements. We show that this equal suppression in peripheral large systems and central small systems holds across a variety of simple energy loss models. We argue that the LHC small-system discrepancy is likely due to event selection biases in the measurements, to which RHIC data are less sensitive.

Speaker: Coleridge Faraday (University of Cape Town)

10:20 AM Morning Tea

Applied Physics

Convener: Adiel Holtzhausen (Akademia)

29 Physical Principles to Translate from Phase Contrast Imaging to Absorption Contrast Imaging

Artificial Intelligence (AI) classification as a methodology and approach to identify Tuberculosis (TB) in patients has become a topic of increasing interest in the past few decades. This is in large part due to the increasing demand for faster methods of detecting TB to reduce spread. However, such methodologies require large datasets so that algorithms can learn the manifestations of TB in the lung. Some of these datasets are private due to patient confidentiality, and the publicly available ones are limited in number. The AI industry has exhausted publicly available chest X-ray (CXR) scans and now look for alternate methods to further develop research in the field. The study focuses on developing methods to translate 3D information on effective electron density from Hierarchical Phase Contrast tomography (HiP-CT) of a human lung to 3D segmented images based on differentiated effective atomic number and mass density. The purpose of this methodology is to create a digital phantom as a synthetic model of a human lung where pathologies of the various stages of TB can be inserted. Monte Carlo modeling of X-ray radiography can then be performed on sets of such digital phantoms to produce a library of 2D conventional X-ray radiographs labeled with details of the occurrence of TB pathologies. This synthetic data set can be used to train an AI classifier.

The study will leverage HiP-CT scans produced by the European Synchrotron Research Facility (ESRF) beamline BM18. These are high-resolution 3D scans (~20$\mu$m) of complete human organs. To create a synthetic dataset, the Geant4 toolkit will be used to simulate the properties and physiological conditions of a lung. This information is gathered from the HiP-CT images; to understand the material properties of the HiP-CT images, the phase shift ($\delta$) and the effective mass densities ($\rho_{eff}$) of the organic materials within the lung must be known. Thus, this research builds on the derivation of equations and the calculation of these parameters as inputs for simulation.

Speaker: Mr Preveshin Maduray (University of Johannesburg)

30 Development and Qualification of a Fiber Optic Sensor Package for ITk Environmental Monitoring

The High-Luminosity Large Hadron Collider  requires precise environmental monitoring in the ATLAS Inner Tracker  to prevent water condensation that could damage detector electronics. This study focuses on the development and the performance of Fibre Optic Sensor  packages. Each package is made up of a Long Period Grating sensor  and two Fibre Bragg Grating sensors for accurate temperature, dose and relative humidity measurements in a harsh radiation environment [1]. Extraction of the relative humidity (and Dew point) involves the decoupling of the effects of the measured temperature and radiation dose which requires compensation  to be accurate. The temperature and relative humidity measurements may depend on location in the 2D (temperature, relative humidity) plane, as indicated by some measurements. This could be an effect  of the packaging or a systematic physics effect of the FOS sensors.  Calibration studies were performed to  assess any possible dependency of temperature calibration on relative humidity in order to determine whether it arises from real sensor sensitivity or external factors such as packaging constraints. Calibration protocols were extended, and compensation algorithms refined to improve measurement accuracy. We present the outcome of the made Fibre Optic Sensor package and compensation methodology to ensure stable ATLAS Inner Tracker conditions for the High-Luminosity Large Hadron Collider era.

[1] L. Scherino et al., "Fiber optic sensors in the ATLAS Inner Detector," Nucl. Instrum. Methods Phys. Res., Sect. A, vol. 1029, p. 166470, 2022, doi: 10.1016/j.nima.2022.166470.

Speaker: Doomnull Unwuchola (University of the Western Cape)

31 Combining spheres and spirals of light for noise free communication through optical fibre

Topology has played a significant role many areas in Physics, ranging from cosmology and condensed matter to high-energy physics and waves. In electromagnetism, one can create an optical Skyrmion through correlations between position and polarization which map from real space to the Poincaré sphere. These topological states of light can be realised in classical laser beams and biphoton entangled states, demonstrating remarkable resilience in both regimes to a wide range of perturbations and noise. This makes them a viable candidate for information encoding and transport, promising inherent robustness and a higher dimensional encoding alphabet. However, optical Skyrmions are not resilient to modal noise, currently hindering their implementation in multimode optical fibres which are necessary for the long range and high-speed transmission of information. In this work we leverage the recently discovered phenomenon of topological confinement in optical fibres for light with spiral wavefronts to greatly diminish the effects of modal noise. Our findings demonstrate the potential for Skyrmions to be transported over large, previously unreachable distances by leveraging two topological phenomena. This opens the doorway for the use of optical Skyrmions in communication networks as a means for encoding and transporting information in a manner that is robust to virtually all forms of noise.

Speaker: Cade Peters (Univeristy of the Witwatersrand)

32 Energy Balance Closure Analysis Based on Eddy Covariance Flux Tower Observations

Energy balance closure is a fundamental principle in micrometeorology, ensuring that all energy fluxes within an ecosystem are properly accounted for. The eddy covariance (EC) method, widely used for measuring land – atmosphere exchanges of energy and mass, often exhibits energy closure discrepancies, particularly across different timescales. This study investigates ecological year energy closure using flux tower data collected over multiple years at Skukuza, Kruger National Park. Energy closure was assessed using the fundamental balance equation R_n-G=H+LE, where net radiation (R_n ), soil heat flux ( G), sensible heat flux (H), and latent heat flux (LE) were analyzed across different timescales. Radiation shields and soil heat flux sensors were employed to capture variations in energy fluxes. Statistical analysis of multiple ecological years revealed that energy closure varies significantly with seasons, with wetter years exhibiting lower energy imbalances compared to drier years.

The findings indicate that energy closure improves with increased turbulence (frictional velocity) but remains incomplete due to measurement uncertainties, sensor sampling scales, and ecosystem heterogeneities. Results highlight a persistent energy closure gap, with an average closure of approximately 80%, consistent with other EC studies globally. The study underscores the challenges in achieving full energy balance closure and emphasizes the need for improved sensor calibration, turbulence parameterization, and data correction techniques. These insights are crucial for refining EC methodologies and enhancing the accuracy of land-atmosphere energy exchange assessment in semi-arid ecosystems.

Speaker: Mr Lufuno Takalani (University of Venda)

33 Towards Single-Electron Transport in Engineered Low-Dimensional Semiconductor Devices

Quantum electron pumps (QEPs) have become more popular as sources of precision current as the ampere is being redefined in terms of basic constants. As possible platforms for QEPs, this study investigates the fabrication and integration of engineered low-dimensional semiconductor materials, specifically silicon nanowires and C₆₀ fullerene nanorods. Through a combination of nanofabrication techniques such as chemical vapour deposition (CVD) growth and electron beam lithography (EBL), this work focuses on synthesizing, characterizing, and preparing these materials for quantum transport applications. Although full low-temperature testing is ongoing, the study establishes a robust foundation for future quantised current measurements by addressing key fabrication challenges and integration strategies. The project ultimately contributes to the broader effort of advancing metrological standards using novel nanostructures.

Speaker: Mr Aluwani Guga (University of Cape Town/iThemba Labs)

Astrophysics & Space Science: Cosmology

34 Structure growth in the thawing dark energy models

In this work, we study the dynamics of the universe using Thawing Dark Energy (TDE) model with a minimally coupled scalar field that evolves away from the dominance of potential energy. As the equation of state parameter 𝑤(𝑎) evolves, this offers a dynamic framework where the impact of dark energy may change over time. The structure formation of the universe will be highlighted in TDE using the redshift space distortion data together with cosmic chronometers (CC) baryon acoustic oscillation (BAO) data taken from the Dark Energy Spectroscopy Instrument (DESI) and the SNIa distance moduli measurements from the Pantheon + SH0ES survey, which consist of 1701 light curves of 1550 distinct supernovae. After introducing the background cosmological solutions and numerical findings, the linear cosmological perturbation equations will be derived in the 1+3 covariant formalism to analyse the numerical density fluctuations. The detailed statistical analysis will be performed after we calculate the best fit cosmological parameters through MCMC simulations.

Speaker: Shambel Akalu (North-West University)

35 Constraints on Cosmological Parameters Using a Large Sample of Gamma-Ray Bursts with their redshift derived by Machine Learning

Various empirical correlations between observable and derived parameters have been proposed to use Gamma-Ray Bursts (GRBs) as standard candles similar to Type Ia supernovae (SNe Ia) for measuring cosmological distances. The Yonetoku relation, which connects the intrinsic peak energy to the isotropic peak luminosity, stands out as a promising tool. In this work, we present results from machine learning models applied to GRBs, from the Fermi-GBM and Kouns-Wind catalogs, to estimate their redshifts. These models, based on peak-flux intervals and parameter fittings from both datasets, allow us to explore the Yonetoku correlation using GRBs with pseudo-redshifts. We focus on estimating the distance modulus and constraining cosmological parameters using this relation. Our analysis includes 1576 GRBs with pseudo-redshifts (publicly available via Zenodo) and 116 GRBs with spectroscopic confirmed redshifts from the Fermi-GBM catalog. Additionally, we incorporate recent SNe Ia samples from SNe U2.1 and the Dark Energy Survey (DES-SNe). Unlike previous studies, we perform a simultaneous calibration of the Yonetoku relation and cosmological parameters using a Markov Chain Monte Carlo (MCMC) method, applied across both the full redshift range and within specific redshift bins, assuming a flat universe within the Lambda Cold Dark Matter (ΛCDM) model. This work aims to assess the potential of leveraging a large sample of GRBs with pseudo-redshifts from the Fermi-GBM and Kouns-Wind catalogs to provide meaningful constraints on cosmological models.

Speaker: Ms Tamador Khalil Mansoor Aldowma (University of Johannesburg)

36 Cosmological model in f(R,G,T) gravity

We study an FLRW cosmological model in $f(R,\mathcal{G}, T)$ gravity by assuming a specific form of the deceleration parameter. A Markov Chain Monte Carlo (MCMC) analysis is performed using the Cosmic Chronometer and Pantheon datasets to determine the parameters of the model. A viable model is obtained which exhibits a transition from deceleration to acceleration and which satisfies observational constraints. The various cosmographic parameters such as the deceleration, jerk and statefinder parameters are analysed and illustrated. A comparison is made with the standard $\Lambda$CDM model. Finally the energy conditions and equation of state are discussed. By studying this model, we get further knowledge and understanding of the dynamics and evolution of the cosmos.

Speaker: Aroonkumar Beesham (University of Zululand)

37 Constraining the Teleparallel Universe

The latest DESI results, suggesting a dynamical dark energy equation of state, have reinvigorated interest in modified teleparallel theories, such as $f(T)$ gravity, as viable alternatives to the standard cosmological model. In this talk, I present a systematic investigation of several popular and novel $f(T)$ models, examining their viability in light of current observational data. By applying recent cosmological datasets, including Type Ia Supernovae, Plank 2018, BAO, and Hubble parameter measurements, we derive constraints on key model parameters and explore the sensitivity of each model to different datasets using Monte-Carlo-Markov-Chains. The analysis not only highlights which forms of $f(T)$ are most favored by data but also identifies unique signatures that could distinguish torsion-based gravity from curvature-based frameworks. This work contributes toward the broader goal of building a consistent, observationally viable theory of gravity beyond the standard paradigm.

Speaker: Robert Rugg (North-West University)

38 Bispectrum correlations of HI intensity mapping and large-scale structure surveys

Neutral hydrogen (HI) intensity mapping (IM) experiments
probe the large-scale structure of the universe through the integrated
redshifted 21-cm line emission from unresolved sources of neutral
hydrogen. Optical surveys also probe the large-scale structure of the
universe with much higher precision and depth by mapping the galaxy
distribution. In this article, we study the cross-correlations of the
HI IM field from HIRAX (Hydrogen Intensity and Real-time Analysis
eXperiment) with the galaxy density and cosmic shear fields from the
Rubin observatory large-scale structure survey, laying down the tools
to do parameter forecasts and study constraints on the neutral
hydrogen fraction, galaxy bias, and cosmological parameters.
Astrophysical foregrounds limit the long-wavelength line-of-sight HI
modes, reducing the constraining power of these cross-correlations. We
introduce bispectrum estimators, specifically HI-HI-galaxy density and
HI-HI-shear cross bispectra estimators, to recover modes lost in the
foreground subtraction process and improve the parameter constraints.

Speaker: Moumita Aich (University of Witwatersrand)

Nuclear, Particle and Radiation Physics-1

Nuclear, Particle and Radiation Physics-2

39 Analysis of Long-Term Stability Uncertainty in Luminosity Measurements Using the Tile Calorimeter of the ATLAS Detector for Run 3 Proton-Proton Collisions at $\sqrt{s} = 13.6$ TeV in 2023

Precision luminosity measurements are crucial for determining the fundamental properties of physics processes at the Large Hadron Collider (LHC). In the ATLAS experiment, luminosity uncertainties often represent one of the leading sources of systematic uncertainty in cross-section measurements, directly impacting sensitivity to new physics searches and background estimations.

Since the calibration of the primary luminometer of ATLAS, LUCID, is performed only once per data-taking year, studying the long-term stability of LUCID luminosity measurements is crucial, as it significantly contributes to the total uncertainty in the ATLAS luminosity measurement. In this study, the Tile Calorimeter is used to evaluate and monitor the long-term stability of the luminosity measurements. Results are presented for the ATLAS detector during proton-proton ($pp$) collisions at $\sqrt{s} = 13.6$ TeV in 2023. A long-term stability uncertainty of $\delta L/L = 0.1\%$ is obtained for the 27.58 fb$^{-1}$ of data delivered to ATLAS.

Speaker: Phuti Rapheeha (University of the Witwatersrand)

40 South Africa’s Contribution to the Phase-II Upgrade of the ATLAS Hadronic Tile-Calorimeter Low-Voltage Power Supply

The High-Luminosity Large Hadron Collider (HL-LHC) is scheduled to begin operation in 2030. While the increased luminosity presents exciting opportunities for new scientific discoveries, it also introduces significant technical challenges for the ATLAS detector systems. To meet these demands, the ATLAS Hadronic Tile Calorimeter (TileCal) will undergo a comprehensive Phase-II upgrade during the third long shutdown (LS3) of the LHC.

A key component of this upgrade is the replacement of the on-detector electronics, which are powered by 256 Low-Voltage Power Supplies (LVPS). Each LVPS unit contains eight transformer-coupled buck converters, known as "Bricks," which step down the power delivered from off-detector bulk supplies to the required levels for the front-end electronics.

The South African cluster, led by the University of the Witwatersrand, is responsible for the research and development, production, quality assurance testing, and integration of half of the required Bricks for the Phase-II upgrade.

This presentation will provide an overview of South Africa’s contributions to the LVPS Brick development for the TileCal upgrade. It will highlight key project milestones such as the recent pre-production, an essential step in preparing for full-scale production, and will conclude with a forward-looking perspective on the upcoming main production of the final Brick units.

Speaker: Ryan Mckenzie (University of the Witwatersrand)

41 Early Failures Detection with Machine Learning for ATLAS TileCal LVPS: The Impact of Burn-in Assessed with Test Bench Datasets

The Large Hadron Collider (LHC) is undergoing a high-luminosity upgrade to increase its luminosity, affecting the ATLAS detector and, consequently, its hadronic Tile-Calorimeter (TileCal). As part of the ATLAS Phase-II Upgrade to adapt to the new high-luminosity environment, the TileCal is upgrading its low-voltage power supplies (LVPS) that power its on-detector front-end (FE) electronics. Over 1000 boards (Transformer-coupled buck converters) housed within the LVPS will be manufactured in South Africa. Quality control is crucial due to the limited access to the boards once installed in the inner-barrel of the TileCal. A board failure would result in offline FE electronics, degrading detector performance. This study aims to improve the current quality control procedure by integrating machine learning techniques as anomaly detection models. The analysis is based on production data collected from 1032 LVPS boards, functional parameters are measured using two test bench stations to ensure that the boards operate within the specified design limits. By comparing the measurements obtained from the two test bench stations, both with and without the inclusion of a burn-in step, valuable insights can be gained into the impact of burn-in on the quality control process. This comparative analysis aims to identify the critical functional parameters that contribute to high accuracy in detecting anomalies and identify potential defects in the LVPS boards and ultimately minimizing the risk of deploying faulty boards in the TileCal at CERN.

Speaker: Dr Chuene Mosomane (iThemba Labs)

42 Investigation of Radiation-Resistant Components for the TileCal-ATLAS Detector

The performance and longevity of photomultiplier tubes in high-radiation environments, specifically the Tile Calorimeter, are crucial to the ATLAS detector’s efficiency. This research is part of an ongoing investigation into the electron emission yield and electronic properties of various materials to be used in the dynode chain, the main component of the photomultiplier tubes. This study aims to inform material selection for future radiation-hard PMT designs in the upcoming high-luminosity upgrade to the Large Hadron Collider. The materials of interest include aluminium oxide, gallium arsenide, thallium doped caesium iodide, and magnesium oxide. The changes in the electronic properties and electron emission yield before and after irradiation are studied. Results for the electronic properties were obtained using an electrical system optimised to measure high resistance. In addition to this, data pertaining to the electron emission yield has also been acquired using the Proton Microprobe at iThemba LABS’ TANDEM accelerator.

Speakers: Gaurav Lall (University of the Witwatersrand), Dr Othmane Mouane (University of the Witwatersrand)

43 Particle Flow Algorithm (PFA) development for forward jet reconstruction with the ATLAS ITk detector setup at the HL-LHC

The ATLAS experiment at the High-Luminosity Large Hadron Collider (HL-LHC) will require advanced reconstruction techniques, particularly in the forward region, to cope with increased pile-up. This work presents a Particle Flow Algorithm (PFA) development for the ITk detector, focusing on tower clusters rather than traditional topological clusters in the η = ⟨0 − 1.5⟩ region. The forward region indicates η = ⟨2 − 4⟩. The strategy integrates tracker momentum measurements with calorimeter energy deposits through cell-based subtraction, prioritising energy density layers to resolve overlaps between tracking and calorimetric data. By employing tower clusters, which aggregate calorimeter cells into fixed η × ϕ grids, we aim to improve computational efficiency while maintaining spatial granularity critical for forward jet reconstruction. The framework processes Event Summary Data (ESD), containing raw detector-level information (tracker hits, calorimeter clusters), and it is processed into Analysis Object Data (AOD), a condensed format storing high-level physics objects (jets, leptons) optimised for analysis. The algorithm refines energy subtraction and calibration by implementing Gaussian fitting of ⟨E/p⟩ distributions across calorimeter layers, mitigating pile-up effects in the forward region. This approach addresses the high-pileup HL-LHC environment, balancing precision in jet energy resolution with computational scalability for the ITk detector’s upgraded granularity.

Speaker: Thabo James Lepota (School of Physics and Institute for Collider Particle Physics, University of the Witwatersrand)

Photonics: Photonic Quantum Technologies & Quantum Optics

Convener: Isaac Nape (University of the Witwatersrand)

44 Noisy quantum channels fail to rip the fabric of entanglement

Non-local entangled states are an important resource for future quantum technologies, but their practical use is hindered by the effects of noisy quantum channels. However, recently discovered quantum Skyrmions, topologically structured entangled states, offer a promising solution. In this work, we develop a theoretical framework to study the evolution of entangled states and their topology in general quantum channels. Using photons entangled in orbital angular momentum and polarization as an example, we demonstrate that noise can be interpreted as a smooth geometric transformation of the mapping between the two-photon state spaces. From this, we predict complete resilience of the topology of the states against both depolarizing and non-depolarizing noise. Additionally, we identify specific sources of local noise that may destabilize the topology and discuss mitigation strategies. Our results have direct implications for quantum information distribution in noisy environments, including quantum computing and quantum networks.

Speaker: PEDRO DINIS ORNELAS (University of the Witwatersrand)

45 Tunable hybrid and non-local entanglement in photon pairs

Tailoring light’s degrees of freedom and coupling them to enable complex transformations has become topical, with applications spanning high-dimensional information processing to advanced imaging systems at both classical and quantum levels. In this work, we introduce a voltage-controlled, multiwavelength spin–orbit coupling approach to engineer the entanglement properties of photon pairs generated via non-degenerate spontaneous parametric down-conversion. By adjusting the operational voltage, the device modulates its transformation rules, enabling a controlled transition from a configuration with non-local correlations across photons to one featuring local hybrid entanglement within a single photon. This versatile tool for structuring photonic states paves the way for interesting applications in quantum information processing.

Speaker: mwezi koni (university of the witwatersrand)

46 Investigating Second-Order Correlation of a Single-Photon Source NV Centre under CW Excitation

In this work, we investigate the quantum light emission properties of single nitrogen-vacancy (NV) centres in diamond under continuous-wave (CW) excitation at a wavelength 532 nm while the emitted photons have a wavelength of 637 nm. Using Hanbury Brown and Twiss (HBT) interferometry, we measure the second-order correlation function (g²(τ)) to characterize the photon statistics of the single-photon source confirming the emission of one photon at a time, i.e. antibunching. NV centres are known for their exceptional stability at room temperature and their ability to emit single photons. These capabilities are driven by a high-power green laser, ensuring efficient excitation while minimizing multi-photon emission. Our findings reveal strong antibunching at zero-time delay in the HBT interferometer, indicative of single-photon emission, with detailed insights into the temporal coherence of the emitted photons. The study highlights the potential of NV centres as a robust source of quantum light for applications in quantum communication, quantum cryptography, and quantum information processing. Additionally, we discuss the effects of CW excitation on the photon emission dynamics and explore strategies to enhance the purity of emitted single photons in future applications.

Speaker: Shaman Bhattacharyya

47 Revealing the quantum nature of a continuous laser carrying orbital angular momentum

Revealing the quantum nature of a source that generally is considered classic radiation is significant. In quantum optics and generally in optics we have the scalability problem as the experiment extends. Hence, finding sources that can overcome this challenge is essential. Radiation from a continuous wave (CW) source is described by the dynamics of quasi-classical (coherent) states. Such a source, though abundant with photon rate but fail to represent a single-photon source. Theoretically, the quantum aspect of such states can be observed in the weak limit hinting to the high single-photon rate. Yet, since these states are superposition of different particle-states of radiation, we need post-selection to achieve this result and within the weak limit. However, this high rate has never been observed. In this work, we experimentally demonstrate that the weak limit of quasi-classical states supplemented by orbital angular momentum (OAM) can deliver a high photon rate producing a quantum signature. Through our experiment, we realize two-photon bunching with the projection of OAM from a continuous wave source. We observe that this approach can produce the result from a single photon source with high accuracy after the post selection. In addition, this can be considered as confirmation that OAM is an intrinsic property of light at the quantum level. In fact, since there is no interaction with matter, the post-selected photon rate from this approach can be considered as an upper bound for the single-photon generation based on the input power. This work is a step forward toward a more diverse and practical use of quasi-classical states in the domain of quantum optics and quantum information.

Speaker: Moslem Mahdavifar (University of the Witwatersrand)

48 Revealing the unseen with tailored quantum light

Quantum ghost imaging offers an interesting approach to imaging, harnessing entangled photon pairs to capture images using photons that never directly interact with the object. Traditionally, this technique relies on costly single-photon cameras or pixelated projective masks, where image resolution is fundamentally limited by the pixel size of the detectors or masks. We propose a shift from pixel-based reconstruction to modal-based reconstruction. Unlike conventional pixels, the resolution in this modal framework is no longer dictated by detector limitations but instead by the inherent optical resolution of the system. This means that basis elements can be generated with exceptionally high fidelity, as they are computed externally rather than being constrained by hardware. By capitalising on the unique properties of tailored light modes, we achieve sharper, more accurate image reconstruction while leveraging modal sparsity to further enhance fidelity. Remarkably, even when the chosen mode set is not strictly orthogonal, effective reconstruction remains possible. We illustrate this using phase-only approximations of the Hermite-Gauss (HG) modes, sidestepping the efficiency losses associated with full complex amplitude modulation. By harnessing modal sparsity, we significantly reduce the number of required measurements, allowing fast image convergence even with a non-orthogonal reconstruction set. The result? High-resolution, high-fidelity quantum ghost imaging of complex objects, achieved faster and with fewer measurements, paving the way for breakthroughs in low-light biological imaging.

Speaker: Fazilah Nothlawala (University of the Witwatersrand)

Physics for Development, Education and Outreach

49 A review of upgrades to First-Year Physics Experiments to integrate digital control and utilization of more modern technology.

Hands-on laboratory work is essential in first-year physics education, yet traditional setups can lack precision and adaptability. In this study, we present upgrades to key first-year experiments (air-track, the simple pendulum, and optics-based experiments), to enhance accuracy, interactivity, longevity and student engagement.

For the air-track and pendulum experiments, we developed a custom Windows-based C# software interfaced with Arduino microcontrollers to automate control and data acquisition. This upgrade improves measurement capabilities and allows for greater experimental flexibility as well as longevity and compatibility. In optics, we replaced filament-based light sources with LEDs, providing more stable and energy-efficient illumination. The spectral characteristics of the different light sources and their implications for experimental results will be presented.

These enhancements offer a more modernized learning experience, fostering deeper conceptual understanding through improved experimental interaction. We will discuss the advantages and challenges of these upgrades, including reliability, ease of use, and student feedback. By integrating modern technology into classical experiments, we aim to bridge the gap between traditional physics education and contemporary scientific methodologies.

Speaker: Dr Hendrik Jacobus van Heerden (University of the Free State)

50 Effects of Learning Environments as Basis for Cognitive Achievements on the Understanding of Basic Physics Concepts

Friendly learning environments have been studied to investigate their effectiveness as the basis of cognitive achievements in the understanding of basic Physics concepts. This is very important when it comes to this notorious subject in terms of difficulty. Students generally believe Physics is a difficult subject, where the challenge is particularly prominent in the first few years of their university experience. This is the stage where students deal with misconceptions about the concepts they need to understand for their success. In an endeavour to deal with this challenge, some lecturers seek ways and strategies for effective methods that could be used to make the delivery of this course easy and manageable for students. A friendly enabling environment was under investigation as one of the methods that was explored in teaching a specific module to a group of first-year students, to enhance their involvement, understanding and ownership of their learning of Physics concepts. This study reports on the findings of this method.

Speaker: Prof. Buyisiwe Sondezi (Department of Physics, University of Johannesburg, Cnr Kingsway Avenue and University Road, Auckland Park, 2006, South Africa)

51 Trends in Mathematical and Physical Sciences Education in South Africa

The South African education system has had difficulties in delivering quality mathematics and physical science instruction to all students, as demonstrated by the nation's performance in international assessments such as the Trends in International Mathematics and Science Study (TIMSS). Almost three decades post-apartheid, the education system still fails to ensure fair access to STEM education, especially in mathematics and physical sciences. This project seeks to investigate and analyze the performance of South African learners in mathematics and physical science, scrutinizing the pre- and post-pandemic school curricula to assess their alignment with 21st-century skills expectations through a data collection method that explores national assessment reports for insights. The investigation concentrated on factors affecting learners' performance in mathematics and science, including teaching quality, resource availability, learners' socio-economic backgrounds, and curriculum and assessment policies. Through the analysis of these aspects, the study sought to elucidate the present condition of STEM education in South Africa and has effectively pinpointed areas necessitating enhancement. This project’s findings further the efforts to improve the quality and accessibility of mathematics and physical science education in South Africa, thereby equipping learners for the challenges and opportunities of the 21st century.

Keywords: Performance, Socio- economy, Pandemic

Speaker: Nthangeni Rofhiwa (University Of Venda)

52 Learning from Kahoot

Kahoot is a popular learning platform with a quiz-show format which is used for a quick review of student knowledge or to provide some variety in how material is presented. It is one of the most popular worldwide with over 70 million users per month. Many papers have been written on the effectiveness on using Kahoot in the classroom but few focused specifically on Physics. In addition most papers focus on formal classroom use of Kahoot, whereas this study took place in an interactive Science Centre (Unizulu Science Centre) and integrated Kahoot with simulations from PhET.
Unizulu Science Centre has served the rural communities surrounding the University of Zululand for almost 40 years. Obtaining feedback and research data from visitors is challenging as contact time is limited. In the past clickers were used to this end but this paper explores using Kahoot instead of clickers and utilising a pre- and post- test format to gather data on student learning. The author extended the clicker-based study performed for his Masters and PhD degrees (and presented at various stages at SAIP Conference) to one utilising Kahoot. Methodology and results will be presented and suggestions made for the effective use of this dynamic tool in out of school settings (like Science Centres) and also in the classroom or lecture theatre.

Speaker: Derek Fish (University of Zululand)

Physics for Development, Education and Outreach

Convener: Mphiriseni Khwanda (University of johannesburg)

Physics of Condensed Matter and Materials

Physics of Condensed Matter and Materials 2

Theoretical and Computational Physics: Session 2

Convener: Prof. Azwinndini Muronga (Nelson Mandela University)

53 A farewell to waves

The wave nature of particles is a notoriously unintuitive feature of quantum theories. However, it is often deemed essential, due to material particles exhibiting diffraction and interference. Troublingly, Lande and Levy-Leblond have shown that de Broglie wavelengths are not relativistically covariant, making any such wave properties physically inconsistent. In this work we explore whether modern experiments vindicate
an alternative view: that apparent waviness in diffraction and interference scenarios emerges as a consequence of quantised interactions between particles. Such a view has historically received very little attention, despite being the exact modern explanation of both the Kapitza-Dirac effect and ultrafast electron diffraction. We study a photon orbital angular momentum realisation of the double slit to prove this explanation capable of unifying quantum interference phenomena.

Speaker: Geoff Beck (University of the Witwatersrand)

54 Quantum Complexity in Neutrino Flavour Oscil- lation

Neutrino flavour oscillation offers a valuable avenue to probe physics beyond the Standard Model. Despite significant progress, key questions remain unresolved particularly the neutrino mass hierarchy and the constraints on parameters governing flavour oscillation, such as the mixing angle θ₂₃ and the Charge-Parity (CP) violating phase δ_CP. In this study, we aim to explore these questions by applying a concept from Quantum Information Theory: quantum complexity.Quantum complexity quantifies the “difficulty” of constructing a given quantum state from a reference state using a set of universal unitary operations (quantum gates). Specifically, we will use Nielsen’s geometric approach to complexity, which focuses on the geometry of the space of unitary operators. In this operator approach, complexity is defined as the minimal geodesic distance from the identity operator to a target unitary. In our case, the target unitary is the time evolution operator governing neutrino oscillation. We first compute the complexity of two-flavour neutrino oscillation, and then extend our analysis to the three-flavour case. We investigate how the oscillation parameters influence the complexity and compare our findings with conventional probabilistic approaches.

Speaker: Luyanda Mazwi (University of Johannesburg)

55 Lorentz Invariant Bell Inequality

Quantum entanglement is a phenomenon in quantum mechanics, whereby the wavefunction of a system of 2 or more particles cannot describe the individual particles separately. What this means in practice is that, in 2 particle systems, for example, if the quantum state of one particle is measured, then the quantum state of the other will be known or there’s statistical correlation between the two measurements. In the case of spin, which is a property of some particles like electrons and positrons that relates to an intrinsic angular momentum, this correlation depends on the detector settings chosen. For example, in a Stern-Gerlach experiment, you have a source of charged spin-1/2 particle pairs created in the centre of the apparatus (which ensures that the spins of each particle in the pair would be entangled due to conservation of angular momentum) and electromagnets on either side. In this Stern-Gerlach experiment, the spin of the particles as measured by Alice or Bob on either side of the apparatus is measured as “spin up” or “spin down” depending on where the path of either particle is bent towards the north or south pole of the magnet. In the case of spin, the correlation would depend on how the electromagnets are aligned with respect to each other. For example, if the measurement settings are parallel to each other, you would get total anti-correlation (i.e. if Alice measures a spin up on her particle, there is 100% probability that Bob will measure spin down on his). It turns out though that the correlations predicted by quantum mechanics cannot be explained classically under reasonable assumptions like locality (i.e. information cannot travel faster than light) and realism (that the particles have definite states whether or not they are measured). This was initially shown in a paper by John Bell in 1967, where starting with the assumptions of locality and realism, he derived an inequality that any such classical correlation should obey, however quantum mechanics predicts that this inequality can be violated which thus proves that if quantum mechanics were correct then one of Bell’s starting assumptions must be incorrect. Later experiments by Anton Zeilinger and Alain Aspect etc, nonetheless confirmed the predictions of quantum mechanics in the case of spin. The original Bell’s inequality and the experiments afterwards only took into account non-relativistic quantum mechanics though. However, from 1997 onwards, there have been theoretical developments showing that the usual Bell variables are not Lorentz invariant, meaning that 2 observers in 2 different inertial reference frames might disagree on whether or not Bell’s inequality is violated. This is due to a relativistic effect called Thomas rotation. Previous authors on the topic suggest the fact that the usual Bell variables are not Lorentz invariant could cause problems in practical applications that require the violation of Bell’s inequality in order to work (such as quantum key cryptography, for example. Thus there have been attempts to define Lorentz invariant Bell variables. Those previous attempts usually involved modifying the the Bell variables in a way describes how to modify the detector settings to get the maximal violation in the lab frame. This may not practical, so we came a different approach that in involved proving a new inequality combining different instances of Bell variables in such a way that the effect of Thomas rotation cancels out thereby making this combination of Bell variables Lorentz invariant. In this presentation, this new Bell inequality will be presented.

Speaker: Mr Jonathan Hartman (University of Johannesburg)

12:30 PM Breather

12:35 PM Lunch

1:45 PM Breather

Plenary

2:35 PM Breather

Applied Physics

Convener: Ernest van Dyk (NMU)

56 Design of an INVELOX based wind delivery system for low wind speed application.

Features such as the omni directional intake, the nozzle-diffuser section as well as the diffuser section of the Increased velocity (INVELOX) wind delivery system augment incident air to a cut in wind speed of most small-scale wind turbines systems. Despite these properties, the INVELOX delivery systems suffers from adverse pressure gradient leading to flow separation within the throat section. This significantly reduces the suction capacity of the intake thus diminishing aerodynamic performance of the system. Amid other scholars that have researched to improve it, this study modified the original INVELOX setup by employing a multi-element diffuser section. The aim is to improve the expansion area and subsequently avoid flow separation on the diffuser wall. The geometry was developed and simulated in an OPEN FOAM environment where the effect to the performance of the INVELOX system as well as the extractable power is then observed. The results show an improved pressure gradient leading to the flow attaching for longer periods within the diffuser. A good value of H/D was shown to improve the speed up ratio of the throat thus emphasizing the importance of a careful design of the diffuser vanes.

Speaker: Anesu Chitura (University of Fort Hare)

57 Quantum state reconstruction on a quantum computer

Quantum state tomography is an essential technique for characterizing quantum systems. It involves performing projective measurements and computationally reconstructing the density matrix from the measurement data by solving a system of linear equations. The discovery of the HHL algorithm has sparked significant interest in leveraging quantum computers to solve these equations, promising a quantum advantage. However, current quantum computers are limited by noise and constrained qubit counts—which restricts effective error correction—rendering the HHL algorithm impractical in the near term. In this work, we propose a hybrid classical-quantum approach using variational quantum eigensolvers (VQEs) for efficient state reconstruction.

Speaker: Mwezi Koni (university of the witwatersrand)

58 Benchmarking Quantum Phase Recognition with a Novel Quantum Convolutional Neural Network

Recognizing quantum phases of matter is a central challenge in quantum many-body physics and quantum machine learning. In this work, we introduce a Novel Quantum Convolutional Neural Network (No-QCNN) architecture tailored for efficient quantum phase recognition and benchmark its performance on IBM’s superconducting quantum hardware. The No-QCNN leverages translationally invariant circuit motifs and entangling layers inspired by classical convolutional networks, adapted to operate natively on near-term quantum devices. We implement and evaluate No-QCNN using quantum circuits composed of parameterized single- and two-qubit gates, trained variationally to distinguish between distinct quantum phases in prototypical spin models, including the transverse-field Ising model. Benchmarking is performed both in ideal simulation and on real IBM Quantum backends, highlighting the model’s robustness against hardware noise and circuit depth constraints. Our results demonstrate that No-QCNN achieves high phase classification accuracy with reduced circuit overhead compared to standard quantum neural network baselines, making it a promising candidate for practical quantum machine learning applications in near-term quantum devices. We discuss implications for quantum phase transition detection, scalability, and future deployment in hybrid quantum-classical workflows.

Speaker: Mr Chisomo Daka (The University of the Witswatersrand)

Astrophysics & Space Science: Space Science Session 2

Convener: John Bosco Habarulema (SANSA)

59 Response of Ionospheric Topside Electron Density during Solar Flares

The topside ionosphere is highly sensitive to solar flare activity, which leads to sudden enhancements
in solar X-ray and EUV flux. These enhancements can significantly alter electron density
profiles, impacting satellite communication and navigation systems. This study examines the response
of topside electron density (Ne) to solar flares using in-situ data from the Swarm satellites.
Electron density measurements during selected solar flare events are compared against X-ray flux
data obtained from the GOES satellite to quantify the degree of ionospheric response. Additionally,
background Ne values from the International Reference Ionosphere (IRI) model are employed to
distinguish flare-induced perturbations from normal diurnal and latitudinal variations. A global
analysis is carried out to investigate the topside ionospheric electron density response across different
latitude regions. Preliminary findings reveal a consistent decrease in Ne during flare events,
with the magnitude of the response varying by local time, latitude, and flare intensity. The study
also explores how the ionospheric response aligns or diverges from IRI predictions during solar
flares.

Speaker: Kenny Monontsi (North-West University)

60 Exploring Long-term trends in total electron content over South Africa

The ionosphere is a dynamic, inhomogeneous and conductive plasma formed from the interaction
of solar Extreme Ultraviolet (EUV) and X-ray radiation with the quasi-neutral atmosphere of the
Earth, found at 60 –1000 km above sea level. With different peak levels of ionization, it is predominantly
studied by determining the total number of particles that pass through a square meter
area between a ground-based station and a GPS satellite –Total Electron Content (TEC). The importance
of TEC is owed by its effect in radio communication, position, telemetry and tracking.
An abundance of free electron gas in the ionosphere causes a delay of signals in the radio band.
This study explores the long-term trends in TEC over South Africa at 2 GPS stations located 1000
km apart. TEC was computed using the IONOLAB software over SUTH and HRAO stations for a
period of 25 years. The TEC trend analysis was performed using 3 solar proxies (sunspot numbers,
MgII and F10.7). Preliminary results show a negative TEC trend between 1998 and 2023 over these
mid-latitudes stations in South Africa. This is consistent with related global studies reported in
the literature.

Speaker: Modiri Mokaila (North West University)

61 Investigation of Altitude and Solar Cycle Variation of DDM Occurrence Using Ionosonde Observations

The diurnal variation of plasma density in the ionosphere is largely characterized by a single peak
around local noon. However, diurnal double maxima (DDM) is sometimes observed when two
distinct peaks and one valley in plasma density appear during the local daytime. Understanding
DDM structures is essential for studying ionospheric dynamics and their key drivers, including
neutral winds, E ×B drift, and solar irradiation, as these variations impact radio wave propagation
and space weather forecasting. This study investigates DDM occurrences using ionosonde
observations from stations in Hermanus (34.4◦S, 19.2◦E, magnetic latitude: 42.08◦S) and Grahamstown
(33.3◦S, 26.5◦E, magnetic latitude: 41.06◦S) during solar cycle 24 (2008–2019). A robust automated
algorithm was developed to detect DDMs based on the presence of two fully formed peaks
separated by a depletion (valley), all occurring between local sunrise and sunset. The algorithm
established the criteria using a minimum peak-to-valley ratio of at least 6% to ensure significant
peak prominence, a minimum peak-to-peak interval of 40 minutes to capture the time difference
between two peaks, and an extra peak prominence threshold not exceeding 5% to filter out additional
peaks. These thresholds ensure that only well-defined DDM structures are identified. The
method was validated through visual inspection, achieving a detection accuracy of 97%. Using
this approach, we identified 1,532 and 1,270 DDM events at Hermanus and Grahamstown from a
total of 3,534 and 2,835 observation days, respectively, over the whole solar cycle. This translated
to an occurrence rate of 43% at Hermanus and 45% at Grahamstown. We will explore statistical
trends in terms of seasonal and solar cycle variations for each ionosonde station. Comparing and
contrasting the trends between the stations may provide indications about possible mechanisms
influencing DDM development. Furthermore, we will explore whether there are DDMs that are
common between the two stations, as this may indicate the scale size and/or propagation of these
events.

Speaker: Fanelesibonge Khoza (University of KwaZulu Natal)

Nuclear, Particle and Radiation Physics-1

Nuclear, Particle and Radiation Physics-2

62 Overview of the current status of the High Granularity Timing Detector for the ATLAS phase 2 upgrade

The increase of the particle flux (pile-up) at the HL-LHC with instantaneous luminosity up to $L ≃ 7.5 × 10^{34} cm^{−2}.s^{−1}$ will have a severe impact on the ATLAS detector reconstruction and trigger performance. The end-cap and forward region where the liquid Argon calorimeter has coarser granularity and the inner tracker has poorer momentum resolution will be particularly affected. A High Granularity Timing Detector (HGTD) will be installed in front of the LAr end-cap calorimeters for pile-up mitigation and luminosity measurement. The HGTD is a novel detector introduced to augment the new all-silicon Inner Tracker in the pseudo-rapidity $\eta$ range from 2.4 to 4.0, adding the capability to measure charged-particle trajectories in time as well as space. Two silicon-sensor double-sided layers will provide precision timing information for minimum-ionising particles with a resolution as good as 30 ps per track in order to assign each particle to the correct vertex. Readout cells have a size of 1.3 mm $\times$ 1.3 mm, leading to a highly granular detector with 3.7 million channels. Low Gain Avalanche Detectors (LGAD) technology has been chosen as it provides enough gain to reach the large signal over noise ratio needed. The requirements and overall specifications of the HGTD will be presented as well as the technical design and the project status. The R&D effort carried out to study the sensors, the readout ASIC, and the other components, supported by laboratory and test beam results, will also be presented. Finally, the involvement of the ATLAS Wits/ICPP group in several HGTD activities will be discussed.

Speaker: Rachid Mazini (School of Physics, The University of the Witwatersrand)

63 Ongoing validation of the High Granularity Timing Detector (HGTD) demonstrator for the ATLAS phase II upgrades

The High Granularity Timing Detector (HGTD) demonstrator was developed to validate the design and performance of its components. The setup included a printed circuit board (PEB), 54 modules, flex tails, a cooling system, and a data acquisition (DAQ) server. Tasks performed involved connecting flex tails, conducting alignment and I2C tests, and performing scanning tests to check bump connections. Threshold voltage (Vth) scans were conducted with high voltage (HV) off at different injected charge values to verify electrical contact between readout electronics and the sensor. Module tuning and charge scans were performed by analysing the time-over-threshold (TOT). A comparison of Vth scans with HV both off and on was done to validate module performance. I2C test failures and high voltage issues, such as large leakage current causing modules to turn off, were identified. Furthermore, clock jitter measurements and calibration methods, mitigating pile-up effects in the forward region, were intended to ensure that the detector’s timing capabilities meet specifications and to identify potential issues with clock distribution or signal integrity. In parallel, work progressed on the second-generation demonstrator, incorporating a slice of the prototype vessel with final design features and an increased number of active components to further refine and validate the HGTD design and its integration aspects, such as the Faraday cage.

Speaker: Thabo James Lepota (School of Physics and Institute for Collider Particle Physics, University of the Witwatersrand)

64 pQCD energy loss calculation for small systems

Shortly after the Big Bang, the universe was in an incredibly hot and dense state, with particles moving at nearly the speed of light. During this brief period, lasting only a few microseconds, quarks and gluons were the dominant components. Due to the extremely high temperatures, these quarks and gluons—collectively known as partons—were only loosely bound and could move freely, forming a state called the quark-gluon plasma (QGP).

The QGP can be recreated in high-energy collisions at large particle colliders such as the Large Hadron Collider (LHC) at CERN. This is achieved by accelerating heavy ions, such as lead (Pb) and gold (Au), to trillions of electron volts (eV) before colliding them, resulting in an extremely hot state where matter dissolves into a QGP. This state cools rapidly, hadronizing within approximately 10 fm/c as quarks and gluons recombine into particles such as pions, kaons, protons, and neutrons. Physicists study the QGP to gain valuable insights into the conditions of the early universe and to better understand the fundamental building blocks of matter.

Jet quenching—the energy loss of high-energy partons traversing the QGP—is well-studied in large systems such as heavy-ion (AA) collisions. However, the observation of QGP-like signatures in small systems, such as proton-nucleus (pA) collisions, poses intriguing challenges. Current jet quenching models, such as the Gyulassy-Levai-Vitev (GLV) formalism, rely on several approximations valid for large systems, including the assumption of large separation distances between scattering centers. Extending these models to small systems requires re-evaluating these approximations in the context of energy loss formalisms.

This project aims to address these challenges by systematically relaxing key assumptions in the GLV framework to develop a more precise understanding of quenching in small systems. Specifically, we investigate transverse momentum broadening in the QGP using the GLV formalism. The primary goal is to determine the momentum distribution of a parton (quark or gluon) traveling through the QGP, focusing solely on broadening effects while excluding radiation.

The GLV formalism is a perturbative expansion in the number of scatterings, allowing for the systematic calculation of any finite number of scatterings. The standard GLV approach employs the eikonal approximation and the large separation distance approximation to simplify calculations. In this work, we relax the large system size approximation by incorporating all path length corrections into the GLV formalism, accounting for energy loss across all system sizes. Additionally, we relax the eikonal approximation by calculating next-to-leading order (NLO) corrections, which involve relaxing the assumption that $E^+$ is the dominant energy scale in the interaction and computing the corresponding correction terms.

We proceed by computing both the single scattering matrix element ($\mathcal{M}_1$) and the double scattering matrix element ($\mathcal{M}_2$). These results are then used to evaluate the color trace, which in turn allows us to compute the full momentum broadening distribution. Finally, we run numerical simulations to compare our theoretical predictions with experimental data, providing a deeper understanding of transverse momentum broadening in different system sizes.

Speaker: Dario Van den Berg (University of the Witwatersrand)

Photonics: Optical Communications & Neural Networks

Convener: Gurthwin Bosman (Stellenbosch University)

65 Crafting Optical Neural Networks Using Multimode Fibre

The utilisation of mode division multiplexing, where multiple spatial modes transmit data simultaneously, holds significant promise for enhancing bandwidth in free space optical communication systems. However, atmospheric turbulence can compromise the reliability of these systems. To address this longstanding problem, traditional neural networks have been employed to classify modes in turbulence. However, these neural networks face challenges relating to energy efficiency, computational speed, and latency. In contrast, optical neural networks offer a potential solution by providing the computational capabilities of traditional networks while mitigating these limitations. In our approach, modal crosstalk within a multimode fibre acts analogously to the weighted sums performed by each layer in a traditional neural network. We demonstrate how an all optical neural network can be built using a multimode fibre and can be used to classify optical modes in turbulence.

Speaker: Christopher Rawlings (The University of the Witwatersrand)

66 Manipulating Modes in Mulitmode Fibres with Magnets

The Faraday Effect, a magneto-optic phenomenon, causes the rotation of linearly polarised light when subjected to a magnetic field along the direction of propagation. In magneto-optic materials like multimode fibres, where different spatial modes interfere to form complex speckle patterns, could these modes be influenced by applying an external transverse magnetic field to the multimode fibre? By utilising different fibre types, including single-mode and step-index multimode fibres, and employing a physics-informed neural network (PINN) to reconstruct the transmission matrix under a magnetic field, we experimentally demonstrate a mode-dependent Faraday Effect in multimode fibres, a new and unexpected result.

Speaker: Mohammed Raiyan Sharif (University of The Witwatersrand)

67 Deep Learning the Digital Twin of Bent Optical Fibre.

Physical perturbations (bends) in optical fibre cause mode-mixing: energy coupling and interference between the fibre's (otherwise propagation invariant) eigenmodes. This mode-mixing can be described using a complex transmission matrix (TM). The ability to predict the effect of physical bends on the TM can help improve mode division multiplexing, imaging, and endoscopy; furthermore, it enables more efficient wavefront modulation via TM engineering, which has applications in optical machine learning and optical quantum circuit construction. Accurately modelling the effects of bends analytically or numerically is non-trivial due to non-linear interdependence between bends. Convolutional neural networks have been used to create optical digital twins: models which predict the impact of bends on the propagating wavefront. Current optical digital twins simply generate images of the predicted output field given an input field (image) and the bend information. This approach fails to describe the TM directly and relies on extensive training to accurately capture physical trends. We investigate the suitability of a new deep learning approach for optical digital twins: physics-informed neural networks (PINNs). PINNs create a compressed model of physical phenomena within the neural network by explicitly encoding physical relationships into the model's architecture and cost function. We design a PINN to directly predict the TM of a bend fibre while ensuring adherence to the law of conservation of energy. The PINN is compared to a traditional neural network in terms of output prediction accuracy, convergence rate, and number of neurons required.

Speaker: Joshua Jandrell (University of the Witwatersrand)

Physics for Development, Education and Outreach

Convener: Mark Herbert (University of the Western Cape)

68 Attitudes and Approaches to Problem Solving as Predictors of Physics Achievement Among First-Year Students

Students’ success in physics is influenced not only by their content knowledge but also by their attitudes and approaches to problem solving. This study investigates the correlation between first-year mainstream physics students’ attitudes and approaches to problem solving and their academic achievement in the subject. A sample of 100 first-year students from the Department of Physics and Astronomy at the University of the Western Cape participated in the study. Students completed the Attitudes and Approaches to Problem Solving (AAPS) survey, and their responses were compared to their performance on a curriculum-aligned physics assessment designed to evaluate conceptual understanding and procedural skills. The findings reveal a moderate to strong positive correlation between students’ problem-solving attitudes and their academic performance, suggesting that those who adopt more expert-like approaches—such as drawing diagrams, reflecting on their solutions, and persisting through challenges—tend to achieve better results. These outcomes underscore the importance of fostering productive problem-solving mindsets alongside traditional content instruction. The study offers valuable insights for improving teaching strategies, curriculum design, and learner support within South African physical sciences education.

Speaker: Mark Herbert (University of the Western Cape)

69 Pre-service students’ misconceptions about simple electric circuits.

Despite all the efforts made by Physics Education Researchers in terms of strategies to enhance students’ conceptual understanding of electric circuit phenomena, students still have conceptual difficulties related to solving problems related to electric circuits. The difficulty is worsened by the presence of misconceptions about electric circuit phenomena. In terms of constructivism, the preparation for teaching should start with identifying what students know prior to instruction. In line with this pedagogy, the research reports on the identified misconceptions as studied from the pre-service students. A report on how these challenges were addressed during the intervention will also be highlighted

Speaker: Mphiriseni Khwanda (University of johannesburg)

70 Reimagining Curriculum Renewal: A case study of Physics and Astronomy

This study provides an introduction to the University of the Western Cape case study on curriculum renewal. It explores different conceptions of curriculum and curriculum renewal. It offers a critique of existing thinking about curriculum renewal as something that occurs within refined phases within the education system, where the thinking often sees curriculum renewal as occurring through linear and hierarchical chains of command from policy to practice. Drawing upon previous conceptualizations of curriculum renewal at the Faculty of Natural Sciences of the University of the Western cape, this study explores a bottom-up approach to curriculum renewal. A rather non-linear process, framed around the concept of intertwined phases of engagements within the higher education system and national imperatives, noting that disciplinary actors, social actors and organizational bodies envision curriculum in different ways for different historical, political, sociocultural and economic reasons. The study contradicts widespread perceptions of the curriculum as a text designed by government official authorities to be implemented in the institutions. It illustrates how the physics and astronomy curriculum renewal involves dynamic processes of interpretation, mediation, negotiation and institutional quality assurance processes across multiple departments and interconnected discipline-applicable arrangements.

Speaker: Bako Nyikun AUDU (University of the Western Cape)

Physics of Condensed Matter and Materials

Physics of Condensed Matter and Materials 2

Theoretical and Computational Physics: Session 3

Convener: Dr Tshegofatso Tshipi (Sol Plaatje University)

71 Classical and Quantum Mechanics of Non-holonomic Constraints

Modern classical and quantum physics is based on Hamilton's variational action principle. Holonomic constraints, constraints that depend on coordinates alone, can be incorporated into a modified Hamilton's variational action principle through the use of Lagrange multipliers. Non-holonomic constraints, those that depend on coordinates and velocity, such as rolling without slipping, have for 180 years eluded a variational action formulation. We present first results on incorporating non-holonomic constraints into a variational action principle and discuss the implications for classical and quantum mechanics.

Speaker: William Horowitz (University of Cape Town)

72 Solving the one-dimensional Schrodinger equation using a set of Daubechies wavelet scaling functions.

In this contribution basis sets derived from Daubechies wavelets scaling functions[1] are used to solve the one-dimensional Schrödinger equation on the interval $[-x_{\rm max}:x_{\rm max}]$. We present the results for
a) the harmonic oscillator and b) the Morse potential as function of the number $N$ of intervals. Double logarithmic fits of the energy error against $N$ are also shown. Fast convergence is found.
Finally further applications to the three-dimensional Schrödinger equation also with a view to density functional calculations are discussed.

References
1.Daubechies,I.(1988). Orthonormal bases of compactly supported wavelets
Communications on Pure and Applied Mathematics, 41(7), 909-996

Speaker: Obiageli Ezenwachukwu

73 Analytical Regularization

We present a novel regularization scheme in quantum field theory, analytic regularization. In our regularization scheme, we modify the action such that convergence is guaranteed before quantization. In particular, using Riesz derivatives, we analytically continue the power of the kinetic term in the action leading to an analytic continuation of the power of the propagator. This power is then treated as the parameter that regulates the UV divergences of the theory. It is a regularization scheme in quantum field theory that modifies the power of the propagators of a theory. We explicitly demonstrate how our scheme self-consistently regularizes massless and massive $\phi^4$ theory and, time permitted , discuss the consistency of our regularization scheme in gauge theories and their related Ward identities.

Speaker: Jarryd Bath (University of Pretoria)

3:40 PM Afternoon Tea

Applied Physics

Convener: Trevor Derry (Wits)

74 Deep Learning for High Throughput Decision Making on Diamond Content of PET Activated Kimberlite Rocks

The MinPET research team is developing novel computer-vision capabilities for crushed rock sorting in diamond mines. Traditional diamond extraction methods employ multi-stage rock-crushing where stages are chosen such that a mine's diamond-size distribution is balanced against the crush size at each stage so that an overall acceptable rate of diamond breakage is maintained. Positron emission tomography (PET) techniques can be used to reconstruct a density map of the distribution of PET isotopes within the rock. PET isotopes in diamond ores such as kimberlite can be activated with a high energy gamma ray beam, and can penetrate to a depth of more than 30 cm. An upper bound of 10 to 15 cm on the crush size is given by the attenuation of 511 keV gammas in the rock. This sorting capacity decreases the rate of diamond breakage. Computer-vision and deep-learning methods can produce autonomous agents capable of on-the-fly decision making, these agents can then identify which rocks contain diamonds and extract them for further careful processing. The expected mass ratio of kimberlite to diamond is about a few billion to 1, thus a fairly accurate agent can reduce processing needs by at least 1000 times, we aim to reduce it by 10,000 times. This talk describes the combination of synthetic data generation and AI training needed to create such agents and outlines our current achievements.

Speaker: Mr Nicholas Connell (University of Johannesburg)

75 Density Functional Theory Study of Azo Dye Molecules Adsorbed onto Anatase TiO2 (112) Surface for Application in Dye-Sensitized Solar Cells

The escalating costs of fossil fuels and the finite nature of accessible reserves the indispensable need of studying alternative energy sources. Organic solar cells present a practical and economical technology for capturing solar energy, utilizing materials that are often both accessible and recyclable. Conventional silicon solar cells demonstrated significant reliability; however, their costs remain a barrier. Dye-sensitized solar cells (DSSCs) present a compelling alternative at a significantly reduced cost. In this study, density function theory has been used to explore the adsorption behavior of synthetic dye on the surface of (1 1 2) TiO2 anatase polymorph. Generalized gradient approximation was used to define the exchange-correlation function within the scheme of Perdew-Burke Ernzerhof as implemented in the Material Studio.The effectiveness of the dye-sensitized solar cell is dependent upon the electronic configuration of the dye-sensitizer and its excitation properties. Our results show the UV-Vis absorbance of Azo dye 1, Azo dye 2, Azo dye 3 and Azo dye 4 at 570 nm, 428 nm, 439 nm, and 648 nm, respectively, along with a calculated light harvesting efficiency of 51.3%, 29.5%, 50.58%, 74.8%, respectively. Among the computed four Azo dyes, the results indicate that Azo dye 4 has a stronger sensitization capability relative to the others, with a small HOMO-LUMO gap. Furthermore, the band gap of the anatase is reduced after Azo dye adsorption. The calculated adsorption energies are found to be negative, implying that Azo dyes molecules are electron-donating substituents, and strongly bind strongly to the anatase surface.
Keywords: Azo dyes, semiconductor, band gap, density functional theory, Dye-sensitized solar cells, TiO2

Speaker: Ronel Ronella Randela (University Of Venda)

76 DFT Study of the (210) TiO₂ Brookite Surface Doped with V and Zr for Application in DSSCs

Dye-sensitized solar cells (DSSCs) present a promising photovoltaic technology due to their cost-effectiveness, high efficiency, and flexible device design. DSSCs generally use titanium dioxide (TiO₂) as a photoanode material. Brookite TiO2 phase provides special electrical characteristics fit for maximum solar energy conversion. However, the broad bandgap of bulk TiO₂ limits its absorption in the visible light range.
In this work, density function theory has been used to explore the properties of (210) TiO₂ brookite surface doped with vanadium (V) and zirconium (Zr). Generalized gradient approximation was used to define the exchange-correlation function within the scheme of Perdew-Burke Ernzerhof, as implemented in Material Studio. The results show that doping greatly lowers the energy bandgap of TiO₂ Brookite (210) surface, therefore improving the visible light absorption. Also, doped surfaces show less reflectance, desired for light harvesting. From computation of formation energies, the stability of the doped systems is verified as V and Zr dopants efficiently integrate into the TiO₂ surface without sacrificing structural integrity. The study reveals that Vand Zr doping enhances the optical and electrical characteristics of the TiO₂ Brookite (210) surface, therefore offering a suitable material for effective DSSC uses.
Keywords: Semiconductor, band gap, density functional theory, dye-sensitized solar cells, TiO2 brookite.

Speaker: Tshifhiwa Ranwaha (University Of Venda)

77 VOLITALIZATION OF FLAME RETARDING COMPOUNDS FROM FIREFIGHTER BUNKER GEAR USED IN SOUTH AFRICA DUE TO THERMAL EXPOSURE

Firefighting bunker gear provides the first line protection for firefighters during fire conditions. The protective garment is fabricated from superior performance fibres and enhanced by the addition of flame retardants (FRs), which resist ignition and delay flame spread. Flame retardants have been attributed to 15-fold greater escape time for occupants. However, concerns have been emerging on the potential harmful effects of some flame retardants, particularly the brominated flame retardants (BFRs). The BFRs usage have been banned in many countries and are also listed in international treaties as harmful to human and the environment. This study investigated the presence of BFRs concentration in bunker gear, particularly polybrominated diphenyl ethers (PBDEs) and their congeners in the garment and evaluate their impact on thermal performance.

Five different types of bunker gear were tested for the volatilization of the BFRs due to heat exposure. The cone calorimeter was used to expose samples to heat flux of 3, 5, 6 and 8 kW/m2 and polyurethane-foam (PUF) disks were suspended above the samples to capture evolving flame retardants. The PUF disks were extracted with solvents and analysed for the target compound with the gas chromatography mass spectrometry (GCMS). In the GCMS, samples were analysed for a number of PBDEs namely BDE-28, -47, -99, -100, -153, -154, and -209. Of the seven congeners analysed, PBDE congeners -28, -47, and -99 were detected in all five sample materials with concentrations from 0.02 to 0.1 ng/g, 0.03 to 0.34 ng/g and 0.18 to 0.86 ng/g, respectively. Congeners -100 and -153 were detected in 80% and -209 in 40% of the samples. BDE-99 was the most abundant compound detected, with concentration ranging between 0.183 and 0.866 ng/g, followed by BDE-47, ranging from 0.03 to 0.34 ng/g. BDE-209 was the least detected in the samples with concentration, ranging from 0.02 to 0.0.23 ng/g. The results from this study indicates the volatilization of BFRs from the firefighter bunker gear during heat exposure.

Speaker: Mr Vincent Mokoana (TUT, Department of Physics)

Astrophysics & Space Science: Radio astronomy

78 Tracing the origin of radio emission in galaxies with MIGHTEE

Pinpointing the true source of radio emission in galaxies is a rather complex task that requires detailed modelling of radio spectral energy distributions. With the recent availability of catalogues of radio sources detected with interferometers such as MeerKAT, uGMRT, and LOFAR, we are able to push down the detectable flux range to the point where we can detect the faintest radio emission in galaxies. At this faint flux end, it is generally unclear which specific mechanisms produce radio emission. In this foundational study, we begin to tackle this quandary by obtaining constraints on spectral curvature using four-band radio detections spanning observed frequencies of 100 MHz - 2 GHz for radio-loud AGN. Considering the Eddington and Malmquist biases which skew our results at low and high radio fluxes, respectively, we find a dominance of steep spectrum sources among the radio-loud active galactic nuclei (AGN) population indicative of synchrotron processes originating from the jets and lobes. For non radio-loud AGN (assumed to be normal star-forming galaxies and radio-faint AGN), we see a predominance of flat spectra associated with thermal processes occurring in HII regions.

Speaker: Sthabile Kolwa (UNISA)

79 Searching for persistent radio emission towards selected Fast Radio Burst positions

Fast Radio Bursts (FRBs) are millisecond-duration radio emissions originating from cosmological distances, as indicated by their large dispersion measures. While numerous FRBs have now been localised to their host galaxies, a distinct class of compact electromagnetic counterpart, the Persistent Radio Source (PRS), has also been identified in some cases. These PRSs, have so far only been found in association with a small number of actively repeating FRBs. Characterising these PRSs is crucial for providing insight into the progenitors, local environments, and evolution of FRBs. Currently, only four repeating FRBs (FRB 20121102A, FRB 20190520B, FRB 20201124A, and FRB 20240114A) have confirmed associations with a PRS. This work presents several potential candidates for PRSs associated with FRBs using data from the MeerKAT Radio Telescope. A comprehensive multi-wavelength approach is necessary to confirm whether these candidates genuinely qualify as PRSs, with the aim of increasing the currently limited sample of known FRB-PRS associations.

Speaker: Mr Thulo Letsele (Centre for Space Research, Potchefstroom Campus, North-West University, Potchefstroom 2520, South Africa)

80 A Search for Transient and Variable Radio Sources in the NGC 5068 field Using MeerKAT MHONGOOSE data.

Transient surveys play a crucial role in understanding the dynamic Universe, with radio transients serving as indicators of explosive and energetic astrophysical events. Despite their importance, conducting commensal radio imaging surveys for transients often demands extensive computational resources, data storage, and processing time. The MeerKAT radio telescope, with its high sensitivity and large field of view, presents an excellent opportunity to explore the transient radio sky efficiently. This study analysed MeerKAT observations of the NGC 5068 field from the MHONGOOSE Large Survey Project (LSP) to search for radio transient and variable sources. The dataset comprises ten distinct epochs, spanning timescales from approximately one month to over a year. The analysis was carried out using the Transients Pipeline (TraP) on the Inter-University Institute for Data Intensive Astronomy (IDIA) cloud computing platform. While no transient sources were detected, we identified 12 variable radio sources within the field.

Speaker: Ms Vhuthu Tshilengo (University Of Venda)

81 MeerKAT view of serendipitously discovered MGCLS GRGs

Giant radio galaxies (GRGs) are peculiar astrophysical objects because of their exceptionally large linear sizes (>0.7 Mpc). The cause for their huge sizes remains a mystery.
We investigate the spectral behaviour of a small sample of seven (7) GRGs detected from the MeerKAT Galaxy Cluster Legacy Survey (MGCLS). These sources have a minimum linear size of 0.723 Mpc to a maximum linear size of 2.209 Mpc. The spectral index analysis reveals steeper spectral indices around the lobes and flatter spectral indices toward the core for most of the sources. In one of our sources (MKT J021309.59-474414.1), we observe a signature of a backflow while in another (MKT J002659.83-121831.3 ) a potential episodic activity. We further confirm that one of our sources is most likely to be found in a cluster environment. We detect a new GRG which is the largest in our sample, with a radio morphology that shows complex features. The source is hosted by an elliptical galaxy with a stellar mass of 7.413$^{+0.222}_{-0.216} \times$ 10$^{11}$ M$_⊙$.

Speaker: Dr Nceba Mhlahlo (University of the Witwatersrand)

Nuclear, Particle and Radiation Physics-1

Nuclear, Particle and Radiation Physics-2

Photonics: Structured Light, OAM & Topology

Convener: Pieter Neethling (Stellenbosch University)

82 Getting to know the elegance of Laguerre-Gauss beams

Laguerre–Gaussian (LG) modes are solutions of the paraxial Helmholtz equation in cylindrical coordinates and are associated with light fields carrying orbital angular momentum (OAM). It is customary to modulate such beams using phase-only vortex profiles, e.g. when increasing (laddering up) or decreasing (laddering down) the OAM content of some given LG mode. However, the resulting beams have been shown to be hypergeometric-Gaussian modes, due to the changing radial amplitudes on propagation. In this work, we show that these beams in fact have the angular spectrum of a set of modes known as elegant Laguerre–Gaussian (eLG) modes, which map back to LG-type modes more intuitively than hypergeometric-Gaussian modes. Accordingly, the fields obtain new OAM and radial quantum numbers that depend on the initial OAM and additional OAM gained during modulation. Identifying the true modal structure of OAM-modulated beams as elegant Laguerre–Gaussian modes improves our understanding of beam evolution and supports more precise control in applications like optical communication, beam shaping, and quantum information processing.

Speaker: Vasili Cocotos (University of the Witwatersrand)

83 Nonlinear modal decomposition of structured light

Structured light, tailored in its degrees of freedom for specific applications, has recently emerged as a highly topical field driven by advancements in both linear and nonlinear optical techniques. This has led to significant progress in nonlinear structured light, with applications spanning holography, spectroscopy, imaging, and even quantum teleportation. These breakthroughs rely on the ability to create structured light at one wavelength while achieving high-fidelity detection at another. While wavelength conversion techniques for generating structured light are well established, detection tools remain in their infancy. Here, we introduce a modal decomposition technique for structured light using nonlinear crystals, enabling full-field reconstruction at one wavelength by using a basis encoded at a different wavelength. In addition, we propose a faster, single-shot reconstruction approach through a nonlinear extension of off-axis holography. We demonstrate both techniques using representative examples of structured light, including orbital angular momentum (OAM) and Hermite-Gaussian (HG) beams. Our nonlinear approach to modal analysis offers the flexibility to choose efficient detectors, effectively removing wavelength constraints in structured light applications. This technique opens up new possibilities for nonlinear structured light, paving the way for future advancements in communication, imaging, and spectroscopy.

Speaker: Sachleen Singh

84 Compensating and keeping up with atmospheric chaos by tailoring beams of light

The ability to tailor light in all of its degrees of freedom has seen significant improvements in the fields of optical imaging and communications. It has allowed for the straightforward implementation of spatial modes of light which can be used to form higher dimensional encoding alphabets to increase the bandwidths of free space and optical fibre channels. The orthogonality and completeness of the mode sets allow them to perfectly describe any 2D complex (amplitude and phase) image. However, the promise of structured light is hindered by the distortions induced by the various complex media through which it often needs to propagate. This has many deleterious effects such as limiting imaging resolution, reducing the range over which we can communicate and increasing modal crosstalk. Many of the proposed solutions to combat the degradation of structured light involve determination of a transmission matrix (TM) which describes the manner in which the channel distorts incident light fields. However, The TM is time consuming and difficult to measure making these techniques challenging to implement. Here, we propose a method for estimating the TM in parallel with sending or receiving data through the channel. This allows for a more realistic implementation of these methods and allows us to update our transmission matrix as the medium evolves in time. We demonstrate this both numerically and experimentally, using atmospheric turbulence as an example. This work has applications in the fields of both quantum and classical imaging and optical communications.

Speaker: Cade Peters (Univeristy of the Witwatersrand)

85 Invariance to Randomness Using the Topology of Light

The topology of light and its robustness to noise has garnered significant interest over the last few years as a promising means of information transfer. Light’s topology, more specifically the Skyrmion topology, describes the correlation between light’s position and polarization. Skyrmions have been shown to be invariant to isotropic noise; whether topology is invariant to random media is investigated. In this work, we investigate classical vector beams and spatially and polarisation entangled photons' reaction to random media. We used digital phase screens to simulate the random media before using real and biological cell samples. We successfully showed that light’s Skyrme number was invariant to all three kinds of random media investigated. For classical vector beams topology was conserved for random media varying in scattering strength. Our work demonstrates topologies robustness to random media and shows exciting promise for its use in real-world information transfer.

Speaker: Tatjana Kleine (University of the Witwatersrand)

Physics for Development, Education and Outreach

86 Assessing First Year Students’ Epistemological Beliefs about Learning Physical Science

Epistemological beliefs individuals hold about the nature of knowledge and learning play a crucial role in understanding and engaging in the physical sciences. These beliefs influence how students, educators, and researchers perceive scientific concepts, theories, and methodologies. In the context of physical sciences, epistemological beliefs encompass views on the certainty and structure of scientific knowledge, the role of empirical evidence, the nature of scientific inquiry, and the evolution of theories over time. While some individuals may see scientific knowledge as absolute and unchanging, others recognize its dynamic and tentative nature, shaped by ongoing experimentation and revision. Research suggests that sophisticated epistemological beliefs, which acknowledge the complexity and evolving nature of scientific understanding, enhance critical thinking, problem-solving, and engagement in scientific discourse. The study shows a slight improvement in the sophistication of epistemological beliefs after intervention using inquiry-based approaches.

Speaker: Dr Paul Molefe (University of Johannesburg)

87 An optical approach to quantum education

Quantum mechanics is an inherently challenging subject to learn and is sometimes counterintuitive. For example, concepts like entanglement, and the wave-particle duality theory oppose classical physics. However, conceptual parallels between quantum systems and classical systems can be exploited to bring intuition and advance the learning process. Classical light fields are one such states that can exhibit properties that are analogous to some properties of quantum states, for example, they also satisfy the wave-particle duality theory. Vector fields are a form of classical light whose spatial mode is coupled to its polarisation state and are said to be non-separable. Mathematically, they are similar to quantum entangled states, that is when two spatially separated particles are correlated, thus, performing a measurement on one particle will affect the outcome of a measurement on the other particle. In this work, the use of quantum tools, like quantum state tomography and Bell-type measurements, is demonstrated on simple classical experiments to draw an intuition of quantum entangled states. We present a low-cost, easily replicable experiment, based on spatial light modulator technology, for laboratories to assist in the study of quantum mechanics.

Speaker: Mr Cathy Maako (University of the Witwatersrand)

88 The role of laboratory demonstrators in the learning and understanding of physics and chemistry concepts

It is almost a common practice in institutions of higher learning that most experimental modules are well executed and understood by students if laboratory demonstrators are actively involved. This involvement is designed to assist students in understanding the practical aspects of their experiments before and during the laboratory session. This work reports on the vital and multifaceted role of laboratory demonstrators at the South African university in making learning effective for the students attending physics and chemistry practical sessions. The roles extend beyond the supervision of practical sessions. Demonstrators serve as key intermediaries between theory and experimental practices, assisting students to grasp abstract concepts through hands-on engagement.

Speaker: Prof. Buyisiwe Sondezi (Rare Earth-Based Oxides and Nano Group, Department of Physics, University of Johannesburg, Cnr Kingsway Avenue and University Road, Auckland Park 2006, South Africa)

Physics for Development, Education and Outreach

Convener: Deena Naidoo (University of the Witwatersrand)

Physics of Condensed Matter and Materials

Physics of Condensed Matter and Materials 2

Theoretical and Computational Physics: Session 4

Convener: Sam van Leuven (University of the Witwatersrand)

89 From Matrices to Spacetime: Probing Symmetry Breaking in the Type IIB Matrix Model

One of the significant challenges in superstring theory is understanding how the extra dimensions of space might shrink down to sizes we cannot see - something called dynamical compactification. The type IIB matrix model is a robust mathematical framework that aims to describe this process in ten dimensions. In this model, space itself is expected to emerge from the behavior of large matrices, which can break the original symmetry of the model. However, studying this model is extremely difficult because of a technical issue known as the sign problem, which arises from complex numbers in the calculations. The complex Langevin method has recently shown success in dealing with this challenge. In this work, we apply this method to explore whether the symmetry in the model is spontaneously broken. Our findings suggest that the complex part of the model plays a key role in triggering this symmetry breaking, helping us understand how space and its structure might emerge from fundamental theory.

Speaker: Dr Anosh Joseph (University of the Witwatersrand)

90 The rich topological tapestry embedded in entangled states

Topology has emerged as a fundamental feature across diverse physical systems, from cosmology and condensed matter to high-energy physics and wave dynamics. Yet, despite its broad relevance, topological studies have largely been confined to low-dimensional classical systems. Here, using entangled quantum states, we uncover a vast landscape of diverse topological maps derived from high dimensional entangled states. By engineering our quantum states to mimic a non-Abelian field in SU(d) Yang-Mills theory, we predict multiple topological structures as mappings between a reference 2-sphere and multiple submanifolds embedded within the high dimensional manifold yielding a topological spectrum of invariants which scales with the dimension of the states. Notably, partitioning this spectrum into trivial and non-trivial components enables simultaneous robustness against perturbations while also serving as a probe for them, achieved by detecting emergent signatures in the initially trivial partition. While the results and analysis are presented using the orbital angular momentum of photonic quantum states as an example the theoretical framework provided is broadly applicable to any particle type, dimension, or degree of freedom. This work opens exciting prospects for quantum sensing and communication through topology.

Speaker: PEDRO DINIS ORNELAS (University of the Witwatersrand)

91 Machine Learning Modular Forms in String Theory

Over the last two decades, automorphic forms have emerged as encoders of the mathematical principles underlying the organization of information and microstates in quantum gravity. Perhaps their most significant appearance in this context lies in the counting of black hole microscopic states. The detection and classification of modular forms—and the analysis of their modular properties—thus offer promising pathways to a deeper understanding of quantum black holes.

In this talk, I will demonstrate how the search for modular symmetries relevant to quantum gravity is highly amenable to ML techniques. I will present preliminary results in this direction by developing ML protocols for classifying modular and Jacobi forms and report on the efficacy of the neural nets employed. I will conclude with remarks on potential applications to black hole microstate counting.

Speaker: Abinash Swain (University of Witwatersrand, Johannesburg, SA)

92 Testing $f(Q)$ gravity as a solution for the $H_0$ and $S_8$ tensions

The persistent discrepancies between early and late universe cosmological measurements of the Hubble parameter ($H_0$) and the matter clustering parameter ($S_8$) pose significant challenges to current physics. In this study, we take into account such discrepancies to solve through the modified theory of gravity known as $f(Q)$ gravity (a symmetric teleparallel) framework where gravity is described by non-metricity $Q$, which offers a promising alternative to resolve these tensions. We will investigate the viability of $f(Q)$ gravity confronting the theory with recent cosmological data sets from both early and late measurements. Our analysis determines whether $f(Q)$ gravity can simultaneously reconcile the tensions of the $H_0$ and $S_8$ parameters while providing a theoretically compelling alternative to the $\Lambda$CDM model. The results provide crucial insights into modified gravity's capacity to address fundamental challenges in modern cosmology.

Speaker: Dumiso Mithi

WAADD

Wed, July 9

Plenary

9:15 AM Breather

Applied Physics

Convener: Trevor Derry (Wits)

93 Amplitude transformation in a qubit register

In quantum computing a diagrammatic representation of a code is conventionally displayed as a vertical column of qubits that feed from left to right into a network of wires and gates. An alternative view is an array with qubits as a header row for all register eigenstates, with amplitude values as a column on the left. In this view, the action of gates on the register is seen as successive transformations of amplitude values, which allows for quantum parallelism to be seen acting on the register as a whole and for the ingenuity of various algorithms to be evident. Examples are the algorithms by Deutsch and for quantum teleportation.

Speaker: Alan Matthews (UKZN)

94 A Comparative Analysis of Radiation-Induced Wavelength Shift in Radiation-Soft and -Hard Fibre Bragg Gratings Exposed to Proton Irradiation

Fibre Bragg Gratings (FBGs) have emerged as highly sensitive sensors for monitoring environmental parameters such as temperature, strain, radiation dose, etc. Moreover, they can withstand extreme environments, of interest here, a high radiation dose environment. The goal of this work is to develop reliable sensing instruments for high radiation-hard environments, such as the ATLAS inner tracker where radiation can go up 20 MGy and in nuclear reactors which require radiation resistance up to at least 1 GGy.

This study presents a comparative investigation of radiation-induced wavelength shifts in radiation-soft and radiation-hard FBGs exposed to proton irradiation at CERN, reaching a cumulative dose of 2.6 MGy over one week. These values are extrapolated to the typical dose that would be received in a two-week to a month run in-core and full-power in a power reactor. The extrapolation is done using Monte Carlo modelling.

The core of the optical fibres consists of SiO2 base material. Dopants such as germanium (Ge), phosphorous (P), fluorine (F), and aluminum (Al) are incorporated into the silica matrix to modify its refractive index. Fibres with pure silica cores, and fluorine-doped cores, have been found to have much higher resistance to ionizing radiation (i.e. radiation-hard) than compared to other dopants.

The results highlight the degradation mechanisms in radiation-soft and radiation-hard FBGs, providing critical insights for their deployment in extreme radiation environments. This work advances the development of robust FBG-based sensors for particle physics, space instrumentation, and nuclear energy systems, where real-time dose monitoring in high-radiation fields is essential.

Speaker: Bongani Maqabuka

95 Listening With Light

Environmental vibrations can induce distortions in live fibre optic cables through the elasto-optic effect, leading to changes to both the light's state of polarisation (SOP) and phase. Coherent optical receivers, essential to modern telecommunications, offset these distortions by employing advanced digital signal processing (DSP) techniques to filter out the effects during high-speed data reception. This presents an interesting opportunity: Why not extract the channels' SOP and phase estimation data from the receiver for environmental sensing purposes? Although SOP and phase estimation data from coherent optical receivers have been used to detect sub-hertz frequency events like earthquakes and tsunamis, their application in acoustic sensing remains unexplored. This study investigates whether these SOP and phase changes, detectable over live data channels using coherent receivers, can be used to sense low-frequency acoustic signals in a controlled laboratory environment. Unlike traditional acoustic sensing techniques, such as Distributed Acoustic Sensing (DAS), which relies on dedicated sensing fibres, this method uses existing data channels and receivers, eliminating the need for additional infrastructure. If successful, this approach could extend existing fibre optic infrastructure capabilities for applications like subsea cable monitoring and urban infrastructure surveillance.

Speaker: Max Brenner (University of the Witwatersrand Johannesburg)

Astrophysics & Space Science: Galaxy clusters

96 Exploring the correlations between galaxy properties and environment in the large-scale structure of the Universe

Galaxies are gravitationally bound systems composed of stars, gas, dust, and dark matter. Various galaxy properties—such as luminosity, stellar mass, and star formation rate—are significantly correlated with their local environment, such as whether they reside in dense clusters or more isolated regions. Understanding these environmental correlations is crucial for studying galaxy evolution within the large-scale structure of the universe. Traditionally, such studies rely on local density measurements defined at a specific separation scale around galaxies. However, to fully capture the impact of environment, it is essential to examine correlations across a wide range of scales. This approach helps investigate environmental effects that operate at different scales while minimising the impact of an arbitrarily chosen density estimation scale.

In this talk, I will demonstrate how marked correlation functions effectively trace the environmental correlations of various galaxy properties as a function of separation scale. I will present results from our studies on the correlations of luminosities (from optical to mid-IR bands), stellar mass, and star formation rate with local environment. Additionally, I will show how marked correlation functions offer advantages over traditional two-point correlation functions in probing the environmental dependence of galaxy mergers. Our analysis is based on stellar-mass-selected, volume-limited galaxy samples from the Galaxy And Mass Assembly (GAMA) survey. We also compare our measurements from GAMA with those from CosmoDC2, a simulated sky catalogue designed for the Rubin Observatory LSST Dark Energy Survey Collaboration. Finally, I will present our recent results on the environmental correlations of low-surface-brightness galaxies (LSBGs) identified in the Dark Energy Survey and North Ecliptic Pole Wide field.

Speaker: Unnikrishnan Sureshkumar (Wits University, Johannesburg)

97 Probing Gas Sloshing in the Core of Galaxy Cluster ZwCl 3146: Insights from Chandra and GMRT Observations

We present an analysis of the X-ray bright galaxy cluster ZwCl 3146 (redshift z = 0.291) using archival 90 ks Chandra observations, along with our 1.4 GHz GMRT observations. Beta model subtracted residual and unsharp X-ray images reveal spiral-like features within the central 230 kpc, indicative of gas sloshing in the intracluster medium (ICM). We also detect an offset of about 11 kpc between the brightest cluster galaxy (BCG) and the X-ray peak, as well as signs of interaction between the BCG and a substructure in the cluster core. These features suggest that the observed sloshing was triggered by a minor merger event. Furthermore, we identify three sharp surface brightness edges to the North-East, South-East, and South-West of the X-ray peak, located at projected distances of 232 kpc, 172 kpc and 119 kpc, respectively. X-ray spectral analysis across these edges reveals temperature jumps, accompanied by electron density discontinuities with an average density compression factor C = 1.46. The pressure profiles remain continuous across these edges, consistent with their interpretation as cold fronts generated by gas sloshing. The GMRT 1.4 GHz image reveals the presence of a central radio source, along with diffuse radio emission co-spatial with the central spiral structure. The radio emission partially fills some of the previously reported X-ray cavities.

Speaker: Satish Sonkamble

98 The ACT Data Release 6 Sunyaev-Zel'dovich Selected Cluster Catalog

The Atacama Cosmology Telescope (ACT) conducted an arcmin resolution survey of the southern sky at millimetre wavelengths from 2008-2022. In this talk I will present an update on the ACT search for galaxy clusters using the redshift independent Sunyaev-Zel'dovich (SZ) effect, using data from the full ACT survey, covering 15,000 square degrees. The final ACT Data Release 6 (DR6) cluster catalog is expected to include more than 9,000 galaxy clusters with redshift and mass estimates. I will describe the construction of the catalog (in particular the differences with respect to ACT DR5), products and tools associated with the data release, and discuss some science applications of the catalog.

Speaker: Matt Hilton (University of the Witwatersrand)

Nuclear, Particle and Radiation Physics-1

99 Systematics study of ground-state bands in rotating even-even nuclei to reveal triaxial deformation at ground state

The question of whether atomic nuclei can have triaxial shapes at their ground states is still an ongoing subject of debate. In this study, we systematically analyze the ground-state bands of rotating even-even nuclei to identify the presence of triaxiality across the nuclear chart using experimental data. We apply the newly proposed Coriolis analysis method, which involves plotting $E_{\gamma} = E(I) - E(I-2)$ as a function of spin $I$. Of particular interest is the value $I_c$ at which the curve crosses the x-axis. Using this method, we analyzed over 600 deformed even-even rotating nuclei and obtained results for 268 of them. The results show that these nuclei exhibit three distinct shapes: axially symmetric, stable triaxial, and $\gamma$-unstable shapes. A comparison of these theoretical and our experimental results, predicted by different models like the FRLDM calculations, shows that several hundred nuclei are affected by triaxiality [1]. A good agreement was found between the theoretical and experimental results, providing further evidence that the proposed approach is reliable. The analysis provides detailed information about the nuclear shapes associated with the nuclear ground-state band, helping determine whether the shape is axially symmetric or triaxial. The results of this work will be discussed at the South African Institute of Physics conference.

[1] P. M¨oller, R. Bengtsson, B.G. Carlsson, P. Olivius, and T. Ichikawa. Global calculations of ground-state axial shape asymmetry of nuclei. Phys. Rev. Lett., vol. 97, p. 162502, Oct 2006. URL https://link.aps.org/doi/10.1103/PhysRevLett.97.162502.

Speaker: Nkonzo Xulu (University of Zululand)

100 Study of the K quantum number of pygmy states in 154Sm

This study aims to investigate the Pygmy Dipole Resonance (PDR) in the deformed ¹⁵⁴Sm nucleus. The present study employs the ( γ , γ ′) reaction to examine dipole states in the energy range 3.5 MeV to 7.05 MeV (close to the neutron separation threshold (8 MeV)). The experiment was carried out using the Clover Array at the HIγS facility of the Triangle Universities Nuclear Laboratory. The polarised beam produced at the facility enables measurements through the asymmetry method to characterize the nature of populated transitions, allowing differentiation between 1^- and 1⁺ states, an essential aspect in the study of the dipole response of nuclei. Furthermore, the high-resolution beam mode (< 2%) available at HIγS makes the determination of the decay branching ratio to the first 2⁺ state possible. This will aid in identifying the K quantum number of various excited states and in analyzing the PDR as a function of excitation energy. The validity of the Alaga rules in the region of the PDR will also be investigated in this work. The motivation behind this study, along with experimental details, will be presented. Preliminary data analysis will be discussed and an outlook on future comparisons will be provided.

This work is based on the research supported in part by the National Research Foundation of South Africa (Grants No. MND210503598725, No. REP_SARC180529336567) and the US Department of Energy (Grants No. DE-FG02-97ER41041 (UNC), No. DE-FG02-97ER41033 (TUNL)).

Speaker: Refilwe Emil Molaeng (University of the Witwatersrand and iThemba LABS)

101 Nature of the low-spin states in the moderately-deformed triaxial ¹⁹³Au nucleus

Unlike axially symmetric nuclei, triaxial nuclei give rise to exotic collective phenomena, such as nuclear wobbling and chirality—topics that have garnered significant attention in recent years. These phenomena not only challenge our understanding of nuclear deformation, but also enrich the landscape of gamma spectroscopy with distinctive signatures that demand both experimental and theoretical exploration. It has been recently proposed that odd-mass triaxial nuclei can exhibit wobbling motion even at low spins [1]. Excited bands interpreted as wobbling modes have been reported in several nuclei, including the gold isotopes ¹⁸³Au and ¹⁸⁷Au, which are excellent candidates for studying such phenomena due to the presence of triaxial shapes in this mass region [2,3].
In ¹⁸³Au, an excited band built on the h_9/2 configuration was associated with transverse wobbling, where the odd proton aligns along the short nuclear axis [4]. In contrast, ¹⁸⁷Au showed evidence for longitudinal wobbling, with the odd proton aligned along the intermediate axis [5]. This difference in the angular momentum alignment of the valence proton in these two isotopes is particularly intriguing, as their proton Fermi levels are expected to be similar. The strongest experimental evidence supporting the wobbling interpretation was based on the evaluated large mixing ratios of the transitions linking the excited and yrast h_9/2 bands. However, a recent remeasurement of these mixing ratios in ¹⁸⁷Au revealed a dominant M1 component [6], which rules out the earlier proposed wobbling interpretation. These contrasting findings highlight the challenges of such measurements and underline the need for further investigations—particularly in the gold isotopes.
In the present study, low- to medium-spin excited states of ¹⁹³Au were investigated using the tape station setup at iThemba LABS. These states were populated via β-decay following the ¹⁹⁷Au(p,5n)¹⁹³Hg reaction at E_p = 50 MeV. The resulting gamma rays were detected with three Compton-suppressed clover detectors and one Compton-suppressed segmented clover detector. In addition, a Si(Li) detector was used to measure internal conversion electrons. These measurements allowed us to explore the interplay between single-particle and collective excitations in bands based on the h_9/2 and h_11/2 configurations at low to medium spin. Various techniques were employed to extract multipole mixing ratios and assign spins and parities to the observed states. Furthermore, Quasiparticle plus Triaxial Rotor (QTR) calculations were performed to characterize the nature of the excited states.
[1] S. Frauendorf et al., Physical Review C 89.1 014322 (2014):.
[2] E.A. Gueorgieva et al., Phys. Rev. C 64, 064304 (2001).
[3] E.A. Gueorgieva et al., Phys. Rev. C 69, 044320 (2004).
[4] S. Nandi, et al., Phys Rev Lett 125.13, 132501 (2020).
[5] N. Sensharma, et al., Phys Rev Lett 124.5, 052501 (2020).
[6] S. Guo, et al., Phys. Lett. B, 828, 137010 (2022).

Speaker: Sinegugu Mthembu (University of the Western Cape & iThemba LABS)

102 X-ray production cross section measurements for the analysis of metal halide perovskite thin films using heavy ion PIXE spectroscopy

X-ray production cross section measurements for the analysis of metal halide perovskite thin films using heavy ion PIXE spectroscopy

M.L. Moremi¹, M. Msimanga^{1, 2}, M.C. Masekane^{2, 3}

¹ Department of Physics, Tshwane University of Technology, Private Bag X680, Pretoria,001, South Africa

² iThemba LABS TAMS, National Research Foundation, P Bag 11, WITS, 2050, Johannesburg, South Africa

³ Ruđer Bošković Institute, P.O. Box 1016, 10000, Zagreb, Croatia

Moremilily@gmail.com, Msimangam@tut.ac.za, Masedi.Masekane@ilabs.nrf.ac.za

Abstract.

The use of perovskites for the development of solar cell devices continues to gain traction due to their high light absorption efficiency and tuneable bandgap. Unfortunately, well studied high efficiency organic perovskites contain lead halide compounds in their composition, such that wide-scale commercialisation may not be feasible due to environmental risks and the associated resource access limits. The alternative and more environmentally friendly inorganic metal halide perovskites however have a lower band gap and similarly low light absorption efficiencies compared to their organic counterparts, which negatively affects their performance. Current efforts aimed at achieving higher absorption efficiencies requires better understanding of their structural complexity, including quantitation of both light and heavy elemental impurities within the perovskite matrix. The concurrent use of Ion Beam Analysis (IBA) techniques such as Heavy Ion Particle Induced X-ray Emission (HI-PIXE) spectroscopy together with Time of Flight- Elastic Recoil Detection Analysis (ToF-ERDA) may be an effective method for studying these properties. For instance, PIXE can be used to provide information on the relative concentration of heavy elements, while ToF-ERDA can provide information on the relative concentration of light elements (from H up to O), along with elemental depth profiles of a material (as well as its thickness).

However, unlike with protons, using heavy ion probes like presents a challenge for PIXE due to the unavailability of X-ray production cross section data needed for atomic quantitation. This also extends to the analysis of heavy element targets such as Sn and Cs, which are typically found in metal halide perovskites like . Large discrepancies between theoretical predictions and experimental X-ray production cross section data exacerbate this limitation, requiring additional and substantial experimental measurements. This study therefore presents measurements of X-ray production cross sections of Sn and Cs induced by ⁶³Cu^q+ ion beams within the (20 – 34) MeV ion energy range.

The measurements were carried out using CsBr and thin films prepared using spin coating on Fluorine doped Tin Oxide (FTO) substrates. The cross section data is compared to conventional theoretical models such as the ECPSSR, developed from the binary encounter approximation, and is discussed in terms of the prominent ionisation mechanisms.

Speaker: Lilian Moremi (Tshwane University Of Technology)

103 Environmental radiometric assessment of uranium exploration test pits in Botswana: Implications for radiation monitoring, pollution risk assessment and ecological safety

Uranium exploration activities while essential for the advancement of resource development, present potential radiological hazards to adjacent ecosystems. The research examines the radiometric properties of test pits situated within the Letlhakane Uranium Project Lease Area in Botswana, with focus on the spatial variability in radiation exposure and its implications for ecological risk and radiation management practices. Using ground-based gamma-ray spectrometry, four test pits were assessed, comprising one open and three rehabilitated test pits. The findings showed notable spatial variability in absorbed dose rates, ranging from 34.3(2) to 1171.4(59) nGy/h, with an average of 388.6(19) nGy/h across the rehabilitated test pits, surpassing the global background radiation level of 59 nGy/h. The open test pit showed radiation levels approximating 800 nGy/h, which is an order of magnitude higher than the levels observed in surrounding undisturbed areas. The average Annual Effective Dose Equivalent for rehabilitated sites was calculated at 2.438(3) mSv/y in contrast to 0.466(2) mSv/y for adjacent undisturbed sites. The Excess Lifetime Cancer Risk were determined to be 0.0083(4) and 0.0017(1), respectively. These results underscore the potential for exploratory mining operations to substantially modify local radiation profiles and therefore raise concerns regarding the sufficiency of existing rehabilitation strategies and the need for early-stage radiological surveillance. By linking observed radiation levels to potential ecological and human health risks, the study provides a framework for proactive radiation assessment and management in uranium exploration contexts. The outcomes contribute to the scientific discourse regarding environmental impacts of mining operations and provide pragmatic insights for policymakers and industry stakeholders.

Keywords: radiation monitoring, ecological risk assessment, mining impacts, uranium exploration

Speaker: Mr Sankwasa Chika (BIUST)

104 Statistical Discrimination of Uranium Ore Concentrate Using Trace Element Signatures: Developing nuclear forensic fingerprints

Similar to ordinary forensics, nuclear forensic science uses data and modelling to infer historical information such as origin and production processes. To do this, unique characteristics of different nuclear material that make up nuclear fingerprint must be identified. To date, very few characteristics have been identified as signatures for uranium ore and uranium ore concentrate(UOC) including the REE pattern and trace elements (geological indicators of deposit type). In this study, the concentrations of trace elements: Ti, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Sn, Cs, Ba, W, Pb in 9 different UOC surrogate samples collected from Botswana and Nigeria were determined using Inductively Coupled Plasma Mass Spectrometry. The compositional trace element data were subjected to an arsenal of univariate and multivariate statistical analysis techniques such as correlation analysis, one-way Analysis of Variance, Principal Component Analysis, and Hierarchical Cluster analysis to quantify the statistical significance of the differences observed and to test the potential discriminative power of individual trace elements between ores from the same region. ANOVA revealed significant differences (p<0.5) in Ti, Zn and Pb only while no significant differences (p>0.05) were observed in V, Cr, Co, Ni, Cu, Ga, Rb, Sr, Y, Zr, Sn, Cs, Ba, W. The study further found three principal components that explained 91% of the variance in the UOC samples. PC1 (V, Ti, Pb, Sn), PC2 (Cr, Cu, Zr) and PC3 (Cs, Rb, Zn), respectively. This study highlighted the potential trace elements signatures to distinguish between uranium ore from different locations.

Speaker: Ms Liteboho Ntsohi (School of Physics, University of Witwatersrand, Johannesburg, South Africa)

105 Understanding the structure of $^{16}\text{C}$ and the $B(E2)$ problem through Large-Scale Shell-Model (LSSM) calculations

The structure of neutron-rich carbon isotopes continues to be a subject of interest in nuclear physics, particularly the nucleus $^{16}\text{C}$. One of the key unresolved issues is the variation in measured $B(E2)$ values for the transition from the first-excited $2_1^+$ state to the ground state, with reported values spanning nearly an order of magnitude. Traditional interpretations assume a simple model in which two valence neutrons couple to a $^{14}\text{C}$ core, requiring the introduction of a large effective charge to match experimental data. However, this approach does not fully capture the complexity of $^{16}\text{C}$’s nuclear structure.

This work presents results from a large-scale $(2 + 4)\hbar\omega$ no-core shell-model calculation of $^{16}\text{C}$, incorporating six major shells and employing the Zheng et al. interaction within the OXBASH framework. The analysis of the wave functions indicates significant mixing of higher-order configurations, challenging the validity of the simple two-neutron model. The theoretical predictions are further validated by comparing the computed excitation spectrum and intermediate-energy elastic proton scattering cross-sections with experimental data. Notably, the results demonstrate that a smaller, or even negligible, effective charge is sufficient to reproduce the accepted $B(E2)$ value, resolving discrepancies observed in previous studies.

Speaker: Khuliso Murulane (University of Johannesburg)

106 LEAD ISOTOPIC RATIOS AS A NUCLEAR FORENSIC SIGNATURE FOR AGE DATING OF URANIUM ORES

South Africa has four uranium “ore provinces”, and largely based
on the ages of the provinces, they have distinct nuclear forensics signatures. The International Atomic Energy Agency has mandated all its Member States to develop National Nuclear Forensics Libraries in response to the nuclear security threat posed by nuclear material trafficking. South Africa is thus enhancing their capabilities to interdict and attribute any nuclear material out of regulatory control within its borders, by undertaking this project to document the age and origin of uranium ore materials. In this project, we have determined lead (Pb) isotopic ratios of uranium ore sourced from South Africa and evaluated the Concordia Ages of the two uranium ores. Results show that Variations in the Pb isotopic ratios of different geologic deposits provides a unique nuclear forensic signature for dating the ores. Top ore had an age of 1.8 Ga while the deeper ore had an age of 3.8 Ga. This provides a new nuclear security tool for South Africa's nuclear materials.

Speaker: Manny Mathuthu (CENTER FOR APPLIED RADIATION SCIENCE AND TECHNOLOGY (CARST), NORTH-WEST UNIVERSITY (Mafikeng Campus))

107 Indirect experimental technique for constraining the 193,194Ir(n,γ) cross sections

The formation of elements, particularly those heavier than iron,
predominantly occurs through two neutron capture processes: slow
neutron capture process and rapid neutron capture process, each
contributing approximately 50%. These are known as the s- and
r-processes, respectively [1].
The neutron capture reactions 192Ir(n,γ)193Ir and 193Ir(n,γ)194Ir
were indirectly studied by analyzing data obtained from the Oslo
Cyclotron Laboratory (OCL). These data enabled the study of the
193,194Ir isotopes, originating from the 192Os(α,tγ) and 192Os(α,dγ)
reactions, respectively. The 193Ir(n,γ)194Ir cross sections constrained
by our measurements provided a comparison to existing (n,γ) mea-
surement data [2]. Additionally, the 192Ir(n,γ)193Ir reaction maps a
branching point in the s-process, making it highly significant. How-
ever, directly measuring the (n,γ) cross section is challenging due to
the instability of 192Ir. Therefore, the OCL data provided valuable
information on the 192Ir(n,γ)193Ir cross section by indirectly con-
straining it using the experimental nuclear level density (NLD) and
γ-strength function (γSF).
An array of Sodium Iodine (NaI)Tl detectors, called CACTUS,
detected γ-rays, while the silicon particle telescope array, called SiRi,
was used to detect charged particles in coincidence. The NLDs and
γSFs were extracted below the neutron separation energy, Sn, using
the Oslo Method [3]. Furthermore, the NLDs and γSFs were used as inputs in the open-source code TALYS to calculate the neutron cap-
ture cross-sections and Maxwellian averaged neutron capture cross
sections (MACS) for 193,194Ir. Final results of this study will be
presented in comparison to existing data.

[1] Arnould, M., Goriely, S., and Takahashi, K. (2007). Physics
Reports, 450(4-6), 97-213.
[2] Zerkin, V. V., and Pritychenko, B. (2018). The experimental
nuclear reaction data (EXFOR) 888, 31-43.
[3] Schiller, A., Bergholt, L., Guttormsen, M., Melby, E., Rekstad,
J., and Siem, S. (2000). Nuclear Instruments and Methods in Physics
Research Section A: Accelerators, Spectrometers, Detectors and As-
sociated Equipment, 447(3), 498-511.

This work is based on research supported in part by the National Re-
search Foundation of South Africa (Grant Number:PMDS22070734847),
SAINTS Prestigious Doctoral Scholarship, U.S. Department of Energy,
Office of Science, Office of Nuclear Physics under Contract No. DE-AC02-
05CH11231 and the SARChI under grant No REP-SARC180529336567. The experiment was financed through ERC-STG-2014 under Grant Agreement No. 637686

Speaker: Sebenzile Magagula (University of the Witwatersrand)

108 Radiological health risk assessment of powdered and liquid milk in South Africa: A study on activity concentration levels of 226Ra, 238U, 232Th, 40K and 137Cs

Our natural environment is endowed with natural radioisotopes to which humans are exposed through the ingestion of foodstuffs with consequent health implications. In this study, an assessment of the radioactivity levels in powdered and liquid milk available in South Africa was conducted to evaluate their associated radiological health risks. Both natural radioactivity sources such as 226Ra 238U, 232Th and 40K, as well as artificial radionuclides like 137Cs, were analyzed using gamma-ray spectroscopy. A total of twenty-eight frequently consumed milk samples were collected from the groceries stores in South Africa and measured using a high-purity Germanium detector. The results revealed varying levels of radioactivity in the milk products, with mean values of 29.940 ± 3.571 Bq/kg for 238U, 33.803 ± 4.655 Bq/kg for 226Ra, 29.508 ± 5.245 Bq/kg for 232Th and 573.553 ± 103.273 Bq/kg for 40K, for powdered milk. Liquid milk showed mean concentrations of 7.252 ± 1.215 Bq/L for 238U, 10.332 ± 0.731 Bq/L for 226Ra, 11.169 ± 1.137 Bq/L for 232Th and 137.072 ± 57.982 Bq/L for 40K. Artificial radionuclide 137Cs was not detected in the milk samples. The mean value of 40K for powdered milk exceeds guideline limit set by UNSCEAR for foodstuff. The mean annual effective dose was calculated to be 2.546×10-4 ± 0.189×10-4 mSv/y while the lifetime cancer risk was found to be 8.276×10-5 ± 6.170×10-5. The estimated mean values of radiological health risks of the milk samples are within the tolerable limit set by UNSCEAR and other global regulatory bodies. However, infants are at high risk by consuming up to 15 kg/year of powdered milk due to high radiation doses to vital organs of the range 1.659 ± 0.190 to 2.957 ± 0.339 mSv/y, but half the quantity is recommended. The findings of this study are comparable with those reported in the literature and provide valuable insights into the radioactivity levels in milk products in South Africa and their potential implications for human health. It shows that there is no significant radiological health impact due to the consumption of milk. However, continuous monitoring and further research on heavy metal contents are recommended to ensure the safety of milk consumption by the populace.

Speaker: Dr Samuel Odumu Ogana JOHN (Center for Applied Radiation Science and Technology (CARST), North-West University (Mahikeng Campus), South Africa.)

109 Portable African Neutron-Gamma Laboratory for Innovative Nuclear Science

iThemba LABS has pioneered a mobile gamma-ray detection unit[1] which allows a user to operate in the field and chart the location, strength and energy of gamma radiation.  The system incorporates a sensitive scintillation detector[2] typically used for accelerator-based spectroscopy at the SSC laboratory and was integrated into a backpack incorporating a fast 125 MHz digitiser for readout and a GPS enabled Raspberry Pi microprocessor system, allowing in situ measurements of radiation around the Cape Town site, with collected data streamed to the cloud and analysed offline. After conducting a series of rollout radiation measurement tests at Faure site, iThemba LABS has successfully used the gamma-ray detection system in collaboration with local and regional institutions to take radiation monitoring measurements from calibrated sources in the field, including radiation measurements tests conducted at Kruger National Park and at mining areas both in South Africa and in Botswana. It has also been used in the commissioning of the SAIF facility monitoring the performance of the water-cooling circuits.

The Portable African Neutron-Gamma Laboratory for Innovative Nuclear Science (PANGoLINS) project aims to investigate measurements of both gamma rays and neutrons which forms an important component part on site or in transit and the detection of both fissile material for the use in decarbonised energy sources or disposal thereof.  A core component of the project is be to miniaturize the weight of the gamma ray detection device and associated infrastructure so that it can be loaded on an unmanned aerial vehicle to enable access to, and enhance performance of radiation monitoring measurements at remote sites leading to autonomous operations.

PANGoLINS incorporates commercial detector assemblies of LaBr3(Ce), SrI2(Eu) and/or CLYC(Ce) for spectroscopy. In addition, the project encompasses the instrumentation of other scintillation detectors with silicon photomultiplier technologies. The coupling of these to readout devices such as high density ADC readout are planned for applications for nuclear science, medical imaging or astronomy.
An overview of the project, its progress and potential outcomes will be presented.

References
[1] Jones, P. et al., IEEE Nuclear Science Symposium (2023) doi: 10.1109/NSSMICRTSD49126.2023.10338129
[2] Msebi, L. et al., NIM-A. 1026 (2022) 166195, doi: 10.1016/j.nima.2021.166195

This work is based on the research supported wholly by National Research Foundation of South Africa (90741, 99037, 127116) and iThemba LABS.
** Supported 2023-24 by the Technology Innovation Agency under Grant number 14606/01
† Presenting author email: pm.jones@ilabs.nrf.ac.za
‡ Present address: Department of Chemistry, Tshwane University of Technology, Pretoria, South Africa.

Speaker: Pete Jones (iThemba LABS)

Nuclear, Particle and Radiation Physics-2

110 Triboson Excesses in light of a Real Higgs Triplet Model

In recent years, the ``multilepton anomalies'' have emerged, consisting of several persistent tensions in channels with multiple electrons and/or muons in the final states, with missing transverse energy and ($b$-) jets. These anomalies have prompted growing interest in the possibility of a new scalar particle beyond the Standard Model (SM).
In this context, excesses have been observed in the diphoton, $Z\gamma $ and $WW$ spectra, pointing toward the presence of a Higgs-like scalar $ S$ with mass $ m_S \approx 152 \pm 1 $ GeV.

While these excesses suggest the existence of a new resonance, the $ ZZ $ final state remains consistent with Standard Model predictions, showing no significant deviation. This consistency can be naturally explained if the scalar $ S $ belongs to a Real Higgs Triplet (RHT) with hypercharge $ Y = 0 $, which does not couple to a pair of $ Z $ bosons at tree level. In such a scenario, charged and neutral triplet scalars can be produced via Drell-Yan processes and decay into electroweak gauge bosons, leading to enhancements in triboson final states such as $WWW $, $ WWZ $, and $ WZZ $.

Recent ATLAS and CMS measurements of triboson processes report observed (expected) significances of $ 6.4\sigma ( 4.7\sigma $) in the $ VVZ $ channel and $ 4.4\sigma ( 3.6\sigma )$ in $ WWZ $. These can be interpreted as a possible link to the extended Higgs sector. In this study, we investigate whether the RHT Model with hypercharge $Y = 0$ can accommodate these triboson excesses through Drell-Yan production of triplet scalars, which subsequently decay into electroweak bosons, leading to an enhancement in triboson final states. We explore the parameter space where $S$ is identified as a component of the extended Higgs sector, with a small but nonzero diphoton branching ratio. Using Monte Carlo simulations, we analyze the predicted cross-sections for $WWZ$, $WZZ$, and $WWW$ production and compare them with current experimental data.

Speaker: Dr Srimoy Bhattacharya (School of Physics and Institute for Collider Particle Physics, University of the Witwatersrand)

111 Observation of 152 GeV charged scalar at future lepton colliders

The statistical significance of the "multi-lepton anomalies"—the discrepancies in the channels with multiple leptons, missing energy, and potentially ($b$)jets in the final states with the SM prediction—indicates the production of a scalar with a mass between 145 GeV and 155 GeV that is beyond the standard model. The associated production of a narrow scalar resonance of mass $\approx$ 152 GeV, with a significance of 5.4 $\sigma$ has been reported with the $\gamma \gamma$, $Z\gamma$, and WW final state. The requirement of the new scalar to decay dominantly to $WW$ final state by the anomalies and the absence of any excess in $ZZ$ final state significantly predicts the new scalar to be part of $Y=0$ scalar-triplet. The model contains a CP-even neutral Higgs ($\Delta^0$), and two charged Higgs bosons ($\Delta^\pm$), which are quasi-degenerate in mass. In this article, we focus on the possibility of finding the aforementioned predicted $\approx$ 152 GeV BSM charged scalar at the future proposed $e^+e^-$ collider. We emphasize on the pair production of the charged scalars, $e^+e^- \to \Delta^\pm \Delta^\mp$ and scrutinize various signal regions depending on the decay products of $\Delta^\pm$.

Speaker: Dr Siddharth Prasad Maharathy (School of Physics and Institute for Collider Particle Physics, University of the Witwatersrand)

112 Measuring the anomalous ttZ and ttγ couplings at Future e−p colliders.

We investigate the anomalous tt̅X couplings for neutral charged gauge boson X=Z/γ in the Standard Model (SM) and measure their precision beyond the SM in future electron-proton collider environments. The tt̅ quark pairs are produced in the neutral currents channel through the process e^- p → e^- t t̅ , for electron and proton beams of energy E_e = 60 GeV and E_p = 7 TeV respectively, at the center of mass energy of 1.3 TeV as proposed for the LHeC. The tt̅γ interaction is further probed through the photo-production process γp→t t̅ with γ scattered from the electron. We focus on the semileptonic channel where t → bW⁺, W⁺→l⁺ν_l and t̅→b̅W^-, W^-→l^-ν_l and investigate sensitive kinematic observables to these couplings. We observe that the azimuthal angular difference, ΔΦ, between the scattered electron and the l⁺ is the most sensitive observable to tt̅Z couplings. We further investigate sensitive kinematic observables to tt̅γ couplings in the photo-production process. We perform a χ² analysis at the inclusive and differential levels in the cross section to constrain the couplings.

Speaker: Dr Mukesh Kumar (University of the Witwatersrand)

Photonics: Biosensing & Diagnostics with Photonics

Convener: Christine Steenkamp (University of Stellenbosch)

113 Photonic-biosensing towards drug-resistant Tuberculosis diagnosis

Early detection and treatment of TB remain key strategies to reduce transmission and disease progression. However, this is hampered by time-consuming, insensitive diagnostic methods, particularly for the detection of drug-resistant forms and in patients with human immunodeficiency virus infection (HIV). Several genes, such as RNA polymerase β subunit (rpoB) and enoyl reductase (InhA) genes, contain mutations that are responsible for drug resistance. One objective of this study is to use a surface plasmon resonance (SPR)-based biosensor platform to detect rpoB and inhA genes. Deoxyribonucleic acid (DNA) probes, specific for rpoB and inhA, were used as biorecognition elements to capture rpoB and inhA target DNA. The rpoB and inhA gene-specific thiolated DNA probes were immobilized on a gold-coated glass substrate before the target DNA was introduced for detection. As a negative control, mis-matched DNA, unspecific to both genes were used for confirmation of binding of the target DNA in the SPR exper-imental setup. The SPR optical setup was used for the analysis of the binding interactions occurring on the coated glass substrate. The total reflected intensity indicated the kinetics associated with DNA hybridization occurring between the target DNA and the capture probe. This is the initial step towards potentially detecting drug-resistant mutations using SPR-based biosensors for a point-of-care setting.

Speaker: Ms Sipho Chauke (Council for scientific and Industrial research (CSIR) and University of Cape Town(UCT))

114 Laser-synthesized Selenium nanoparticles for SARS-CoV-2 detection using LSPR

Abstract: Accurate and timely diagnostics are essential for identifying infected individuals, enabling prompt treatment and control strategies to prevent further spread. The COVID-19 pandemic highlighted the critical role of diagnostic testing for disease preparedness and response. Conventional diagnostic techniques such as polymerase chain reaction (PCR) are effective at detecting viral pathogens, but they have shortcomings, such as long turnaround times. In this work,a photonic-based diagnostic tool, localized surface plasmon resonance (LSPR) integrated with selenium nanoparticles (SeNPs), is proposed. The laser ablation approach was used to synthesize SeNPs. Furthermore, an optical biosensing substrate coated with APTES was functionalized with SeNPs and Severe acute respiratory syndrome coronavirus 2 monoclonal antibodies (SARS-CoV-2 mAb). After characterization of the biosensing substrate, it was used for the detection of SARS-CoV-2 pseudovirus (analyte) using an in-house-built LSPR system. The presence of SARS-CoV-2 pseudovirus was successfully detected using LSPR integrated with SeNPs. In the presence of pseudovirus, a wavelength shift brought on by the SeNPs was observed, whereas the negative sample, which was pathogen-free, showed no shift. The LSPR technique can be translated into a rapid and accurate diagnostic tool for detecting infectious viral pathogens such as SARS-CoV-2, especially in point-of-care settings. Such photonics-based methods have the potential to contribute to addressing challenges with effective disease control and hence significantly reduce mortality rate due to the spread of infectious diseases.
Keywords: Selenium nanoparticles, SARS-CoV-2, Localized surface plasmon resonance, laser ablation

Speaker: Ms Zenande Mcotshana (National Laser Centre, Council for Scientific and Industrial Research, P.O. Box 395, Pretoria 0001, South Africa)

115 Dual Fabry-Perot Interferometric Fiber Sensors for Refractive Index Monitoring of Salt and Sugar Solutions Using Broadband Spectral Analysis

Abstract
The precise monitoring of chemical concentrations in liquids is critical for environmental, industrial, and biomedical applications. Optical fiber sensors, particularly those based on Fabry-Perot interferometry (FPI), offer high sensitivity, tolerance to harsh environments, and multi-sensing capabilities, making them ideal for detecting refractive index changes in various solutions. This study presents the design and implementation of an FPI sensor for real-time monitoring of refractive index changes in salty and sugary aqueous solutions. The sensor comprises two distinct open-cavity Fabry-Perot sensor heads, each tailored to a specific solution. The cavities are fabricated by chemically etching the tip of a single-mode optical fiber using Hydrofluoric acid (HF) and then splicing it with a cleaved single-mode fiber to form air-gap microcavities. The two sensor heads differ in cavity length, allowing them to produce unique interference patterns within a combined reflected spectrum. A broadband light source is directed into the system via a circulator and a 50/50 coupler, enabling simultaneous interrogation of both sensors. The reflected signals from each sensor are recombined and analyzed using an optical spectrum analyzer (OSA). As the concentrations of salt and sugar are gradually increased, corresponding shifts in the interference fringes are observed due to changes in the refractive indices of the solutions. The difference in cavity lengths enables spectral separation of the two sensor signals. A Fast Fourier Transform (FFT) is applied to the combined spectrum to isolate each sensor’s contribution based on their distinct spatial frequency responses. The change in the refractive index of the solution can be estimated using the Free Spectral Range (FSR - distance between two adjacent peaks). The proposed FPI sensor system successfully demonstrates the ability to simultaneously monitor and distinguish refractive index changes in two different liquid solutions using a compact and cost-effective optical setup. The technique shows strong potential for multi-parameter sensing applications in chemical, biomedical, and environmental monitoring.

Keywords: Fabry-Perot Interferometer, Concentration, Fast Fourier Transform, Free Spectral Range

Speaker: Sandisiwe Bangani (Nelson Mandela University)

Physics for Development, Education and Outreach

116 Assessment of Undergraduate Physics Students’ Misconception about Heat and Temperature and Implications for Instruction

Heat and temperature are fundamental concepts introduced in undergraduate physics thermodynamics with application in mechanics, energy, technology as well as in allied scientific disciplines such as materials science and chemistry. Towards promoting greater understanding of these concepts among students, it is important to identify student misconceptions. In this study, undergraduate physics students’ conception of heat and temperature were assessed using the Heat and Temperature Concept Evaluation (HTCE) test instrument developed by Thornton and Sokoloff. The study covered 8 conceptual areas as follows: heat and temperature, rate of cooling, calorimetry, rate of heat transfer, perception of hotness, specific heat capacity, change of phase and thermal conductivity. Study results revealed student difficulties in the conceptual areas of heat and temperature, rate of cooling, rate of heat transfer and specific heat capacity. Interventions to improve student understanding to include experimentation are discussed.

Speaker: Enock Jonathan

117 Strengthening First-Year Physical Sciences Success: A Five-Year Analysis of Throughput with an Emphasis on AI-Driven Strategies

In recent years, declining student success rates, particularly in first-year programs, have become a critical concern in higher education. This study examines throughput rates in first-year physics and chemistry courses over a five-year period, drawing on data from an extended curriculum program to identify and address key challenges. At the core of this study is the integration of Artificial Intelligence (AI) to enhance teaching and learning processes. Grounded in the Technological Pedagogical Content Knowledge (TPACK) framework, the study explores how AI can be embedded into the physical sciences curriculum to support student engagement and content mastery without disrupting existing pedagogical methods. By leveraging AI, the study aims to bridge the gap between theoretical knowledge and practical application, thereby improving throughput rates. Findings indicate that AI-driven strategies have significant potential to enhance student success in first-year physical sciences programs. AI-powered tools can facilitate personalized and adaptive learning experiences, leading to improved student engagement and retention. However, continuous assessment and refinement of these strategies are essential to ensure their effectiveness in meeting the evolving needs of students. By fostering AI-enhanced learning environments, institutions can reduce dropout rates, alleviate the demand on student support services, and implement more targeted interventions for at-risk students.

Speaker: Sewela Khunoana

118 Practical teaching methods for enhanced interest in teaching and learning Physics for undergraduate university students

Challenges in the teaching and learning of physics existed as far as education existed worldwide. Lecturers and facilitators continually seek various approaches that could yield desirable results. However, the learning gains have mostly been disappointing, and physics is labelled as a difficult subject for the chosen few. That idea encouraged instructors to accept physics failure rates as normal. Whilst other efforts and approaches, which include extra classes and winter schools, are continually used, departing from the belief that physics is for the chosen has proven to be a challenge. In this work, we explore how teaching and learning can be enhanced using some ‘easy-to-adopt approaches’ that can potentially give desired results. The concept identification of prior learning of learners’ understanding of the concepts, how to use social constructivism teaching strategies, and evaluating the effectiveness of these teaching and learning strategies will be presented.

Speaker: Prof. Buyisiwe Sondezi (Department of Physics, University of Johannesburg, Cnr Kingsway Avenue and University Road, Auckland Park, 2006, South Africa)

Physics for Development, Education and Outreach

Convener: Mark Herbert (University of the Western Cape)

Physics of Condensed Matter and Materials

Physics of Condensed Matter and Materials 2

Theoretical and Computational Physics: Session 5

Convener: William Horowitz (University of Cape Town)

119 Eigenvalue determination for a Toy and Woods-Saxon Potentials using unsupervised PINN

Traditional numerical methods have been widely used to determine eigenvalues in quantum few-body problems. But little effort has gone towards exploring novel approaches like Physics-Informed Neural Networks (PINNs) as an alternative. In this work we shall explore the application of PINNs to determine the low-lying bound state for a toy molecular potential and the Woods-Saxon potential. The former is mainly used as a test bed for testing the accuracy of new theoretical models. The latter is a more realistic potential used to model the inter-action between nucleons inside the nucleus. Utilizing the unsupervised PINN framework to determine the eigenvalues for the radial Schrödinger equation, this framework approximates the eigenfunction by a trial solution that automatically satisfies the bound state boundary conditions. Preliminary results demonstrate that the PINN model has the potential to
predict the bound states’ eigenvalues for the molecular potential, thus indicating the viability of PINNs as a powerful alternative for solving eigenvalue problems in quantum-few body problems.

Speaker: Tshegofatso Tshipi

120 Laplacian eigenmodes in twisted periodic topologies for new physics models

Laplacian eigenmodes in non-trivial topologies (e.g. having twisted periodicity) are important in constructing a complete picture of the physics at play within models that incorporate compact extradimensional spaces. Determining them analytically is generally unwieldy, and the existing standard numerical methods have limited ability as spatial dimensions increase and when computing higher-index eigenmodes is required. To determine the feasibility of using physics-informed neural networks to compute Laplacian eigenmodes, we apply them to three primitive test cases: the Möbius strip, the real projective plane ($\mathbb{R} P^2$) and the 3-torus ($T^3$) in Cartesian coordinates. The neural networks approach's potential performance beyond solving the simpler cases is estimated in terms of the approximation errors obtained by comparing with known analytical solutions.

Speaker: Anele Ncube (University of Johannesburg)

121 Reservoir Computing for Predicting Chaotic Dynamical Systems

Time series prediction is the process of forecasting future values of a system by analysing historical data to identify patterns, trends and variations. There are two main approaches to time series prediction: model-based and data-driven. Chaotic dynamical systems are often difficult to predict due to sensitive dependence on initial conditions leading to possible long-term divergence in trajectories. Data-driven models make use of machine learning methods for training. Reservoir computing, a type of recurrent neural network, makes use of an existing dynamical system as a reservoir to train the neural network instead of having numerous hidden layers. “Classical” machine learning models often require extensive data and computational resources for training, while reservoir computing achieves comparable results with less. Due to its design, reservoir computing excels in the prediction of chaotic time series arising from unknown dynamical systems. In order to demonstrate the predictive ability of reservoir computing, a reservoir computing model was trained on samples of time series from the Sine, Logistic and Hénon maps. The reservoir computing model was then used to predict both the time series and essential dynamics of the three dynamical systems. The reservoir computing model was only capable of performing short to medium term time series predictions. However the model was also capable of learning dynamical properties not found in the training data such as a systems fixed points, attractor, and Lyapunov exponents. The results demonstrate that reservoir computing can be used to successfully predict and analyse various chaotic dynamical systems.

Speaker: Mr Taheer Jooma Abbajee (Department of Mathematics and Applied Mathematics, University of Johannesburg, Johannesburg, Gauteng, South Africa)

10:20 AM Morning Tea

Applied Physics

Convener: Lucas Erasmus (UFS)

122 IoT-Based Environmental Monitoring in a Sawtooth Greenhouse: Foundations for CFD, Anomaly Detection, and Environmental Prediction

The global agriculture sector faces mounting challenges due to climate change, rising atmospheric CO₂ levels, and increasing food demand from growing urban populations. Greenhouses have emerged as vital solutions to ensure improved food production. In earlier work, a real-time Internet of Things (IoT) sensor network was deployed in a sawtooth-shaped greenhouse to monitor temperature and humidity distributions. This provided key insights into the microclimate and laid the groundwork for future integration with computational fluid dynamics (CFD) simulations, aimed at optimizing natural ventilation, energy use, and environmental control.

Expanding on that framework, this study implements an enhanced IoT-based sensing network in a greenhouse, monitoring temperature, humidity, CO₂ equivalence (CO₂eq), and total volatile organic compounds (tVOC) across nine spatially distributed locations grouped into three zones (high-irradiation vent, middle, and far end). Over a 50-day period, a statistical filtering algorithm was used to remove sensor noise and quantify uncertainty, ensuring high data integrity from these locations. Results showed elevated temperatures and poor air quality (high CO₂eq and tVOC) at the high solar radiation vent, while the middle and far-end zones exhibited more favorable conditions due to high ventilation.

This dataset offers a valuable foundation for future CFD studies by providing detailed spatial and temporal environmental insights essential for model validation and simulation benchmarking. This is the basis for a digital twin that can be used to optimise crop yield growth and updated by real-time sensor data. Additionally, the high-resolution data and established patterns open new avenues for anomaly detection and predictive modeling of environmental conditions within greenhouses. These capabilities are critical for developing intelligent climate control strategies and advancing precision agriculture technologies for an increase in crop production.

Speaker: Abdool Sattar Cassim (University of Johannesburg)

123 Simulation and Image Reconstruction for a Low-Cost PET Detector Concept

A simulation of a low-cost PET detector concept is presented. The model is used to evaluate the imaging potential of the proposed detector, to optimise image reconstruction techniques for this design, and to feed back performance metrics to the detector design process.

The PET system was developed with GATE (Geant4 Application for Tomographic Emission), incorporating a detector layout based on modular scintillators and SiPM arrays. Simulation-based and analytic models of module and channel occupancies are used to assess the feasibility of signal multiplexing to reduce data acquisition electronic costs.

Reconstruction of simulated data is performed using both Filtered Back Projection (FBP) and Maximum Likelihood Expectation Maximisation (MLEM). The performance of these classical algorithms is compared for the low-cost detector concept, with and without integration of time-of-flight (TOF) and depth-of-interaction (DOI) information. Due to the reduced system size and sparse detector layout, TOF and DOI have limited impact, and this comparative study aims to demonstrate that high-quality, clinically usable images can still be obtained despite these constraints.

Benchmark studies using realistic brain phantoms are used to compare image quality from the low-cost system with that of a standard full-ring commercial PET scanner. These studies aim to establish the viability of simplified PET detector designs in producing clinically relevant imaging, contributing to more accessible diagnostic tools in low-resource settings.

Speaker: Ms Jemma Bagg (University of Cape Town)

124 Design considerations for a low-cost PET brain scanner

Medical PET is an expensive metabolic imaging technique that has applications in cardiology, oncology and neurology and is primarily limited to high income countries. A low-cost PET detector concept would likely extend its application to middle and low income countries. This work aims to find the optimal physical parameters that minimizes the cost of the detector while still producing clinically relevant images. The detection method used by the proposed detector is a combination of pixelated scintillation material and silicon photomultipliers. The performance of said detector is described by how many of the produced photon pairs are captured (sensitivity) and how accurately it measures the photon pairs traveled path (spatial resolution). The primary factors that affect the cost are the total amount and type of scintillation material, the number and type of silicon photomultipliers and the number of electronic readout channels. The means of cost reduction for the traditional PET ring design that will be explored are reducing the ring diameter to restrict its function to brain PET, manufacturing custom SiPM arrays, reducing the total number of electronic readout channels with multiplexing schemes and utilizing larger cheaper SiPMs, strictly FPGA based DAQ hardware, sparser SiPM arrays and cheaper scintillation material. The performance reductions introduced by these design choices are to be overcome by using finer grained pixels to increase spatial resolution, integrating the scanner into a low-field MRI and using single-sided readout depth-of-interaction to reduce parallax error and maintain low-cost. Beyond the traditional detector design, novel mechanical detector designs are explored. Mathematical modeling is used to understand how the alterations in physical parameters affect cost and performance and how the proposed performance enhancing methods may combat the reduced performance. Preliminary designs for a low-cost PET detector concept that are ready for integration into a low-field MRI are presented.

Speaker: Simon Carthew (University of Cape Town)

125 Gone with the Wind...or Not? Tracking Light's Twists

Optical vortices—phase and polarization singularities—are central to structured light applications, yet their comparative resilience to atmospheric turbulence remains underexplored. This study investigates the robustness of phase versus polarization vortices under Kolmogorov-model turbulence using Laguerre-Gaussian and vector beam superpositions. Vortex dynamics are tracked via phase unwrapping and Stokes parameter analysis to quantify spatial drift and topological stability. Understanding the resilience of phase and polarization vortices to atmospheric turbulence can enhance the reliability of structured light in applications such as free-space optical communication, remote sensing, and optical trapping.

Speaker: Vasili Cocotos (University of the Witwatersrand)

126 Warping light into Neural Networks

In recent years, Deep Diffractive Neural Networks (D2NNs) have emerged as a powerful tool in optical computing and information processing. These systems utilise consecutive phase modulations to map a set of optical input states defined in one basis, to a new set of target states in an arbitrarily defined basis. Traditionally, the phase masks used to achieve these operations are optimised through randomly generated phase patterns or by finetuning individual pixel values using various search algorithms. In this work, we introduce a novel approach to the construction of these phase screens using Zernike polynomials. Switching from the pixel basis to this modal basis allows us to train the coefficients of the polynomials contained in each phase screen analogously to the weightings found within a traditional neural network - fewer training parameters lead to reduced computing cost and results in faster convergence during training. We demonstrate the computational abilities of this approach by characterising Laguerre Gaussian modes into predefined channels, as well as by emulating a quantum gate operation using vectors defined as a lattice of Gaussian modes. This work advances high-dimensional free-space information processing and has the potential to be adapted to real-time processing tasks.

Speaker: Mr Hadrian Bezuidenhout (University of the Witwatersrand)

Astrophysics & Space Science: Space Science Session 3

Convener: Ruhann Steyn (Centre for Space Research, North-West University)

127 Modelling Earth’s magnetic field over the South Atlantic Anomaly region using Swarm satellite and ground-based data

The Earth’s magnetic field plays a critical role in shielding our planet from solar and cosmic radiation,
yet the South Atlantic Anomaly (SAA) region represents a significant weakening of this
protective shield. This research aims to model the temporal and spatial evolution of the SAA
region using the Revised Spherical Cap Harmonic Analysis (R-SCHA) technique, providing improved
regional characterization and predictive capabilities. Utilizing satellite data from Swarm,
alongside ground-based observatory records, we aim to refine regional predictions of the SAA’s
extent and intensity. The R-SCHA technique offers an enhanced resolution of localized magnetic
variations, crucial for understanding the anomaly’s underlying geodynamo processes and space
weather impacts. Preliminary results will be presented, showcasing advanced data selection and
processing techniques, which are essential in core field modelling as external field contributions
must be minimized. Additionally, an analysis of all ground-based magnetic station records within
the SAA region will be discussed, to further improve modelling accuracy. These findings are evaluated
through a comparative analysis with the CHAOS-7 global magnetic field model to assess
their accuracy and reliability.

Speaker: Sanele Lionel Khanyile (South African National Space Agency)

128 Statistical Interpretation of the Thermospheric Density Responding to Geomagnetic Disturbances

Variations in thermospheric density play an essential role in satellite operations, particularly during
geomagnetic disturbances, where fluctuations in atmospheric drag impact orbital stability. A
significant incident on February 4, 2022, saw SpaceX lose 38 Starlink satellites due to unanticipated
atmospheric drag following a geomagnetic storm. This study aims to identify high- risk periods in
thermospheric density using observational data from ESA’s Swarm Satellite C. By integrating key
geomagnetic indices such as Kp, AE, and SYM-H, this research studies the geomagnetic activity
with thermospheric density variations to assess space weather disturbances. The study uses statistical
analysis to develop a predictive framework for identifying potentially hazardous periods,
ensuring future satellite missions are better equipped to prevent similar risks. Data visualisation
techniques, including plotted density fluctuations, provide deeper insights into the relationship
between geomagnetic activity and atmospheric variability. The findings contribute to a broader
understanding of thermospheric dynamics and their implications for satellite operations, mission
planning, and the long-term sustainability of space activities.

Speaker: Ms Sthandiwe Msomi (University of KwaZulu-Natal)

129 Modelling and observation results for the 23-25 March 2023 geomagnetic storm

This talk will present results of ionospheric changes during the 23-25 March 2023 geomagnetic
storm using observational and modeling data over the African-European sector. Both ionosonde
and Swarm observational results show that mid latitudes experienced negative storm effects which
have been attributed to thermospheric composition changes. We use models to simulate the ionospheric
behavior during this storm period. Considered models were Thermosphere Ionosphere
Electrodynamics General Circulation Model (TIE-GCM) and the three-dimensional storm time empirical
model (3D-NNstorm) constructed based on radio occultation and ionosonde data. For the
maximum electron density of the F2 layer, TIE-GCM and 3D-NNstorm models provide correlation
values ranging between 0.48-0.64 and 0.64-0.88, respectively, with lower performance observed at
low latitudes.

Speaker: John Bosco Habarulema (South African National Space Agency)

130 The impact of geomagnetic storms and solar proton events in May and October 2024 on South Africa’s upper atmosphere, compared to the historical event of October 2003

This study investigated the impact of solar proton events (SPE) on the upper atmosphere over
South Africa during intense geomagnetic storms in May (Dst = -412 nT) and October 2024 (Dst
= -333 nT). Utilizing the NRLMSISE-2.0 atmospheric model and SOHO data, we characterized
storm-time atmospheric composition and energetic particle fluxes. Significant fluctuations in atmospheric
constituents were observed, with molecular nitrogen (N₂) increasing by
3.61×10⁶ cm^-3 day^-1 during the May sudden storm commencement
(SSC) and by 1.40×10⁶ cm^-3 day^-1 and 2.26×10⁶
cm^-3 day^-1 during the two-step SSC of October. A decrease in atomic
hydrogen (H) of about 3.0×10⁴ cm^-3 day^-1 occurred in
May, while the largest decrease of approximately 8.60×10³ cm^-3 day^-
1 was noted during the October storm. These changes, driven by particle precipitation that
enhances nuclear and molecular interactions at GNSS altitudes (400 –450 km), affect the total electron
content (TEC) and may compromise GNSS signal accuracy. The results are compared with
the historical event of solar cycle 23 in October 2003 (Dst = -353nT). This research enhances our
understanding of space weather’s impact on the upper atmosphere and related technologies.

Speaker: Joseph Omojola (North-West University)

131 Characteristics of Nighttime Medium-scale Traveling Ionospheric Disturbances: Longitudinal Comparison of their Seasonal and Local Time Variations

This study presents a statistical analysis of the occurrence rate of midlatitude nighttime medium
scale traveling ionospheric disturbances (MSTIDs) that were detected in Swarm plasma density
measurements from 2014 to 2023. Monthly and local time variations of MSTID occurrence rates
are compared in four longitude sectors: America, Africa, Asia, and Pacific. The spatial distribution
showed a longitudinal variation as the MSTIDs were abundant in the Pacific region and scarce in
the African sector. While the MSTIDs had occurrence peaks during both solstices, the winter solstice
peak dominated in all longitude sectors, representing a seasonal asymmetry. The local time
variation of the MSTIDs revealed they occur predominantly during the postmidnight hours in all
longitude sectors. However, post-sunset MSTIDs observations were enhanced over the Asian and
Pacific sectors during the solstices. The longitudinal variation in the occurrence of MSTIDs is probably
linked to the E–F coupling as it matched that of the nighttime sporadic E variation obtained
from ionosonde measurements. While the semiannual seasonal variation may be explained by
interhemispheric E–F coupling, the winter dominance of MSTIDs matches that of gravity wave activity.
This indicates that gravity waves probably play a major role in seeding the MSTIDs observed
in this study. Theoretical assessments of the longitudinal variations of MSTID driving mechanisms
are needed to better understand the seasonal asymmetry and how it is affected by solar activity.

Speaker: Zama Katamzi-Joseph

Nuclear, Particle and Radiation Physics-1

Nuclear, Particle and Radiation Physics-2

132 Searches for scalar resonances with di-photon in association with taus using the easyjet analysis framework in ATLAS detector at the LHC

Recent studies (arXiv:2109.02650, 2306.17209, 2503.16245) have identified growing excesses in scalar resonances with di-photon at the Large Hadron Collider (LHC), suggesting the presence of scalar particles beyond the Standard Model. These scalar resonances are motivated by the multi-lepton anomalies at the LHC which indicate a potential new scalar particle $S$ with a mass of approximately $151.5~\mathrm{GeV}$, originating from a heavier scalar $H$ with a mass near $270~\mathrm{GeV}$, with a global significance of $\sim 5\sigma$. Motivated by these findings, the HBSM group within the HMBS physics group at ATLAS has launched a new analysis using the easyjet analysis framework. This analysis focuses on searching for scalar resonances through di-photon production in the process $g g \to H \to S S'$, where $S \to \gamma\gamma$ and $S'$ decays to $S' \to \tau_h \tau_\ell$. We are preparing to use the analysis tools to analyse the 2022-2024 Run~3 data with an integrated luminosity of $183~\mathrm{fb}^{-1}$ at $\sqrt{s} = 13.6~\mathrm{TeV}$

Speaker: Mr Kutlwano Makgetha (University of the Witwatersrand)

133 Monte Carlo generation involving searches for scalar resonances with diphoton in association with tau+ tau-/2 b-jets in ATLAS detector at the LHC

A Monte Carlo generation campaign has been submitted under the HBSM subgroup to study a simplified model featuring the resonant production of scalar particles at the electroweak scale. The process under consideration is $ gg \rightarrow H \rightarrow SS' $, where the scalar $ S $ (with a mass of approximately 150 GeV) decays to a diphoton final state $( \gamma\gamma )$, and the accompanying scalar $ S' $ (with a mass of approximately 95 GeV) decays to either $ b\bar{b} $ or $ \tau^+\tau^-$. The motivation for these studies is rooted in the persistent multi-lepton anomalies observed in various channels at the LHC, as highlighted in combined searches for scalar resonances by ATLAS and CMS and further explored in the context of electroweak-scale scalar states decaying to photons, leptons, or $b$-jets [arXiv:2109.02650, arXiv:2306.17209, arXiv:2503.16245].The MC production is designed for Run 3 conditions at a center-of-mass energy of $ \sqrt{s} = 13.6$ TeV and will facilitate detailed kinematic studies and optimization of selection strategies in these channels.

Speaker: Njokweni Mbuyiswa (University of the Witwatersrand)

134 Searches for a scalar resonance with Di-photon in association with leptons in the range 130 – 200 GeV in the ATLAS detector at the LHC

Searches for di-photon resonances at the ATLAS experiment have primarily focused on the mass range of $200$–$3000\,\mathrm{GeV}$. However, phenomenological studies based on Run 1 data have reported excesses-commonly referred to as multi-lepton anomalies-suggesting the possible existence of a scalar resonance with a mass of $150 \pm 5\,\mathrm{GeV}$. Further investigations of $\gamma\gamma$ and $Z\gamma$ sidebands, using ATLAS and CMS data, have further motivated the presence of a narrow resonance in this region, with a reported local significance of $5.4\sigma$. The analysis aims to highlight this gap by proposing further investigation into this phase space, which is deliberately chosen to avoid overlap with the Standard Model (SM) Higgs boson. Two theoretical models are explored: the Two-Higgs-Doublet Model with an additional singlet (2HDM+S), and the Triplet Model ($\Delta$SM) with hypercharge $Y=0$. Both frameworks predict rich di-photon phenomenology in association with final states containing tau jets ($\tau$), leptons ($\ell = e/\mu$), b-jets, jets, and missing transverse energy (MET). Significant progress has been made within the 2HDM+S framework, particularly in key channels such as $gg \to H(250\,\mathrm{GeV}) \to S(\gamma\gamma)\, S'(\tau\tau/b\bar{b}/\ell+b/\ell\ell)$. Future work will extend the analysis to the $\Delta$SM model to fully explore this promising region of parameter space.

Speaker: Vuyolwethu Happyboy Kakancu (University of the Witwatersrand)

135 Event Selection and Analysis Strategy for Diphoton Resonance Searches Accompanied by Leptonic Final States in 2022-2024 ATLAS Run 3 data

The search for new scalar resonances at the Large Hadron Collider (LHC) is motivated by beyond the Standard Model (BSM) scenarios such as the Two-Higgs-Doublet Model with an additional scalar singlet (2HDM+S) and the Real Higgs Triplet Model. The 2HDM+S and Triplet model BSM frameworks is being used to study new scalar particles that may decay into final states involving photons and leptons. In particular, these models motivate searches for di-photon signatures accompanied by leptons. This study focuses on scalar resonance production via the process $gg \rightarrow H \rightarrow SS'$, where $S \rightarrow \gamma\gamma$, and $S'$ decays into one or more leptons and/or hadrons. Relevant decay modes of $S'$ include $\tau$, $\ell + b$ ($\ell = e, \mu$), and multi-body final states such as $2\ell$, $2\tau$, or combinations thereof. Among the various final states, particular attention is given to the channels $\gamma\gamma + \ell$ and $\gamma\gamma + 2\ell/2\tau$, given their sensitivity to scalar resonances and experimental accessibility. We are currently developing analysis strategies and selection tools in preparation for the analysis of Run~3 data, corresponding to an integrated luminosity of $183~\mathrm{fb}^{-1}$ at $\sqrt{s} = 13.6~\mathrm{TeV}$. The goal is to identify signal-like events while mitigating dominant SM backgrounds.

Keywords: $\gamma\gamma + \ell$,$\gamma\gamma + 2\ell$

Speaker: Kgothatso Ntumbe (Universitty of the Witwatersrand(ZA))

136 A Search for a Scalar Resonance using Di-Photons in Association with a lepton and a b-jet with the ATLAS Detector

The Multi-lepton anomalies at the LHC are indicative of a scalar resonance with a mass around $150 \pm 5$\,GeV in the $\gamma \gamma$ and $Z \gamma$ spectra in association with leptons and jets with a global significance of $5.4 \sigma$. This provides a compelling avenue for exploring new physics beyond the Standard Model using the di-photon channel. This project investigates the hypothesized resonance, where the scalar decays into a photon pair accompanied by a muon or electron and a $b$-jet $S(\rightarrow \gamma \gamma) + \geq 1 \ell +b$-jet. An analysis of the ATLAS data will be done in this channel, using the easyjet analysis framework, thus possibly reinforcing the hypothesis.

Speaker: Baballo-Victor Ndhlovu (University of the Witwatersrand)

Photonics: Laser Characterisation & Spectroscopy

Convener: Prof. Tjaart Krüger (University of Pretoria)

137 Group delay dispersion measurements using the i2PIE pulse characterization technique

Group delay dispersion (GDD) plays an important role in the creation and control of ultrashort pulses. As ultrashort pulses travel through dispersive media, the different frequency components travel at different speeds, increasing the pulse duration due to broadening of the pulse temporal profile. To create transform limited pulses (pulses that are as short as allowed by the available bandwidth), there needs to be a flat phase profile across all the frequencies that are present in the pulse. It is therefore important to be able to characterize optical materials used in nonlinear optics experiments, since these materials influence the pulse length of ultrashort pulses and the outcome of the experiments.

We demonstrate the use of the i$^2$PIE pulse characterization technique to measure the GDD of various optical materials (e.g. quartz window, microscope slide). i$^2$PIE is used to measure the amplitude and phase of the pulse. The GDD is found by fitting a parabola to the measured phase profile of the broadband laser pulse after passing through the sample. The GDD of the samples can be determined with a resolution of ±5 fs$^{2}$, which is comparable with standard GDD measurements, and an order of magnitude better than GDD measurements using the MIIPS pulse characterization scheme. This highlights the versatility of the i$^2$PIE pulse measurement protocol and its superior performance when compared to other existing pulse characterization techniques.

Speaker: Eugene Fouche (Stellenbosch University)

138 Voltage-Based Wavelength Tuning of a DFB Laser Using an Enhanced LM331 Frequency-to-Voltage Converter for OPLL Applications

This research demonstrates voltage-based control of a Distributed Feedback (DFB) laser, forming a foundational step toward the implementation of an Optical Phase-Locked Loop (OPLL). The voltage control mechanism is realized through a Frequency-to-Voltage Converter (FVC) using the LM331, which converts an offset frequency - generated by frequency mixing of a signal generator and a stable crystal oscillator - into a corresponding DC voltage signal. This voltage is then fed directly into the DFB laser, effectively tuning its emission wavelength. The tuning behavior is monitored using an Optical Spectrum Analyzer (OSA), providing real-time feedback on the laser’s spectral response. A key challenge addressed in this work is the inherent 100 kHz upper limit of the LM331-based FVC. By carefully modifying the circuit design, the conversion range is extended to accommodate frequencies up to 3 MHz.The experimental results show a clear voltage response starting from 40 kHz, reaching approximately 4.6 V at 3 MHz, and remaining at 0 V at 0 kHz—demonstrating a consistent and usable voltage-frequency relationship. This extended range enables more flexible and precise laser control, which is essential for the operation of OPLLs. Such systems require accurate phase locking between optical sources, a capability critical in high-speed optical communication, coherent detection schemes, and technologies like Radio over Fiber for 5G and beyond. By successfully enhancing the FVC’s range and demonstrating practical wavelength tuning of the DFB laser, this work contributes a crucial building block toward scalable and stable OPLL systems.

Speaker: Lilian Mutia (Nelson Mandela University)

139 Ag-H2O nanofluids by pulsed laser liquid-solid interaction for heat removal in electronics devices

We present Pulsed Laser Ablation in Liquid Solution (PLAL), a one-step pulsed laser ablation technique that produces a stable Ag-H2O nanofluid with improved thermal conductivity. Throughout the synthesis procedure, several deposition durations and fluences of the Nd YAG. Spherical nanoparticles (21–37 nm) having instability at higher concentrations are revealed by characterization. At 45°C (ta = 5 min), the thermal conductivity improvement is readily visible and reaches a maximum within 14–20%. In terms of the contact angle, laminar flow at the Cu interface is most likely indicated by ∆Ө<95 Deg. The impact of fluid flow is highlighted by concentration-dependent effects on the contact angle. Tube surface design emphasises design considerations via influencing flow.

Speaker: Mr Snenkosi Dlamini (UNIZULU)

140 Synthesis and characterization of Cerium III ion doped zinc selenide thin films prepared by chemical bath technique for luminescence application

ZnSe:x% Ce³⁺ (x = 0, 2, 4, 6, 8 and 10) thin films were deposited using chemical bath technique. All the films samples revealed wurtzite phase ascribed to ZnSe and the presence of the Ce³⁺ did not change the films structure apart from the shift in peak position to longer wavelength when compared to the undoped sample. The red shift is due to the incorporation of the dopant ions into the host matrix. Raman spectroscopy revealed two optical phonon peaks due to first and second order longitudinal modes. The films samples showed flakes-like morphological while the presence of the anticipated elements was confirmed by energy dispersive X-ray spectroscopy. The cross sectional SEM morphology has shown increase in the thin films thickness with increased Ce³⁺ ion concentration. FTIR revealed O-H stretching vibration modes as well as inorganic bands attributed to ZnSe. Atomic force microscopy showed a decrease in surface roughness with increased Ce³⁺ concentration although with fluctuation. The ultraviolet-visible spectroscopy results showed increased band gap energy with an increase in Ce3+ concentration and the values were dependent on the crystallite size. The undoped sample showed three luminescence peaks, which are due to the band-to-band and defects within the host material. Although there was no evidence of emission from the Ce³⁺ ions, increasing the Ce³⁺ doping concentration resulted in enhancement of the emission peak intensities. The enhanced emission luminescence due to Ce³⁺ ion doping, wide band gap, the stable structure and morphology make the deposited thin films good candidates for optical applications especially in LEDs.

Speaker: Dr Donald Dehiin Hile (University of Zululand)

141 Optical Quadrature Microscopy with a polarization-sensitive camera

Quantitative Phase Imaging (QPI) is an imaging technique enabling non-invasive, label-free measurement of optical path length differences within samples, facilitating three-dimensional reconstruction from two-dimensional microscopy data. This is traditionally achieved using interferometric approaches such as Phase Shifting Interferometry (PSI) where interferograms generated by combining reference and object beams with controlled phase shifts, are measured.

In this study we explore Optical Quadrature Microscopy (OQM), a variation of PSI that utilizes a quarter-wave plate combined with a rotatable analyzer to introduce controlled phase shifts in the reference arm of a Mach-Zehnder interferometer. We eliminate the need for an analyzer by integrating a polarization sensitive camera, potentially quadrupling the acquisition rate and enhancing temporal resolution. The details of the optical setup as well as preliminary results which validate the system's capability to perform accurate quantitative phase measurements will be presented. Additionally, the implications of our approach for studying dynamic samples will be discussed.

Speaker: Calvin Groenewald (Stellenbosch University)

Physics for Development, Education and Outreach

142 Quantum computing education availability in South Africa

Several formal initiatives, universities, and research institutions are working on quantum computing education in South Africa. This study explores the availability of quantum computing courses and educational resources for quantum computing students in South Africa, assessing their target levels, educational prerequisites, structure, and content.
The investigation identifies offerings from universities, online platforms, and research institutions, categorising them by complexity: introductory, intermediate, or advanced.
Prerequisite knowledge in linear algebra, programming, and quantum mechanics is analysed to determine accessibility. Course structures (e.g., lectures, workshops, hands-on projects) and core topics (e.g., qubits, quantum algorithms, error correction) are examined to evaluate pedagogical approaches. The findings aim to guide prospective learners
and highlight the gaps in South Africa’s quantum education landscape.

Speakers: Coral Featherstone (CSIR), Laing Lourens (CSIR), Mr Nyameko Lisa (CSIR)

143 Over - Reliance on Simplified Physics Model: Students Explanation in Optics

Physics is about making sense of the world around us. Try explaining phenomena. The way it proceeds is by modelling – Hastens describes this – two parts (theory and experiment). Modelling is about simplifying complexity – essentially by reducing to simpler forms. However, as mentioned by Einstein [?] - the description must be simple but not too simple. Therefore, modelling is to make sense of the physical world by interpreting the relationships that emerge from the model and relating these to the physical world.
In physics, the modelling approach is used to explain the real-world, constructing conceptual models from observations. The challenge lies in accurately describing natural phenomena, as the complex world requires breaking it down into simpler models. However, oversimplifying the model can lead to different descriptions of the problem at hand.
Oversimplification will not explain things adequately and will not lead to sense-making. This pitfall is often seen where physics students divorce their experience from what they learn in physics. For example, - discuss various examples where this is the case – example in mechanics – “feel two forces adding up to zero” – you feel a lot! This is because of incorrect identification of Newtonian force with is felt. Similarly, with explanations of rotational motion in terms of centripetal only. So called frictions force feels pretty real.
The present, broad programme of work aims to map out the Reliance on Simplified Physics Model: Students Explanation in Optics in terms of (1) choosing the appropriate model of light and (2) recognizing the extent to which a top-down component is necessary. To this end, an instrument Models and Perceptions in Optics Questionnaire (MPOQ), is being constructed and administered to the broader programme.
The present talk reports on some of the main work that has been carried out in terms of analysing and reporting the finding of the questions to students in South Africa. Specifically, we report on three questions: the first question involves the directionality of light travel with respect to the eye, the second question centres around refraction while the third question involves the observed size of the moon. Each question is framed as a debate among a group of posited students, each of whom offers a different explanation. Respondents must choose the explanatory option “with which they most closely agree” (Forced Choice Responses), and more importantly, are then asked to explain the reasons for the choice (Free Writing Responses). The FCR’s are analysed by simple tallying while the FWR data are analysed using a grounded theory method.
The talk will present the findings of the three questions which administered to a (mixed) group of 55 first year medical students of UCT in 2019. The result and observation from the analysis will be presented.

Speaker: Ishiyaku Abubakar Mbela (University of Cape Town South Africa)

144 Implications of Separate Marks for Physics and Chemistry in Matric Results

Passing the matriculation examination with a bachelor's status is a prerequisite for admission to most university degree programmes in South Africa. However, many learners struggle to obtain enough Physical sciences and Mathematics scores to be admitted to a full degree program. Such learners are admitted to the extended curriculum program, which equips them with skills to improve their matric results. This study examines the effects of separation of chemistry and physics subjects in the post-matriculation certificate rather than the overall grade in physical science. It uses historical data (11 years) from first-year ECP students to explore the potential benefits. The study identified challenges and implications, including related to students, lecturers, administrators, and higher education stakeholders. Key findings include (1) improved, enhanced subject mastery and informed career choices for students. (2) Improved teaching strategies and curriculum adaptations. The study recommends a pilot trial to investigate the feasibility of separate grades for physics and chemistry in South African schools. Ethical considerations and limitations of the current research are addressed, and the need for careful implementation and ongoing evaluation of the separate grading marks system is emphasized. The conclusion emphasises the potential of this study to significantly impact the physics and chemistry education landscape in South Africa, necessitating further research investigation.

Speaker: VHUTSHILO NEKHUBVI (University of venda)

145 An Approach to Using Arduino in University Practicals

Continuously improving students’ experience of the practical component in formal education is crucial to developing a strong understanding of theoretical concepts whilst staying relevant to technologies used in industry and post-graduate studies. Previous work, within the Nelson Mandela University Physics Department, has shown that innovative practicals can improve and add another dimension to all educational environments.
The focus of this paper is the adaptation and modernization of a 2nd-year practical programme to incorporate an Arduino-based environment. The ease of access to Arduino components and software allows students to interact with a wider range of sensors and components. The affordability of the Arduino kits allows one kit to be assigned to a pair of students, thus enhancing student engagement with the practical. Further advantages of this adapted practical programme include the ability to improve student understanding of electrical diagrams, coding, sensor sensitives and report writing skills.
The programme is run as three structured practical sessions where the students are introduced, under supervision, to Arduino technology including the Arduino UNO, LED’s, push buttons, an LCD, a temperature and humidity sensor and the software, Arduino IDE. Students are then required to complete a ‘Coding Challenge’ which requires them to build an Arduino-based system to solve a supplied scenario. The ‘Coding Challenge’ uses the knowledge covered in the practical sessions and as well as requiring independent learning skills to incorporate a component not covered in the structured sessions. Finally, students are required to demonstrate their systems and write a comprehensive report.

Speaker: Elizabeth Hagemann (Nelson Mandela University)

Physics for Development, Education and Outreach

Convener: Buyi Sondezi (University of Johannesburg)

Physics of Condensed Matter and Materials

Physics of Condensed Matter and Materials 2

Theoretical and Computational Physics: Session 6

Convener: Prof. Azwinndini Muronga (Nelson Mandela University)

146 Discriminating multiprong jet substructure

A wide array of jet substructure based techniques have been used to discriminate large-radius jets coming from the hadronic decay of top quarks against those from light quark or gluons. However, discriminating jets with more than three-prongs have been much less explored. In this work, a new physics signal of a boosted right handed heavy neutrino decaying to a top-bottom quark along with a charged lepton is investigated. The aim is to see which jet substructure observables can be sensitive to identify this signal over the multijet and top quark pair production background processes.

Speaker: Hannah van der Schyf (University of Witwatersrand)

147 Probing the Dead Cone using the Lund Jet Plane

In high-energy particle collisions, high-momentum quarks and gluons (collectively called partons) are emitted from the colliding particles. As these partons move away from the collision point, they transfer their energy to multiple lower energy particles in a cascading process known as a parton shower. Eventually, the low-energy partons combine to form hadrons, which are collected into a jet. To study the evolution of such jets, we exploit a jet substructure observable known as the Lund Jet Plane (LJP), which maps the momentum and angular separation of emissions originating from a jet-initiating quark. This approach is useful for probing the Dead Cone phenomenon, a predicted suppression of soft-gluon radiation around the forward axis of a radiating massive quark. We present results from an analysis of the emission density within the LJP of bottom-tagged jets generated in PYTHIA8 simulations. Furthermore, we discuss opportunities for extensions to heavy-ion collisions where medium-induced radiation is expected to fill the Dead Cone region, providing a tool to isolate and characterize the high temperature phase of the Quark-Gluon Plasma.

Speaker: Ofentse Matlhakola (University of the Witwatersrand)

148 HBA-XGBoost: Honey Badger Algorithm with XGBoost Model for Residual Demand Forecasting

Abstract

Accurate forecasting of residual electricity demand is crucial for enhancing energy planning, grid reliability, and the integration of renewable energy sources. Traditional statistical models often struggle with the complex, nonlinear patterns inherent in electricity demand, giving rise to the need for more robust machine-learning approaches. This paper proposes a novel forecasting framework, HBA-XGBoost, which integrates the Honey Badger Algorithm (HBA) with the Extreme Gradient Boosting (XGBoost) model to optimise forecasting performance. A comprehensive feature engineering pipeline, including temporal decomposition and Fourier analysis, captures the data's daily, weekly, and seasonal variations. The hyperparameters of the XGBoost model are finely tuned using the Honey Badger Algorithm, a swarm intelligence optimisation technique inspired by the foraging behaviour of honey badgers. Experimental evaluation is conducted on historical South African energy demand datasets, divided into training, testing, and out-of-sample validation sets. The results demonstrate that the proposed HBA-XGBoost framework achieves superior predictive accuracy, yielding lower Mean Absolute Error (MAE) and Root Mean Squared Error (RMSE) compared to conventional methods. These findings highlight the potential of synergising metaheuristic optimisation with machine learning models for reliable residual demand forecasting in emerging smart grid infrastructures.

Keywords: residual demand forecasting, XGBoost, honey badger algorithm, machine learning, metaheuristic optimisation, renewable energy integration, smart grids.

Speaker: Pfano Nemakonde

149 Numeric exploration of Non-trivial emergent phenomena in Quark-Gluon Plasma

With the ultimate goal of analysing probe quarks in a Quark-Gluon Plasma via the AdS/CFT correspon-
dance, we explore here the motion of fundamental strings in a curved target spacetime. Specifically, our goal will
be a target space of AdS5 −Schwarzschild, which under the correspondance is dual to a conformal field theory
approximating Quantum Chromodynamics. We will model both the case of a heavy, on-mass-shell quark, corre-
sponding to a string with endpoints fixed at the horizon of a black hole and at the boundary of AdS spacetime,
as well as a light, off-mass-shell quark, which corresponds to a string with one endpoint fixed on the horizon
and the other free to fall. In either case, modes on the string are excited by the black hole, giving rise to motion
of the endpoints of the string, dual to the Brownian motion of the probe quarks in the boundary theory.
We will begin with the analytic results for the equations of motion of these strings under the relavent
boundary conditions, where available in the cases of flat and AdS3 −Schwarzschild target spacetimes, and make
use of tools built into Wolfram Mathematica to numerically solve the same equations of motion in the
remaining case. This will allow comparison between the numeric and analytic cases, allowing us to verify the
results of the numeric simulations. Once agreement has been established, we will extend this to the cases for
which there are no analytic solutions, and interpret the results thereof. Finally, we will then be able to extract
observables relevant to the behaviour of the probe quarks from these solutions.

Speaker: Nia O'Callaghan (University of Cape Town)

150 Parameterizing the Geometry of the QGP on an Event-by-Event Basis

Ultra-relativistic heavy-ion collisions create a nuclear fireball that serves as a powerful laboratory for probing the frontiers of Quantum Chromodynamics (QCD). In recent years, there has been growing interest in the study of small collision systems—such as proton-proton ($pp$) and proton-nucleus ($pA$) interactions—at facilities like RHIC and the LHC. Many of the assumptions underlying the energy loss formalism developed in the Djordjevic-Gyulassy-Levai-Vitev (DGLV) model, break down in these small systems. In this work, we present an extension of the DGLV formalism that specifically accounts for the unique features of small system dynamics. This is achieved by relaxing the large formation time approximation and introducing an additional correction term that accounts for short path lengths in the medium. By relaxing these assumptions, one encounters a more intricate analytic structure for the energy loss, and thus increased computational demands; we address this challenge by developing a novel numerical scheme. Our approach accurately parametrizes the geometry of the quark-gluon plasma (QGP), resulting in a dramatic computational speedup—improving efficiency by up to seven orders of magnitude.

Speaker: Mr Coleridge Faraday (University of Cape Town)

12:30 PM Breather

12:35 PM Lunch

1:45 PM Breather

Plenary

2:35 PM Breather

Applied Physics

Convener: Philippe Ferrer (Wits)

151 Automated photovoltaic module imaging for high throughput data capture and analysis

Photovoltaic (PV) module imaging has become a critical tool for assessing the performance, reliability, and degradation of PV modules. Automated imaging systems that use advanced hardware and image processing software tools allow for efficient high-throughput data capture across large-scale solar installations. These systems use different imaging techniques such as visible light (RGB) imaging, ultraviolet fluorescence (UV-F) imaging, electroluminescence (EL) imaging, and line sensor scanning. These imaging techniques allow for the detection of faults or anomalies in PV modules. We report on a project focussing on the development of a system for high throughput visual and UV-F imaging of PV modules deployed in utility-scale PV plants. The work follows a two-step approach whereby two systems will be built. The first-step consists of a laboratory-based imaging system to test proof of concept. The system will utilise an Arduino MEGA 328P microcontroller for position control and a Raspberry Pi 5 8 GB as the microprocessor for sensor control, image capturing and storage. The images will later be processed through stitching and basic visual classification.The second-step will use techniques determined to be effective from the initial system to build an onsite imaging and sensing system that allows for rapid large-scale image capture for further image processing and classification. This allows for more data and images to be captured, and thus processed as opposed to manual methods. At the same time, has a much greater resolution as opposed to drone imaging.
This paper will present the design, manufacture, optimisation and preliminary results from the laboratory-based system.

Speaker: Matthew Sivewright (Neslon Mandela University)

152 What are the most suitable basic solar irradiance models for Southern Africa?

Solar irradiance modelling is critical for determining local solar energy potential. Several past studies have analysed the more easily attainable Global Horizontal Irradiance (GHI) within Southern Africa. However, less research has been carried out on the physically more useful Direct Normal Irradiance (DNI) and Diffuse Horizontal Irradiance (DHI). This study aims to alleviate this by investigating for these local sites simple clear sky models which are solely dependent on the solar zenith angle and identifying the appropriate scaling parameters for DNI and DHI. The accuracy of the Meinel model for DNI and a Logarithmic model for DHI are evaluated and compared to the Power Law model more commonly used in solar irradiance modelling. The model evaluations were conducted using 1-minute resolution data taken from 5 stations within the SAURAN network: Vanrhynsdorp, Richtersveld, Graaff-Reinet (all located in South Africa), Gaborone (Botswana) and Windhoek (Namibia) over the period 2014-2021, with a minimum of 13 clear sky days selected per station covering all seasons.

Speaker: Ms Sindiswa M. Figlan (University of Johannesburg)

153 Physics-based modelling and simulation of lithium-ion battery capacity fade and degradation

Lithium-ion batteries (LIBs) have revolutionised the automotive industry (mainly electric vehicles)as a sustainable energy storage solution for electric vehicles due to their high-power and energy density. Their widespread adoption is crucial for achieving global decarbonization goals and reducing dependence on fossil fuels. However, the degradation of LIBs over time remains a challenge, leading to capacity fade and loss of battery performance, which ultimately affects the their lifespan and efficiency. Hence, it is essential to understand the aging processes in LIBs for improving battery design and optimising battery operation. This study employs physics-based electrochemical models that are implemented in an open-source battery simulation package – PyBaMM to understand the impact of high charging rates on capacity fade and degradation (solid electrolyte interphase growth and lithium-plating). The simulation was performed for 50, 100 and 200 cycles, using charging rates of 2 C, 8 C, 16 C, 20 C. Results indicate that higher charging rates exhibits faster aging of the battery. At moderate rates (2C, 8C), the SEI growth dominated during the initial cycleswhile at higher C-rates (16 C-20 C) lithium-plating became the primary contributor to capacity loss. Batteries charged at a higher current 20 C showed a 50% capacity loss within 100 cycles.
Keywords: Lithium-ion batteries, modelling, degradation, capacity loss, C-rate, solid electrolyte interphase.

Speaker: Patel Sana (University Of Venda)

Astrophysics & Space Science: Astrophysics

154 Neutrino Emission from Bright Blazar Flares

Blazars, a subclass of active galactic nuclei, have emerged as candidates for the sources of very-high-energy astrophysical neutrinos observed by the IceCube Neutrino Observatory. Notable temporal and spatial coincidences, particularly the event IceCube-170922A coinciding with a flare from TXS 0506+056, have sparked interest in the connection between these objects and neutrino production. In this study, we utilize the time-dependent lepto-hadronic code OneHaLe to fit the spectral energy distributions and light curves of bright gamma-ray flares from a sample of blazars detected by Fermi-LAT. In comparison to the calorimetric estimates of neutrino detection rates provided by Kreter et al. (2020), we model the flares with variations in proton injection spectra, allowing for a full assessment of neutrino production. Our findings reveal an overestimation in neutrino production rates using the calorimetric approach, typically by a factor of approximately 10, in cases where gamma-ray emissions are dominated by proton-synchrotron radiation. We also show that the non-detection of neutrinos during these flares does not necessarily imply a lack of relativistic protons within the jet, and shows that future-generation observatories may be able to detect the presence of said protons.
The work to be presented has been published in Robinson & Böttcher 2024 ApJ 977 42 (DOI 10.3847/1538-4357/ad8dce).

Speaker: Joshua Robinson (North-West University)

155 Astrophysical origin of the highest-energy neutrino event

Recently the KM3NeT neutrino telescope detected the most-energetic neutrino event ever, dubbed KM3-230213A, at an estimated energy of 220 PeV. Given its near horizontal direction and exceptionally high energy, the most likely explanation is that the muon resulted from interaction of a muon neutrino of cosmic origin. In this talk I will explore an astrophysical source origin, both transients and steady, of this intriguing event.

Speaker: Soebur Razzaque (University of Johannesburg)

156 Probing Dark Matter Signatures in IceCube Astrophysical Neutrino Data

Dark Matter (DM) makes up a significant portion of the universe's mass-energy content, yet its fundamental nature remains elusive. Neutrinos are nearly massless particles that interact weakly with ordinary matter and may provide evidence of subtle interactions with DM. One possibility is that dense DM spikes, which form around supermassive black holes, can weaken the high-energy neutrino flux emitted from the host galaxy. Therefore, observing high-energy neutrinos from active galactic nuclei (AGN) can offer a unique opportunity to investigate these interactions. Recent observations of point-like neutrino sources, such as the blazar TXS 0506+056 and the radio galaxy NGC 1068 by the IceCube observatory, present a valuable chance to explore DM interactions beyond standard astrophysical scenarios. In this context, we aim to constrain the neutrino-DM scattering cross-section by combining data from all these sources, leveraging the public information provided by IceCube.

Speaker: Khushboo Dixit (Centre for Astro-Particle Physics, University of Johannesburg)

Nuclear, Particle and Radiation Physics-1

Nuclear, Particle and Radiation Physics-2

157 Strategy for Particle Physics: Opportunities for South Africa

The field of collider particle physics is at a pivotal juncture, with global debates intensifying over the direction of future accelerators and large-scale international collaborations. As the scientific landscape continues to evolve, it is imperative for the global particle physics community to refine its strategic priorities and align around shared goals. The European Strategy for Particle Physics, last updated in 2020, is slated for revision in 2026, providing a timely opportunity for reflection and repositioning. While the High-Luminosity LHC defines the short- to mid-term horizon, proposed next-generation electron-positron colliders—including the ILC, FCC-ee, and CEPC—stand as prominent contenders for the future. Additionally, new bridge projects and alternative accelerator concepts are gaining traction, particularly at CERN. This talk will review the current global landscape and explore how South Africa can strategically position itself within these developments, highlighting potential avenues for participation, leadership, and impact in the next era of particle physics.

Speaker: Bruce Mellado (University of the Witwatersrand and iThemba LABS)

158 Detector Research and Development projects for future High Energy Physics experiments

The European Strategy for Particle Physics stimulated the preparation of the European Detector Roadmap document in 2021 by the European Committee for Future Accelerators ECFA. This roadmap, defined during a bottom-up process by the community, outlines nine technology domains for HEP instrumentation and pinpoints urgent R&D topics, known as Detector R&D Themes (DRDTs). Task forces were set for each domain, leading to Detector R&D Collaborations (DRDs), now hosted at CERN. Eight DRD collaborations have been established and set up their collaboration structures, with some having already started their R&D
I will give a brief overview of the current status of DRD collaborations covering detector developments in the field of gaseous detectors, noble liquid detectors for rare event searches, semiconductor detectors, photodetectors and concepts for particle ID, quantum sensors, calorimetry, electronics for HEP instrumentation and mechanical and integration aspects. Many of these topics would be of great interest to South African particle physics community to plan their involvement in future accelerator projects such as CEPC, FCC as well as in technology transfer and applications in other fields.

Speaker: Rachid Mazini (School of Physics, The University of the Witwatersrand)

Photonics: Photobiomodulation & Biomedical Applications

Convener: Mitchell Cox (University of the Witwatersrand, Joahnnesburg)

159 <i>In</i> <i>Vitro</i> Effects of Blue Laser Light as an Antimicrobial Agent on Microbial-Infected Fibroblast Cells

In Vitro Effects of Blue Laser Light as an Antimicrobial Agent on Microbial-Infected Fibroblast Cells

<u>Francis Obeng Brenya¹ and Nicolette Nadene Houreld¹

¹Laser Research Centre, Faculty of Health Science, University of Johannesburg, Johannesburg, South Africa

Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes are key pathogens that delay healing and pose challenges due to their antibiotic resistance. Antimicrobial photobiomodulation (aPBM) using blue light (400-470 nm) has been shown to have antibacterial properties; however, its effects on mammalian cells are not well understood. We investigated the effect of blue laser light (470 nm, 82.7 mW/cm², 10 J/cm², 2 min) on bacteria-infected BJ-5ta fibroblast cells. BJ-5ta cells were co-cultured for 24 h with each of the three bacterial strains (1.50 x 10³ CFU/mL) and then exposed to blue light. Fibroblast cell viability and bacterial colony counts were assessed 24 h post-aPBM. Control cells (0 J/cm²) infected with S. aureus exhibited 95% fibroblast cell viability and increased bacterial counts (1.80 x 10⁵ CFU/mL). Control cells (0 J/cm²) infected with S. pyogenes and P. aeruginosa showed 89.5% fibroblast cell viability, with bacterial counts increasing to 3.00 x 10⁵ and 2.36 x 10⁵ CFU/mL, respectively. In irradiated (10 J/cm²) BJ-5ta cells infected with S. aureus, P. aeruginosa, and S. pyogenes, fibroblast cell viability was 89.2%, 94.6%, and 77.6%, respectively. As compared to the controls, bacterial counts decreased to 1.30 x 10⁵ CFU/mL, 1.35 x 10⁵ CFU/mL, and 1.20 x 10⁵ CFU/mL, respectively. Blue light (470 nm, 82.7 mW/cm², 10 J/cm²) induced bacterial death while preserving fibroblast cell viability after a single exposure. aPBM has the potential to address the medical challenges associated with infected wounds and open new avenues for future research.

Speaker: Mr Francis Obeng Brenya (Laser Research Centre, Faculty of Health Science, University of Johannesburg, Johannesburg, South Africa)

160 Optimizing Photobiomodulation Parameters for Tenogenic Differentiation

Tendons are frequently damaged by acute injuries, such as sports injuries or chronic overuse and age-related degeneration. Native tendon healing is lengthy and ineffective due to the tissue's inherently low cellularity, limited vascularization, and low metabolic activity of resident tenocytes. Natural healing is often accompanied by fibrosis, adhesion formation and re-injury is common. Current treatment options focus on symptom management and gradually strengthening the tissue over time. Mesenchymal stem cell (MSC) therapy offers a promising alternative due to the ability of MSCs to proliferate, differentiate into tenocytes and produce ECM (extracellular matrix) components to facilitate tendon repair. Photobiomodulation (PBM), uses specific light wavelengths to stimulate intracellular chromophores and activate various cellular functions. PBM has demonstrated potential in enhancing stem cell viability and proliferation, as well as tenogenic differentiation and ECM production. Despite this, there is a lack of standardized PBM parameters (wavelength and fluency) for tenogenic differentiation, hindering reproducibility, cross-study comparisons and translation into clinical trials. This study aimed to evaluate the potential of PBM to enhance tenogenic differentiation and to determine the optimal PBM parameters. Adipose-derived mesenchymal stem cells (ADMSCs) were irradiated using 525 nm, 825 nm, and a combination of both wavelengths at fluences of 5 and 10 J/cm². Prior to PBM treatment, the stem cell nature of the ADMSCs was confirmed via immunofluorescent detection of CD44, CD90, and CD166. Post-differentiation assessments included morphological analysis (May-Grünwald-Giemsa staining), cytotoxicity, and proliferation assays. Tenogenic differentiation was evaluated via gene expression (Scleraxis, Tenomodulin, Collagen I, Tenascin-C, and Biglycan) and immunofluorescence staining (Scleraxis, Tenomodulin, and Collagen). The results confirmed the stemness of the ADMSCs and showed that tenogenic differentiation, particularly when combined with PBM, enhanced cell viability, proliferation, and expression of tenogenic markers, without significant morphological changes. These findings highlight PBM as a promising adjunct to improve tenogenic outcomes.

Speaker: Brendon Roets (University of Johannesburg)

161 Synergistic Effect of Photobiomodulation and Vanillin on Energy Metabolism in Diabetic Wounded Cells In Vitro

Delayed wound healing is among the major peripheral complications of diabetes. Synergistic treatment of diabetic wounds with phytochemicals and non-invasive techniques such as photobiomodulation (PBM) has shown promising results. Cells rely on glucose metabolism for the generation of adenosine triphosphate (ATP) for energy utilization. However, glucose metabolism is altered in diabetic wounds and contributes to delayed healing. The present study investigated the synergistic effect of vanillin and PBM and their modulatory effect on energy metabolism in diabetic wounded (DW) modeled fibroblast cells (WS1). DW cells were treated with vanillin and vanillin + PBM (at 660 nm with a fluence of 5 J/cm² for an irradiation time of 780 s). Controls consisted of WS1 cells, untreated DW cells, and DW cells treated with PBM. There was an increase in the activities of fructose-1,6-biphosphatase, glucose 6-phosphatase, and E-NTPDase, with concomitant suppressed activities of glutathione reductase and glyoxalase, following induction of DW. Treatment with vanillin (12 ug/mL) and vanillin (6 ug/mL) + PBM significantly reversed these activities and closed the wounds while maintaining the cells’ morphology. These results indicate the synergistic therapeutic effect of vanillin + PBM on the management of diabetic wounds, with vanillin (6 ug/mL) + PBM displaying the best effect.

Speaker: Dr Ochuko Erukainure (University of Johannesburg, Doornfontein campus, Johannesburg)

Physics for Development, Education and Outreach

Convener: Derek Fish (University of Zululand)

Physics of Condensed Matter and Materials

Physics of Condensed Matter and Materials 2

Theoretical and Computational Physics: Session 7

Convener: Dr Joseph Anosh (Witwatersrand)

162 Comparative Study of Neutron and Proton Halo Breakup Cross Sections

We use the Continuum Discretized Coupled Channels (CDCC) method to study in detail the similarities and differences between neutron and proton halo breakup cross sections including total, nuclear, and
Coulomb contributions in the breakup reactions of 8B→7Be+p and 8Be→7Be+n on various target nuclei (28Si, 120Sn and 236U). Our preliminary results reveal that the neutron halo breakup cross sections are generally larger than those of the proton halo. Additionally, we find that continuum-
continuum couplings are stronger in the neutron halo breakup than in the proton halo breakup.

Speaker: Dr Lucas Vusi Ndala (University of South Africa)

163 Azimuthal modulational instability in quantum fluids of light

In this study, we investigate the azimuthal modulational instability (MI) of bright vortex ring solitons in spinor exciton-polariton condensates. Considering the distance where the maximum vortex intensity occurs, we derive a quasi-one-dimensional azimuthal Gross-Pitaevskii equation describing the vortices, and perform a stability analysis in Fourier space. By examining the MI growth rate spectra of azimuthal modes, we show that vortices become unstable below a critical wave number, leading to their breakup into a ring of filaments. Additionally, we analyze vortex-antivortex configurations, and find to that the strength and sign of spin-orbit coupling (SOC) dramatically influences the stability and symmetry of vortex states within the adiabatic approximation. Employing an analytical approach based on a non-conservative Euler-Lagrange formalism for complex Ginzburg–Landau equations (cGLE), we derive explicit expressions for stationary bright vortex ring solitons under photonic SOC induced by TE-TM splitting. These solutions serve as initial conditions for numerical simulations of coupled Gross-Pitaevskii equations, revealing regimes where cylindrical symmetry spontaneously breaks, resulting in core deformation, fragmentation, or collapse. The results demonstrate that photonic SOC acts as a destabilizing force, driving pattern formation and symmetry breaking in polariton fluids.

Speaker: Mr Edmond Bakang Madimabe (Botswana internation university of science and technology)

3:40 PM Afternoon Tea

Poster Session

Council Metting with HOD's

WAADD

Thu, July 10

Plenary

9:15 AM Breather

Applied Physics

Convener: Nicolas Thantsha

164 Design and Experimental Evaluation of an Archimedes Screw Hydro Turbine (ASHT) for Rural Sustainable Energy Application

A significant portion rural Africa still lack access to affordable, sustainable and modern energy, causing a knock-on effect on the development of education, agriculture, healthcare, business and transportation, ultimately lowering the rural quality of life. Towards a sustainable solution in meeting the rural Southern Africa energy demand, there is a need for indigenous development and implementation of suitable technologies. In this context, we present on the design and experimental evaluation of an Archimedes Screw Hydro Turbine (ASHT) prototype fabricated using recycled plastic for rural sustainable energy application. Being a device, that works mechanically to produce electrical energy from the flow of water with low head and flow rates, ASHT is suitable for use in water bodies such as running streams and rivers common in rural Africa as well as with irrigation channels, all representing a renewable energy source. Design consideration for optimised turbine performance included among other variables, the pitch of the screw, inner diameter of the screw, number of screw blades, angle of the screw, rotational speed, water flow rate and head. ASHT offer several advantages to include low maintenance, simple installation and maintenance, and operation at low head and flow rate. We envisage ASHT application in hybrid configuration in combination with solar technologies.

Speaker: Enock Jonathan

165 Proactive Equipment Monitoring Using Vanilla LSTM for Predictive Maintenance at iThemba LABS

iThemba LABS operates complex scientific equipment including particle accelerators where unexpected failures can disrupt critical experiments for extended periods. We present a predictive maintenance framework based on Vanilla LSTM networks that analyzes multivariate time-series sensor data to anticipate equipment failures. The model was trained on operational data from 2021-2024, monitoring key parameters like voltage, vibration, and pressure across various systems. Our approach demonstrates significant improvements over traditional methods, achieving a 75% F1-score in failure prediction with up to 72 hours warning time. The framework includes an interpretable failure scoring system that helps technicians prioritize maintenance interventions. Practical implementation challenges at iThemba LABS, such as handling noisy sensor data in high-vibration environments, were addressed through careful feature engineering and model optimization. The methods developed are particularly relevant for physics laboratories and other facilities operating sensitive, high-value equipment.

Speaker: Edward Nkadimeng (NRF-iThemba LABS)

166 POWER LAW MODEL (PLM) APPROACHES TO PREDICT THE PERFORMANCE OF A SMALL-SCALE PV SYSTEM

This paper proposes a mathematical approach to predict the real-time performance of the small-scale photovoltaic (PV) system mounted at the Arcadia based on the power law model (PLM), commonly used to predict the I-V curves of solar cells in standard test conditions (STC). The shape parameters involved in the PLM known as m and µ in this study were determined using experimental data collected under normal weather conditions (irradiation and temperature) based on the Newton-Raphson algorithm iterative method. From the investigations performed on the MATLAB platform, the obtained results reveal that the shape parameters do not strongly depend on temperature and irradiation as shown by the low correlation of 0.296 and -0.110 respectively for µ and -0.201 and -0.188 respectively for m . We also notice that the shape parameters are strongly correlated to the output electrical parameters: µ is strongly correlated to the fill factor with a correlation factor of 0.958 while m strongly depends on voltage with a correlation factor of 0.784. Additionally, this approach predicts with high accuracy in real-time, the output electrical parameters of the PV system with the mean value of R2, RMSE, and correlation r of about 0.99, 3.07 %, and 0.99 respectively. Furthermore, we noticed that the parameter µ varies between 0.8 and 1 during winter and from 0.5 to 0.8 in summertime, while m fluctuates between 10 and 20 during winter and from 10 to 25 during summertime. This approach offers high accuracy because the shape parameters take into account the dynamical behavior of the losses (internal and external), such as recombination effect, series and shunt resistance in each PV module, which varies under different weather conditions. The limitation of this model is that we do not have enough information that links the shape parameters to the electrical parameters such as ideal factor, saturation current, shunt, and series resistance to perform the qualitative investigation based on the shape parameters. Additionally, we do not have a mathematical formula that can facilitate the determination of the shape parameters to predict the performance of the PV system.

Speaker: Dr Abraham Dimitri Kapim Kenfack (Tshwane University of Technology)

Astrophysics & Space Science: Space Science Session 4

Convener: Zama Katamzi-Joseph

167 Investigating the latitudinal-dependent solar differential rotation rate using SDO/HMI Dopplergrams

The solar photospheric differential rotation rate has novel implications to the structure of the heliospheric
magnetic field. The period of the solar poles is ~ 35 days, and ~ 25 days at the equator.
In this study, the Doppler shift (either blue or red) of 116 Dopplergrams from the Helioseismic
and Magnetic Imager instrument on board the Solar Dynamics Observatory are investigated to
experimentally determine the photospheric differential rotation rate at different solar latitudes. A
model is developed to describe the variation of surface speed with solar latitude. The results are
compared to well-established models in the literature and shows strong consistency in trend and
behaviour. The findings confirm the latitudinal differential rotation of the Sun. The developed
model shows a deviation of less than 10% when compared to established models in the literature,
demonstrating its accuracy and consistency. This is particularly significant considering the difference
in time scales, with the models in the literature using data spanning more than a decade,
compared to the model developed using approximately an hour and a half of collected data. This
study not only confirms the theoretical expectations regarding solar rotation but also demonstrates
the effectiveness of Doppler spectroscopic analysis and space-based solar observations in studying
solar dynamics. The results contribute to a broader understanding of solar behaviour.

Speaker: Thembalethu Zulu

168 Modelling the antiproton modulation related to AMS-02 observations between 2011 and 2021

In this study, the previously established set of modulation parameters used to reproduce PAMELA
and AMS-02 proton observations between 2006 and 2022 is applied in the 3D steady-state drift
numerical model to simulate antiproton spectra observed by AMS-02 detector between 2011 and
2021. In this way, the only differences between galactic protons and antiprotons simulations in
the model remain their local interstellar spectra (LIS) and the sign of their charges. This is a better
approach to antiproton modelling, especially when novel insights into potentially new physics
are sought. Surprisingly, the simulated solar modulation effects on antiprotons were found to be
much less pronounced than on protons at the same rigidity. For example, the computed intensity
of antiprotons at ~ 1 GV was found to increased by ~13% between 2011 and 2019, whereas for
protons at the same rigidity the intensity increased by ~ 86%. This result has now been confirmed
by precise AMS-02 observations done at the same position around the Earth and over a long period.
In this study it will be shown how the antiprotons LIS at lower rigidities intriguingly resembles
the shape of the modulated spectra, and how this greatly influences the adiabatic energy losses
these particles experience deep inside the heliosphere.

Speaker: THABO MAHLATJI (NWU Student)

169 Simulating cosmic ray diffusion coefficients in synthetic compressive magnetic turbulence

In order to reliably estimate cosmic ray (CR) transport effects due to turbulence in the heliospheric
magnetic field (HMF), and to validate existing diffusion theories (see, e.g., Engelbrecht et al., 2022,
for a review), direct simulations, which involve solving the Newton-Lorentz equation numerically,
may be employed (e.g., Els and Engelbrecht, 2024). Prior work, guided by turbulence conditions
observed in the inner heliosphere, has largely focused on CR transport due to turbulence transverse
to the background magnetic field. However, CR transport in the outer heliosphere, including in
the heliosheath (HS), where HMF turbulence has been observed to have a compressive component
(e.g., Fraternale et al., 2019), has, to date, received comparatively little attention. In this work,
an approach to modelling HMF turbulence with an arbitrary compressive component, based on
the synthetic turbulence model of Tautz and Dosch (2013), is suggested. Furthermore, turbulence
parameters which may be expected in the HS are inferred from available analyses (e.g., Fraternale
et al., 2019; Zhao et al., 2024). These parameters are then used as inputs for the particle pusher code
detailed by Els and Engelbrecht (2024), modified so as to account for the presence of compressive
turbulence, from which estimates for CR transport coefficients due to HMF turbulence conditions
in the HS are calculated.

Speaker: Jonathan Troskie

Nuclear, Particle and Radiation Physics-1

170 Study of low-medium spin states in ¹⁵⁶Er

This work aims to shed light on the low to medium spin states of ¹⁵⁶Er by analysing coincidence relationships following the ¹⁴⁷Sm(¹²C, 3n)¹⁵⁶Er reaction at 65 MeV. This experiment was performed using the AFRODITE array of iThemba LABS. A level scheme has subsequently been built using this information and a total number of 9 bands has been observed. The current work has not only observed almost all the rotational bands reported by the previous work but also suggests some changes. The implications of the new findings are therefore discussed.

Speaker: Ms N.N Khanyeza (University of Pretoria)

171 Investigating the photon shielding factors of the silicate glass system from 1 MeV up to 15 MeV, Using the X-COM and GEANT4 simulating software

This study investigates the radiation shielding capabilities of silicate glasses (S1–S4) across photon energies ranging from 1 to 15 MeV. Using Phy-X, XCOM, and GEANT4 simulations, key shielding parameters were estimated, including the mass attenuation coefficient (MAC), linear attenuation coefficient (LAC), half-value layer (HVL), tenth-value layer (TVL), mean free path (MFP), and effective atomic number ($Z_{\text{eff}}$). The glasses exhibited maximum photon shielding performance at 1 MeV, with LAC values of 0.18398, 0.17842, 0.17696, and 0.14718 cm$^{-1}$ for S1 through S4, respectively.

The LAC was observed to decay exponentially with increasing energy, while the MAC began to decrease exponentially around 4 MeV. These reductions in shielding effectiveness are attributed to increased Al$_2$O$_3$ content and decreased CaO content within the glass matrix. Additionally, HVL and TVL were analyzed in relation to material density. As density decreased from 2.90 to 2.76 g/cm$^3$, HVL increased correspondingly, with values at 1 MeV measured as 3.76758 cm (S1), 3.88481 cm (S2), 3.91705 cm (S3), and 3.97937 cm (S4). The HVL also increased significantly with photon energy, nearly tripling between 1 and 15 MeV.

These results provide a comprehensive assessment of silicate glasses as potential materials for high-energy radiation shielding applications, highlighting their energy-dependent attenuation behavior and compositional influence on shielding performance.

Speaker: Mr Mfundo Zuma (University of Zululand)

172 The photon strength functions from (p, γ) capture reactions.

Abstract:
In the 1970s and 80s, (p, $\gamma$) reactions [1] were successfully utilized to measure the Photon Strength Function (PSF) using the Average Resonance Proton Capture (ARPC) Method [1, 2]. In this research, these reactions have been used to extract the slope of the PSF from the $^{50}$Cr(p, $\gamma$)$^{51}$Mn proton capture data using the Shape method [3] with no s-wave resonance spacing data ($D_{0}$). The reactions populated entry states between the 5.3 MeV proton and 13.7 MeV neutron separation energies, which decayed through primary $\gamma$-ray transitions to low-lying discrete states. For the proof-of-principle $^{50}$Cr(p, $\gamma$)$^{51}$Mn reaction, the Tandetron accelerator at iThemba LABS delivered proton beams of 2500 to 2740, 2760 to 3000, 3675 to 4100 and 4100 to 4500 keV in intervals of 20-25 keV with the primary $\gamma$-rays emitted being detected using a segmented Clover detector. A total of 64 $\gamma$-ray spectra were collected and with the use of the ARPC method were summed into ARPC spectra, which cover 260, 260, 425 and 400 keV excitation-energy bins. Using the average intensities of the primary $\gamma$-rays from these ARPC spectra, the slopes of the PSFs to 1/2$^{-}$, 3/2$^{-}$, 5/2$^{-}$ and 7/2$^{-}$ final states of known spin and parity in $^{51}$Mn were extracted. The scaling and sewing techniques of the Shape method were used to determine the shape of the total PSF to 1/2$^{-}$, 3/2$^{-}$, 5/2$^{-}$ and 7/2$^{-}$ final states despite having no spin distribution data. The shape of the total PSF was normalized to the Simple Modified Lorentzian (SMLO) and DM1 Gogny force plus Quasi-Particle Random Phase Approximation (D1M+QRPA) PSF models [2] to obtain the absolute values of the shape of the total PSF. Despite predicting different absolute values, the two models predict slopes that are comparable to each other. The shape of the total PSF shows what might be three low-lying $E1$ structures that could influence nuclei abundance calculations. The $^{50}$Cr(p, $\gamma$) cross sections calculated with the Hauser-Feshbach statistical model by using the total PSF as input when compared with the cross section calculated from direct methods shows good agreement. The level scheme of the $^{51}$Mn compound nucleus was built with several new transitions and states being identified.

Acknowledgments
This work is supported in part by the National Research Foundation (NRF) of South Africa (Grant No: 118846 and REP_SARC180529336567), the Department of Higher Education and Training (DHET) through its New Generation of Academics Programme (nGAP) and Walter Sisulu University (WSU). It is also based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contract No. DE-AC02-05CH11231.

References
[1] B. Erlandsson et al, Nucl Phys A, 343:197–209, (1980).
[2] S. Goriely et al, Eur. Phys. J. A, 55:172 (2019).
[3] M. Wiedeking et al, Phys Rev C, 104(1):014311, (2021).

Speaker: Adivhaho Netshiya (WSU, WITS and iThemba LABS)

173 INVESTIGATING THE PHOTON STRENGTH FUNCTION FOR 61Cu USING 60Ni (p, γ) REACTION AT iTHEMBA LABS

INVESTIGATING THE PHOTON STRENGTH FUNCTION FOR ⁶¹Cu USING ⁶⁰Ni (p, γ) REACTION AT iTHEMBA LABS

The Brink-Axel hypothesis assumes that photo-de-excitation only depends on the emitted γ-ray energy Eγ and not the detailed structure of the initial and final states (spin and parity) involved in the transition as it is the case for photo-excitation process. While the hypothesis is widely used for all PSF energy regions such as the giant dipole resonance (GDR), it remains under investigation for the low energy region [1]. In the present work, this hypothesis will be tested below the neutron separation energy, using for the first time radiative proton capture. An experiment to indirectly measure the photon strength function (PSF) took place at iThemba LABS’s Tandetron facility, to populate excited states in ⁶¹Cu utilizing ⁶⁰Ni(p, γ)⁶¹Cu reaction. The model independent ratio method [2] and the shape method [3] will be used to investigate the statistical γ-ray decay to individual well established discrete states. With the neutron separation energy at 11.7 MeV, populated states with beam energies in the range 2.32-4.32 MeV will confine the study below the particle separation energy.

Data analysis is ongoing, and preliminary results will be presented.

References

1. S. Goriely et al., Eur. Phys. J. A 55, 172 (2019).

2. M. Wiedeking et al. Phys. Rev. Lett. 108, 162503 (2012).

3. M. Wiedeking et al. Phys. Rev.C 104, 014311 (2021).

This research work is supported in part by the National Research Foundation (Grant No:118846, 92600, 90741, 92789 and REPSARC180529336567). It is also based upon work supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contract No. DE-AC02-05CH11231.

Speaker: Mr Tshegofatso Goitseone Modise (UNIVERSITY OF BOTSWANA)

174 The PANDORA Project: Investigating Photonuclear Reactions in Light Nuclei.

The PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) project explores photo-nuclear reactions in light nuclei (A $<$ 60) through both experimental and theoretical studies. This research is particularly relevant to ultra-high-energy cosmic rays (UHECRs), where energy and mass loss primarily occur via electromagnetic interactions between nuclei and the cosmic microwave background, driven by the isovector giant dipole resonance (IVGDR) and it also has profound significance for nuclear physics for reaction calculations, theoretical models and nuclear data benchmarks. A key limitation in current UHECR propagation models is the scarcity of reliable experimental data for critical nuclei. To address this, PANDORA will utilize virtual photon experiments at iThemba LABS and RCNP, as well as real photon experiments at ELI-NP, to extract essential nuclear parameters, including IVGDR cross-sections, E1 strength distributions, and branching ratios for particle decay. The project's first experiment was conducted at RCNP in late 2023, focusing on photo-absorption and charged particle decay in $^{12}$C and $^{13}$C. This study utilized the Grand Raiden spectrometer, SAKRA (a backward-angle silicon detector array), and SCYLLA (a LaBr$_3$ detector array). This presentation will discuss the analysis of these measurements and their implications for UHECR propagation, particularly in refining loss length calculations.

This work is based on the research supported in part by the Japan-South Africa Bilateral Funding from JSPS with a grant number of JPJSBP 120216502 and from NRF with grant number 132993, the National Research Foundation of South Africa through Grants No. 129411, and 118846 and the SARCHI grant number 180529336567 and supported in part by the National Research Foundation (NRF) of South Africa grant number 118846, the Romanian Ministry of Research, Innovation and Digitization, CNCS - UEFISCDI, project number PN-III-P4-PCE-2021-0595, within PNCDI III

Speaker: Jacob Bekker (University of the Witwatersrand, iThemba LABS, South Africa)

175 Simulation of the X-ray and gamma-radiation shielding parameters of the Li2O+Sb2O3+PbO+GeO2 glass materials in the 20 - 300 keV energy range using Phy-X/PSD, XCOM, and Geant4 software programs

Ionizing radiation is used in fields such as medical physics and nuclear research, with concrete and lead commonly serving as shielding materials. However, these materials carry health risks: lead is linked to harmful health effects, while concrete is heavy and susceptible to cracking over time, which raises safety concerns. Additionally, both lead and concrete block visible light, leading to a lack of transparency. Glass emerges as a suitable alternative, being cost-effective, transparent, and free from adverse health effects. In this study, the software programs Phy-X/PSD, Geant4, and XCOM have been employed to investigate the effect of chromium oxide (Cr₂O₃) on the radiation-shielding properties of glass systems with the chemical composition 10Li₂O+(30-x)Sb₂O₃+20PbO+40GeO₂+xCr₂O₃, where x = 0.1, 0.2, 0.3, 0.4, 0.5 mol%. The key properties examined include the linear attenuation coefficient (LAC), mass attenuation coefficient (MAC), mean free path (MFP), half value layer (HVL), tenth value layer (TVL), and effective atomic number (Zeff). These parameters were investigated for energies ranging from 20 to 300 keV. The results show that increasing the Cr₂O₃ content enhances the shielding properties of the examined glass systems. The analysis indicates that the sample with the highest Cr₂O₃ content exhibits the highest LAC and MAC, alongside the lowest HVL, TVL, and MFP, suggesting it offers better radiation shielding capabilities compared to the other samples. Furthermore, the shielding effectiveness of the glass samples was compared to literature data, focusing on the MFP at 100 keV and 200 keV. The findings reveal that the MFP of our samples is lower than that of other reported glass materials, suggesting that the glasses under investigation demonstrate improved attenuation characteristics.

Speaker: Dr Linda Mdletshe (University of Zululand)

176 Coupling the MAGNEX focal-plane detector to the K600 high-resolution magnetic spectrometer for the NUMEN project

The NUMEN (NUclear Matrix Elements for Neutrinoless double-beta decay) project aims to obtain the nuclear matrix elements (NME) to be used as inputs in models to determine the lifetime of neutrinoless double-beta (0νββ) decay, which is related to the absolute mass of the neutrino [1]. This will be achieved by conducting heavy-ion double charge-exchange (DCE) reactions and measuring the cross sections of these reactions for all isotopes that have been identified to undergo 0νββ decay [1]. The occurrence of the 0νββ decay will imply that the lepton number is violated [2]. It is, therefore, very important to determine the NMEs as they will assist in elucidating Physics beyond the Standard Model [2]. The transition operators of the 0νββ decay and DCE reactions have a similar mathematical structure with a combination of short 0νββ decay range Fermi, Gamow-Teller, and rank-2 tensor components [3]. The weights of such components are different, being controlled by the coupling constants in the weak sector and by the energy-dependent isospin, spin-isospin, and tensor coupling strengths for the strong interaction [3]. Therefore, more experimental data are required from a range of incident beam energies for DCE measurements. Additionally, to explore the candidate nuclei of 0νββ decay in a systematic way, more experimental data are required. Previous experiments for the NUMEN project at Istituto Nazionale di Fisica Nucleare-Laboratori Nazionali del Sud (INFN-LNS) have suffered from high signal rate due to the interaction of the target and projectile, which greatly outnumber any potential DCE events. Additionally, the limited energy resolution of the MAGNEX spectrometer for DCE measurements makes it a cumbersome task to decouple transitions of interest relevant to the NUMEN project. Particle-γ coincidence measurements are a plausible attempt at a solution for this problem. Thus, a high-resolution magnetic spectrometer like the K600 at the iThemba Laboratory for Accelerator Based Sciences (iThemba LABS), which is already used for coincidence measurements, is a perfect candidate for baseline measurements especially given that the LNS facility is still under upgrade. However, in its current design, the existing K600 detection system is limited in the detection of heavy ions (e.g. $^{6}\mathrm{Li}, ^{12}\mathrm{C}, ^{18}\mathrm{O}, ^{18}\mathrm{Ne}$) at moderate kinetic energies (≈ 10 MeV/u) and light ions at low energies (≈ 5 MeV/u) [4]. The development of a new low-pressure detection system for the K600 is currently underway to expand the spectrometer research program [4]. Thus, an already existing detection system from the MAGNEX large-acceptance spectrometer at INFN-LNS has been coupled to the K600 to provide a baseline as to how the K600 will operate with a low-pressure detection system. The coupling of the MAGNEX focal-plane detection system with the K600 is also beneficial for other nuclear-structure studies to be conducted with the K600 spectrometer. This talk will present preliminary results from the commissioning experiment, where the K600 was coupled to the MAGNEX focal-plane detector.

Speaker: Dr Thuthukile Khumalo (NRF-iThemba LABS)

177 Electromagnetic Properties of the 106Cd Nucleus and Experimental Validation of the Generalized Brink-Axel Hypothesis (gBA)

This study extracts new experimental γ-ray strength function (γSF) and nuclear level density (NLD) data for the ¹⁰⁶Cd isotope using the newly developed Shape Method, coupled with the Oslo Method. These methods are applied to particle-γ coincidence data from the ¹⁰⁶Cd(³He, ³He'γ)¹⁰⁶Cd reaction at the Cyclotron Laboratory of Oslo University (OCL). The functional forms of the γSF and NLD have been normalized using the Shape Method, which enables the extraction of γSF and NLD data even in the absence of experimental neutron resonance spacing. This experimental data is then used to calculate the ¹⁰⁶Cd(n, γ) cross-sections within the Hauser-Feshbach formalism. Moreover, this study experimentally tests the validity of the generalized Brink-Axel hypothesis (gBA) in the mass region A=106 for the first time, which asserts that the γ-ray strength function (γSF) is independent of excitation energy. Additionally, we extend our investigation to ¹⁴⁰La, where the validity of the gBA is tested experimentally using data from the ¹³⁹La(d,p) reaction, also conducted at OCL. Finally, the thermodynamic properties of ¹⁰⁶Cd nucleus are extracted for the first time. Details of our findings will be presented at the upcoming conference.

Speaker: Ms Ayabulela Tsewu (University of Johannesburg)

178 Theoretical studies of chiral systems described within particle-rotor model

Chirality in nuclear systems requires an aplanar orientation of the total angular momentum and stable triaxial nuclear shape is needed [1-2]. It is expected that the angular momenta of an odd particle and an odd hole (both occupying high-j orbitals) are aligned predominantly along the short and the long axes of the nucleus respectively, whereas the collective rotation occurs predominantly around the intermediate axis of a triaxially deformed nucleus to minimize the total energy of the system. Experimentally one observes ∆I = 1 rotational partner bands built on two- or multi-quasiparticle configuration. Multiple chiral bands (MχD) with different or same nucleon configuration can indeed form in a single nucleus, as theoretical calculations show (e.g., 3-5]), and experimental data suggest (e.g., [6-8]).
Investigations using the particle-rotor model have shown that the fingerprints of chirality in the two-quasiparticle system can occur in an idealised model description, where an odd proton and an odd neutron are restricted to one orbital each located at the lowest- and highest-energy orbitals or vice versa of a high-j shells [9-10]. For systems with many-quasiparticles, the calculations showed that nuclear chirality can also persist [11-13].
The present work reports on the review of theoretical studies of chiral systems performed using two-quasiparticle-rotor [14] and many-particle-rotor [15] models in different mass regions.

[1] S. Frauendorf, J. Meng, Nucl. Phys. A617, 131 (1997)
[2] S. Frauendorf, Rev. Mod. Phys. 73, 463 (2001).
[3] T. Koike et al., Phys. Rev. C 67, 044319 (2003).
[4] S. Wang, et al., Phys. Rev. C 74, 017302 (2006).
[5] B. Qi et al., Phys. Rev. C 98, 014305 (2018).
[6] T. Roy et al., Phys. Lett. B 782, 768 (2018).
[7] C. M. Petrache, et al., Phys. Rev. C 97, 041304(R) (2018).
[8] C. Liu, et al., Phys. Rev. Lett. 116, 112501 (2016).
[9] E. A. Lawrie and O. Shirinda, Phys. Lett. B 689(2-3), 66 (2010).
[10] O. Shirinda and E. A. Lawrie, Eur. Phys. J. A 48(9), 118 (2012).
[11] O. Shirinda, E. A. Lawrie, and B. G. Carlsson, Acta Phys. Pol. B 44(3), 341 (2013).
[12] O. Shirinda and E. A. Lawrie, Eur. Phys. J. A 52(11), 344 (2016).
[13] O. Shirinda and E. A. Lawrie, Acta Phys. Pol. B Proc. Suppl. 11(1), 149 (2018)
[14] P.B. Semmes and I. Ragnarsson, AIP Conf. Proc. No. 259, p.566 (1992)
[15] B.G. Carlsson and I. Ragnarsson, Phys. Rev. C74, 044310 (2006).

Speaker: Dr Obed Shirinda (Sol Plaatje University)

179 Systematics review of low-lying positive parity structures in the 160 mass region.

For decades now, the low-lying first excited 0+ bands have been attributed to “β -vibrations”, following the seminal works of Bohr and Mottelson [1, 2]. Recent discoveries have demonstrated that these bands could arise due to other modes excitations, such as quadrupole pairing [3] and shape-coexistence [4].

The current work performs a systematics review of low-lying structures in the 160 mass region. In particular, this work focus on the structural behaviour of bands built on the first excited 0+ and 2+ bands, which are traditionally understood as β and γ bands, respectively. The results of the systematic review are presented and the implications of the findings are there from discussed.

Reference

[1] A. Bohr, Mat. Fys. Medd. Dan. Vid. Selsk. 26, 14 (1952).
[2] A. Bohr and B. R. Mottelson, Mat. Fys. Medd. Dan. Vid. Selsk. 27, 16 (1953).
[3] J.F. Sharpey-Schafer et al., European Physical Journal A (2019)55:15
[4] K. Heyde and J. L. Wood, Reviews of Modern Physics 83, 1467 (2011).
[5] P.E. Garrett, J Phys. G: Nucl. Part. Phys. 27, R1 (2001).

Speaker: Siyabonga Majola (University of Johannesburg)

180 Exciting the Hoyle state in 12C selectively populated using the 10B(6Li,4He)12C reaction

An excited state in 12C close to the 3-alpha breakup was predicted by Fred Hoyle in 1954 and was identified in 1962 by Cook et al. as the 0+ state lying at an excitation energy of 7.65 MeV. It was the key to understanding the production of 12C and heavier elements in the Sun (stars) up to iron. In the Sun’s core, fusion of two alpha-particles leads to the production of excited 8Be and then the capture of another alpha-particle a + 8Be produces excited 12C close to the Hoyle state. Subsequently, gamma-decay from the Hoyle state to the 4+ (4.43 MeV) state and down to the 12C ground state 0+ (0.0 MeV) results in the production of stable 12C, as opposed to 3-alpha breakup. However, the observed enhanced 12C production rate in stars is speculated to be achieved through excited states of the Hoyle state. The existence of broad excited Hoyle states at 12C(2+, 9.8 MeV) and 12C*(4+, 13.3 MeV) have been reported, previously not identified because of other nearby strongly excited states in 12C.

The 10B(6Li,a)12C* reaction selectively excites 2+ states in 12C and because of the high Q-value of Q = +24.6 MeV the high energy alpha-particles are easily identified with good energy resolution. Measurements were taken at the EN Tandem Van de Graaff accelerator of iThemba LABS (Gauteng) using 6Li beams at E_Lab = 20 MeV incident on thin 10B targets. Results will be presented for the observed high energy alpha-particles corresponding to states excited in 12C up to and above the Hoyle state. In addition, preliminary results will be shown for coincidence measurements between the outgoing high energy alpha-particle and the 12C reaction partner.

Speaker: Prof. John Carter (University of the Witwatersrand)

Nuclear, Particle and Radiation Physics-2

181 Measurement of the top quark Yukawa coupling from tt kinematic distributions in the dilepton final state

An extraction of the top quark Yukawa coupling ($Y_{t}$) from top quark pair production is presented using proton-proton collisions at $\sqrt{s} = $ 13 TeV, corresponding to an integrated luminosity of 140 $fb^{-1}$, recorded by the ATLAS experiment. Corrections from a Higgs boson exchange between the top quark and top anti-quark can produce non-negligible modifications to differential distributions near the energy threshold of $t\bar{t}$ production. The kinematic distributions sensitive to these modifications at parton level, are the invariant mass of the $t\bar{t}$ system (m$_{tt}$) and the azimuthal angle of the top quark with respect to the beamline in the rest frame of the $t\bar{t}$ system known as $\cos (\theta^*)$ This analysis aims to constrain $Y_{t}$ indirectly using the kinematic distributions of $t\bar{t}$ pair events using the e$\mu$ dilepton final state.

Since we are working in the dilepton channel $t\bar{t}$ $\rightarrow$W$^+$bW$^-$b $\rightarrow \ell^+\nu b\ell^-\nu b$. The ATLAS experiment cannot measure the neutrinos and as such we need to reconstruct the $t\bar{t}$ kinematics sensitive to variations in $Y_{t}$. Machine learning was used to reconstruct the mass of the top quark system as this provides the greatest sensitivity to variations in $Y_{t}$. A binned profile likelihood fit was then implemented to extract a blinded estimation of $Y_{t}$ using Asimov data including a complete set of statistical and systematic uncertainties.

Speaker: Cameron Garvey (University of Cape Town)

182 A search for tWZ production in the ATLAS experiment Run 2 dataset

The $tWZ$ production is a rare and unobserved Standard Model process which refers to the production of a single top quark with an associated W boson and Z boson. The $tWZ$ process is sensitive to top-electroweak couplings and thus it will be an important input into global Standard Model Effective Field Theory (SMEFT) fits. Additionally, this process can be used as a background in other top process such as $ttZ$ cross section measurements. A search for $tWZ$ production was performed using $140\text{fb}^{-1}$ proton-proton collision data at center of mass energy of $\sqrt{s} = 13$TeV measured with the ATLAS detector at CERN. This search will focus on 4 lepton final states (electrons and muons). The analysis has been re-implemented on Release 25 and on latest ATLAS recommended analysis frameworks, TopCPToolKit and FastFrames. The signal regions (SRs) and control regions (CRs) were defined based on multiplicities of physics objects such as the number of jets, number of b-tagged jets, number of Z boson candidates, etc. A deep neural network is used to discriminate signal and background. The signal parton shower systematic uncertainty will be evaluated for the first time. The expected signal strength of $tWZ$ production $\mu_{tWZ}$, will be extracted using a blinded maximum-likehood fit to multiple SRs and CRs with full systematic uncertainties.

Speaker: Thobani Sangweni (University of Cape Town)

183 Exploring toponium formation at the LHC

The top quark, the heaviest known elementary particle ($m_t \approx 172.52\,$GeV), plays a crucial role in probing the Standard Model (SM) at high energies. At the Large Hadron Collider (LHC), top quark pair production ($t\bar{t}$) is the dominant mechanism for top production. The top quark predominantly decays to a $b$-quark and a $W^+$ boson, the latter of which decays either leptonically or hadronically. The dileptonic decay channel ($pp \to t\bar{t} \to b \bar{b} W^+ W^{-} \to b \bar{b} l^+ \nu_{l} l^{-} \bar{\nu}_{l}$, with $l = e, \mu$) provides a clean and sensitive probe of the near-threshold region of $t\bar{t}$ production, where the center-of-mass energy is just sufficient to produce the top pair. This threshold region is especially sensitive to key SM parameters such as the top mass, width, and Yukawa coupling. It also offers a unique opportunity to explore the formation of toponium, a relatively unexplored bound state of a top and anti-top quark. Earlier studies indicated discrepancies between theoretical predictions and experimental data in this region, partly due to the absence of toponium effects in standard perturbative calculations. We present an updated and comprehensive study of toponium-induced corrections to various kinematic distributions, including $m_{t\bar{t}}$ and $\Delta \phi(l \bar{l})$ at next-to-next-to-leading order (NNLO) in QCD. Additionally, we incorporate toponium corrections into 2-D differential observables such as $|\Delta \phi^{e\mu}|:m^{e\mu}$, at next-to-leading order (NLO). This analysis compares the improved predictions, now incorporating toponium effects, to LHC data and includes a systematic assessment of theoretical uncertainties.

Speaker: Aminul Hossain (University of Cape Town)

Photonics: Photosynthesis & Biophysics

Convener: Saturnin Ombinda-Lemboumba (Council for Scientific and Industrial Research (CSIR),)

184 Light-harvesting protein aggregation studied by real-time feedback-driven single-particle tracking spectroscopy.

Single-molecule spectroscopy (SMS) has significantly advanced our understanding of the properties and dynamics of biomolecules. However, the environment used in SMS experiments is a poor representation of the natural cellular environment, and therefore the results of these studies may be of limited physiological relevance. One limitation of conventional SMS experiments is the need to immobilise the particles via surface attachment. This limitation is overcome by real-time feedback-driven single-particle tracking (RT-FD-SPT), a technique that allows spectroscopic measurements on individual, freely diffusing particles, with the added benefit of diffusion information. We employed RT-FD-SPT to study the aggregation of plant light-harvesting complex II (LHCII). Such aggregation is thought to be related to non-photochemical quenching (NPQ), an important photoprotective process. We combined spectroscopic and diffusion information to disentangle the interplay of aggregate size, detergent concentration, fluorescence intensity and lifetime, variables that are often overlooked in ensemble experiments.

Speaker: Bertus van Heerden (University of Pretoria)

185 Temperature-dependent single-molecule spectroscopy of plant protein aggregates

Plants live with a continuous paradox: while light is the lifeblood for their growth, too much light can be extremely harmful. Their photosynthetic machinery, therefore, regulates the amount of absorbed energy in a photoprotective process known as non-photochemical quenching (NPQ). Aggregation of the main light-harvesting complex of plants, LHCII, is considered an excellent model system for the major component of NPQ. We performed a temperature-dependent (down to 4 K) single-molecule spectroscopy study of two types of LHCII aggregates to resolve their spectroscopic heterogeneity. We discovered that exciton annihilation is severely underestimated in steady-state bulk studies of LHCII aggregates and explains the varying spectral shapes in different time-resolved bulk studies.

Speaker: Prof. Tjaart Krüger (University of Pretoria)

186 Increased exciton annihilation in incrementally aggregated photosynthetic antenna complexes from plants

The automatic photoprotective mechanisms of photosynthetic antenna complexes that initiate light-harvesting have been a subject of great interest for potentially improved solar energy technology, enhanced crop efficiencies, and biosensing. Light-Harvesting Complex II (LHCII) is the main pigment-protein antenna in green plants and exhibits the remarkable capability to switch between a light-harvesting and a photoprotective state when exposed to fluctuating sunlight intensities. The in-vivo conditions that activate this switch can be mimicked by aggregation of LHCII. Despite more than three decades of research, the molecular mechanism responsible for the strong energy quenching in these aggregates is still unknown. We investigated LHCII aggregation in a stepwise manner and performed fluorescence correlation spectroscopy (FCS) along with time-correlated single-photon counting (TCSPC) on a home-built experimental setup to correlate the aggregate composition with their excited-state lifetimes. We discovered a non-linear relationship between the steady-state intensities and average lifetimes, which is explained well by increased annihilation of diffusing singlet excitons due to an accumulation of triplet excitons in aggregates. An approximated model of this singlet-triplet annihilation showed excellent correspondence with the experimental data. These results demonstrate the importance of distinguishing non-linear exciton annihilation from exciton quenching in photoprotective studies of plants.

Speaker: Mr Francois Conradie (University of Pretoria)

Physics for Development, Education and Outreach: Physics in Industry Day

Physics of Condensed Matter and Materials

Theoretical and Computational Physics: Session 8

Convener: Sam van Leuven (University of the Witwatersrand)

187 Adiabatic elimination approach to the completely positive master equation for open quantum Brownian motion

Recently, Bauer et al. [1,2] introduced open quantum Brownian motion (OQBM) as a scaling limit of discrete-time open quantum walks [3,4], providing a new mathematical framework for quantum Brownian motion. In this setting, the dynamics of the Brownian particle are governed by dissipative interactions with a thermal bath and depend on the state of internal degrees of freedom. A microscopic derivation of OQBM for a free Brownian particle subject to decoherent interaction with a thermal environment was subsequently proposed [5,6]. In our recent work [7], we extended this framework by deriving OQBM in a generic dissipative scenario using the method of adiabatic elimination of fast variables. However, this approach led to a master equation that is not completely positive, consistent with the limitations of the standard Caldeira-Leggett model [8,9]. To resolve the issue of positivity, we now apply the rotating wave approximation (RWA) to the system-bath interaction Hamiltonian. This leads to a completely positive master equation for OQBM in the case of a weakly driven open Brownian particle confined within a quadratic potential and dissipatively coupled to a thermal bath. From the resulting dynamics, we derive equations for the first, second, and third cumulants of the position distribution of the OQBM walker.

[1] M. Bauer, D. Bernard, and A. Tilloy, 2013 Phys. Rev. A 88, 062340.
[2] M. Bauer, D. Bernard, and A. Tilloy, 2014 J. Stat. Mech. P09001.
[3] S. Attal, F. Petruccione, C. Sabot, and I. Sinayskiy, 2012 J. Stat. Phys. 147, 832.
[4] S. Attal, F. Petruccione, and I. Sinayskiy, 2012 Phys. Rev. A 376, 1545.
[5] I. Sinayskiy, and F. Petruccione, 2015 Phys. Scr. T 165, 014017.
[6] I. Sinayskiy, and F. Petruccione, 2017 Fortschr. Phys. 65, 1600063.
[7] A. Zungu, I. Sinaykiy, and F. Petruccione, 2025 arXiv:2503.10379.
[8] A. Caldeira and A. Leggett, 1983 Phys. A 121, 587.
[9] A. Caldeira and A. Leggett, 1983 Ann. Phys. (NY) 149, 374.

Speaker: Mr Ayanda Zungu (Centre for Space Research, North-West University, Mahikeng 2745, South Africa)

188 Advancing Thermal Field Theory: NLO Calculations for Finite Size Systems

Understanding the behavior of matter under extreme conditions is one of the key goals of high-energy physics. In particular, the study of the quark-gluon plasma (QGP) offers insights into the early universe and the dynamics of strongly interacting matter. A powerful way to study such systems in thermal equilibrium is through the thermal partition function, which encodes the statistical properties of a quantum field theory at finite temperature. This formalism is often called Thermal Field Theory, and it will be the topic of my talk. Specifically, I would discuss the next-to-leading order finite-size corrections to the partition function in $\phi^4$ theory.

In order to compute the partition function from first principles, we begin in the Hamiltonian operator formalism and move toward a path integral representation. A crucial step in this transition involves coherent states, which form a natural basis for extracting information about quantum fields. These states are particularly useful when computing the trace in the partition function, as they allow us to capture the field configurations involved in the system’s dynamics. Their algebraic properties, particularly the eigenstate property of the annihilation operators, make them especially effective for deriving the path integral in a controlled way.

$Z=Tr[e^{-\beta H}] = \int D\phi \ e^{-\frac{1}{2}\int_0^\beta d\tau \int d^n\mathbf{x} \left[\dot{\phi}^2+\left(\mathbf{\nabla}\phi\right)^2+m^2\phi^2\right]}$

Working in imaginary time and employing periodic boundary conditions in the temporal direction naturally leads to the Matsubara formalism. This framework allows us to express field configurations as discrete Fourier series in terms of Matsubara frequencies. Once this setup is in place, the path integral can be explicitly computed in the free theory, yielding a compact and elegant form of the partition function from which thermodynamic quantities such as the free energy and the pressure can be extracted.

$Z = C\frac{T}{m}\prod'_m \frac{\omega^2_{\ell}}{\left(\omega^2_{\ell} + E^2_\mathbf{p_m}\right)}$

$f = \frac{F}{V} = -\frac{T}{V}\ln{Z}, \qquad P = \frac{\partial(T\ln{Z})}{\partial V}$.

We then consider the extension to interacting theories, where the presence of interaction terms complicates the structure of the path integral and the use of coherent states as a bridge from operators to classical field configurations. The coherent state techniques must be treated with care, especially since time evolution is now governed by the full Hamiltonian and not just the free part. The interaction picture becomes essential, but its use in imaginary time raises subtle issues, particularly in how time ordering and commutators behave in the thermal trace. These complications are closely related to the need for more sophisticated contour prescriptions in the complex time plane. The appropriate prescription is the Schwinger-Keldysh contour, which is necessary when studying real-time dynamics in combination with thermal processes.

Through this careful computation, we have found additional correction terms to the path integral representation of the partition function that do not appear in existing literature. As a preview, we show the current result of the discretized finite path integral interacting partition function including these corrections:

$Z = \int D\phi \ e^{-\frac{1}{2}\int_0^\beta d\tau \int d^n\mathbf{x} \left[\dot{\phi}^2+\left(\mathbf{\nabla}\phi\right)^2+(m^2+\frac{\lambda}{4!}\langle 0|\hat{\phi}^2|0\rangle)\phi^2+\frac{\lambda}{4!}\phi^4+\frac{\lambda}{4!}\langle 0|\hat{\phi}^4|0\rangle\right]}$

The precise interpretation of these corrections is still under investigation, but they may have important implications for how interacting thermal systems are treated beyond the leading order. By the time of the conference, I expect to have resolved the origin of these terms and to have explicitly evaluated the path integral for the fully interacting theory. I may already be able to present preliminary results on the renormalized computation of next-to-leading order finite-size corrections to the pressure.

Speaker: Rens Roosenstein (University of Cape Town, University of Amsterdam)

189 Superconformal indices in closed form

Superconformal indices are a type of partition function that encode the protected spectrum of a superconformal field theory (SCFT). They are invariant under continuous deformations and renormalization-group flows, and provide insights into physical and mathematical equivalences between dual SCFTs and their low energy dynamics. In this talk, I will explain the background and motivation for calculating superconformal indices, present the results of our computation of well-defined closed form expressions for the full Superconformal Index, and its supersymmetric limits, namely the Hall-Littlewood, Schur and Macdonald indices in the cases of $\mathcal{N}=1$, $\mathcal{N}=2$, and $\mathcal{N}=4$ SCFTs. Lastly, I will conclude with a review of their physical interpretation of our results.

Speaker: Kayleigh Mathieson (University of the Witwatersrand)

10:20 AM Morning Tea

Applied Physics

Convener: Marco Mariola

190 Measurement of fundamental ion-atom interaction parameters for heavy ion beam materials analysis

The interaction of high-speed ions with target atoms in solid matter continues to be of both fundamental and practical interest. In materials research and development, one of the key ion-atom interactions of interest is the energy loss of the incident ion to target nuclei and the electron cloud. Accurate theoretical description of ion energy loss processes in matter is key to the development of ion beam analytical and materials synthesis/modification techniques. Rutherford Backscattering Spectrometry (RBS), Elastic Recoil Detection Analysis (ERDA and Particle Induced X-ray Emission (PIXE) spectroscopy are now well-stablished ion beam analysis (IBA) techniques in materials research. For IBA using light ions (Z = 1, 2) existing theoretical models for the energy loss per unit depth (i.e. stopping force) for RBS, ERDA, and X-ray production cross section for PIXE fare quite well in the range of beam energies used in analysis. Recent developments in IBA are geared towards using heavy ions (Z>6) for analyses. This, however, has come with analytical challenges in that the predictive accuracy of existing theories and models for both stopping force and X-ray production cross sections is largely inadequate for heavy ion IBA work. There is a therefore a continual need for experimental data to aid further development and validation of theory. This presentation describes the contribution made by our group to the global databases of stopping force and X-ray production cross section data for applications in heavy ion beam analytical techniques

Speaker: Mandla Msimanga (Tshwane University of Technology)

191 Nanocrystal Enhancement of Low-Cost Scintillators for PET Imaging Application

Positron emission tomography (PET) is a valuable medical imaging technique widely used in the early diagnosis of cancer, as well as in the assessment of cardiovascular, neurological, and metabolic disorders. PET scanners detect pairs of 511 keV gamma rays emitted via the annihilation of positrons from a radioactive tracer injected into the patient. The industry standard detectors used in these systems are typically made from monolithic crystal scintillators, which are costly and contribute significantly to the overall expense of PET scanner production. This greatly restricts access to PET scanners to populations in Africa and the Middle East. Alternative scintillators, such as ceramics and plastics, offer cost advantages but are currently limited by their low light yield, slow scintillation response times, and minimal stopping power at the required energies. In this study, we aim to enhance the scintillation properties of such low-cost scintillators by suspending high-Z nanocrystals in the matrix. This approach aims to combine the favorable characteristics of ceramics and plastics, offering a potential route to affordable and efficient PET detectors suitable for resource-limited settings. To this end, we suspended CdS nanocrystals fabricated by our collaborators at the University of Zululand in epoxy-resin pixels at concentrations ranging from 0.05% to 0.6%, which we characterised at CERN. Standard optical characterisation revealed a red-shift in the emission spectrum with increasing nanocrystal concentration, accompanied by greater light absorption. Scintillation decay times were measured using a time-correlated single photon counting (TCSPC) technique under soft (0–40 keV) pulsed x-ray excitation in reflection mode.

Speaker: Declan Mahony (University of Cape Town)

192 Preliminary Investigation of the Mechanical Properties of Tissue Biopsies

Cancer induction and progression have been significant challenges that face humanity. Several procedures and methods have been used to detect the different stages within the clinical setting. However, many of these clinical tests are geared towards biochemical cues. This study studied the inherent nanomechanical properties of two breast and colorectal biopsies. The tissues were obtained from a biobank and then stored in 10 % formalin for onward transportation to the laboratory. A slice from the tissue samples was cut out, attached to a disc, and placed inside a Cypher VRS atomic force microscope. The tissue was then hydrated with phosphate buffer saline. The indentation curves of the samples were then acquired. The indentation curves were then fit into the Hertz model to extract the mechanical properties needed. The range of Young’s modulus obtained for the colorectal normal biopsies was between 2.174±0.299 and 35.005±5.025 MPa, while the values obtained for the cancer biopsies range between 0.524±0.017 and 5.120±0.218 MPa. However, the range obtained for the normal breast biopsies was 113.319±7.770 and 140.202±11.696 kPa, while the range of Young’s modulus obtained for the cancer breast tissues was between 1.009±0.040 and 4.038±0.282 kPa. The study concluded that there is a significant difference in the indentation measurements between cancer tissues, and these differences also vary with the tissues.

Speaker: Kayode Dada (University of Johannesburg)

193 Advancing solar energy research with perovskite materials

Perovskite materials used for solar cell, demonstrated remarkable PCE, that increased from 3.8% in 2009 to approximately 19.44% in 2019. However, challenges such as stability and scalability remain significant obstacles to commercialization. Improvement of the perovskite solar cell stability includes material composition and crystal quality, using both intrinsic and extrinsic methods. Researchers have reported that utilizing strategies like multi-cations, multi-halides, doping, altering crystal structure and incorporating chalcogenides have improved PCE. In addition, extrinsic methods such as encapsulation, interfacial engineering and buffer layers have been used to improve stability of perovskite materials system. Furthermore, engineering solar cell systems, which include Si-tandems are reported to be capable of improving both stability and scalability. This paper will present the results from published work towards achieving stability of perovskite solar cell.

Speaker: Mmantsae Diale (University of Preoria)

194 An empirical method to negate Bragg-peak shifts due to partial gauge volume illumination in neutron powder diffraction studies

Partially filled neutron gauge volumes in neutron powder diffraction experiments lead to anomalous shifts in diffraction peak positions. In stress analyses, these shifts create systematic errors in lattice parameter measurements, potentially leading to incorrect interpretations of strain if left uncorrected. This phenomenon is known as the pseudo-strain effect.

The instrumental gauge volume (IGV) refers to the region which is defined by the intersection of the incident and diffracted neutron beam paths. When this volume is fully embedded in a homogenous sample that does not exhibit large grains or preferred crystallographic orientation, the geometric centre of the IGV closely corresponds to the neutron-weighted centre of gravity (NCOG) of the crystallites being probed. The NCOG represents the effective spatial position within the sample from which the diffracted neutron intensity appears to originate and is influenced by the incident beam intensity distribution, sample geometry, relative sample position / orientation and attenuation cross-sections. In situations where the sample is smaller than the beam, or the beam is not fully embedded in the sample, offsets may exist between the IGV centroid and the NCOG.

To account for the effects of partial illumination, a method was devised to determine the NCOG offsets considering the factors mentioned based on previous investigations [1]. In addition, an empirical model, shown in Figure 1, was devised to correct the peak shift due to the combined effect of NCOG offsets and the non-negligible wavelength distribution spread of the incident neutron beam.

Figure 1. (a) Experimental setup and (b) d-spacing shift due to positional changes of the NCOG within the IGV

[1] D. Marais, Z.N. Sentsho, A.M. Venter. Numerical neutron attenuation correction for partially-illuminated powder samples. Materials Characterization. 153(2019)234-239 (https://doi.org/10.1016/j.matchar.2019.05.011.)

Speaker: Dr Deon Marais (South African Nuclear Energy Corporation (Necsa) SOC Ltd.)

Astrophysics & Space Science: Dark matter and instrumentation

195 Probing the pi-axiverse with astrophysics

With the WIMP parameter space slowly being ruled out by experiments on all fronts, axions have become a highly studied alternative dark matter candidate. In this talk we present a particle physics model where the pion states of a dark copy of QCD have both axion and dilaton phenomenologies. This model allows for the formation of dilute axion stars over a far larger parameter space than allowed in typical axion models. We explore whether such a model could be detected via FRB-like emissions associated with stable axion star mergers, these have unique broad spectra (rather than axion lines). We demonstrate that strong detection prospects exist for these events with both MeerKAT and upcoming experiments like the SKA and ngVLA.

Speaker: Geoff Beck (University of the Witwatersrand)

196 In Search of Dark Matter with MeerKAT Radio Telescope in Dwarf Spheroidal Galaxies

MeerKAT's combination of high-sensitivity and angular resolution makes it a particularly well suited radio interferometer for detecting faint cosmic radio emissions that would otherwise remain inaccessible by other instruments.
This capability is especially important in identifying weak, diffuse radio signals that could be associated with dark matter interactions.

Our research focuses on searching for dark matter signals from dwarf spheroidal galaxies (dSphs), which are promising targets due to their high mass to light ratios, well characterized stellar kinematics and established dark matter density.

We present results from MeerKAT observations of the Milky Way satellite Reticulum II.
We aim to constrain the dark matter parameter space-particularly the Weakly Interacting Massive Particles (WIMPs), by analyzing potential radio signals resulting from their annihilation or decay.
This involves probing two key parameters: the particle mass and the annihilation cross section.
If no significant signal is detected, we set upper limits on these parameters, helping to rule out theoretical models that predict stronger signals than observed.
As sensitivity improves, more theoretical models can be excluded, refining the landscape for future dark matter searches.

Speaker: Shibre Semane (University of the Witwatersrand)

197 Dark Matter in Centaurus: an investigation with MeerKAT

Modern radio interferometers, with their exceptional sensitivity and angular resolution, are uniquely suited to detect the faint signatures predicted from Weakly Interacting Massive Particles (WIMPs). Among the most powerful instruments in the southern hemisphere is MeerKAT, a precursor to the Square Kilometre Array (SKA), which provides unparalleled capabilities for exploring dark matter through radio observations.

In this study, we analyze data from the MeerKAT Galaxy Cluster Legacy Survey to examine galaxy clusters as prime targets for WIMP detection. By combining state-of-the-art dark matter modeling with advanced radio astronomy techniques, we probe the WIMP parameter space and derive competitive upper limits on the annihilation cross-section across more than three orders of magnitude. These results mark a substantial improvement in the field, offering new perspectives on dark matter searches in galaxy clusters.

We present our results for the Centaurus cluster, a nearby, massive, and relaxed cool-core system with a prominent brightest cluster galaxy (BCG). Additionally, we discuss the challenges of comparing theoretical WIMP-induced radio emissions with observed cluster fluxes, emphasizing the critical distinction between methodologies that utilize processed images and those that require raw visibility data. This consideration will grow increasingly important as next-generation facilities like the SKA generate vast data volumes, necessitating more efficient computational strategies for analysis and interpretation.

Speaker: Natasha Lavis (Centre for Astrophysics, University of the Witwatersrand)

198 Characterisation and Calibration of the Kepler KL4040 sCMOS camera for Optical Observations at the UFS/Boyden Observatory

The Kepler KL4040 sCMOS camera by Finger Lakes Instruments was evaluated for its suitability as an affordable alternative to older CCD sensors for optical photometry at the Boyden Observatory. Due to the sensor architecture where each pixel has its own electron to voltage converter, a thorough characterisation and calibration study was conducted to identify key performance factors and necessary considerations for operational implementation. The KL4040 achieves a high dynamic range by merging two 12-bit images into a single 16-bit image, with binning performed via software.
Laboratory tests examined bias stability, dark current, and photo-response characteristics. Bias frames exhibited a 7.5% increase in mean counts as temperature rose from -15°C to 10°C, with dark current showing a linear temperature dependence. A small offset between the merged images for the 12bit to 16bit conversion was identified but was correctable through adjustments to the gain transition parameter that determines the offset value between high and low gain. Photo-response curves for the B, V, R, and I bands confirmed linearity across all bands. Fixed pattern noise (FPN), a known issue in sCMOS sensors, was effectively mitigated through bias, dark, and flat-field corrections.
On-sky tests included standard field photometry of the AAVSO SA107 field. Transformation coefficients enabled photometric corrections to within 2% of known values. Additionally, high cadence photometry of the pulsating white dwarf binary system AR Sco was performed to test fast photometry throughput. A full orbital period of AR Sco was captured at a 6 s cadence, revealing the 118.2 s beat period via Lomb-Scargle analysis. The folded light curve displayed clear periodic variations.
These results confirm the KL4040 as a viable, cost-effective alternative to CCDs for photometry at the Boyden Observatory. While it lacks single-photon sensitivity, its quantum efficiency, fast readout, and large sensor size make it a strong contender for astronomical imaging on a budget. In addition, because of image manipulation such as binning and sub-frame selection happening post image readout and is not hardware based, image quality, size and throughput can be optimized through software development and is not limited to hardware capabilities.

Speaker: Dr Hendrik Jacobus van Heerden (University of the Free State)

199 Wits Astronomical Plate Archive – preservation of a century of Southern Hemisphere astronomy at the Johannesburg Observatory

The trend worldwide is to preserve astronomical photographic plates by digitisation, with some plates dating back to over a century. Indeed, South Africa should be no exception and has a long tradition of observing the night sky of the Southern Hemisphere, initially to produce star charts for improved navigation by seafaring ships. This gave way to observatories for mapping star positions precisely by using telescopes to record images on photographic plates. The John Franklin-Adams wide-angle telescope, donated in 1909, was originally sited at the Union Observatory (present-day Johannesburg Observatory, Johannesburg) and was later moved to the Observatory’s Dark Sky Outstation at Toppieshoek, Hartbeespoort. Here, it was joined by the Rockefeller 16” Twin Astrograph in 1938, constituting the Netherlands Leiden Observatory Southern Station. In particular, observations were made for variable stars, binaries and transients. It should be noted that from 1911 to 1970 the Franklin-Adams telescope was used in the discovery of 148 asteroids and the production of a set of 556 sky maps south of -19 degrees.

In total the Franklin-Adams telescope produced over ten thousand, monochrome, photographic plates, up to a size of 15” x 15”. This heritage is not conveniently accessible and, in addition, the emulsion of such plates deteriorates over time. By taking high-resolution digital photographs of the plates, the plate information is preserved and becomes easily accessible using modern computers and networks.

This presentation follows the steps for setting up the Wits Astronomical Plate Archive in 2015 in order to preserve the Franklin-Adams plates and digitise the images for future long time-based astronomical use. Also, attention is paid to the heritage value of the Franklin-Adams and Rockefeller telescopes, championed by the Magaliesberg Association for Culture and Heritage (MACH).

Speaker: Prof. John Carter (University of the Witwatersrand)

Nuclear, Particle and Radiation Physics-1

Nuclear, Particle and Radiation Physics-2

200 Dark photons search with the ATLAS detector at the LHC

Many extensions to the Standard Model (SM) introduce a hidden or a dark sector rising from an additional $U(1)_d$ gauge symmetry, to provide candidates for dark matter in the universe and a possible explanation to astrophysical observations such as the positron excess observed in the cosmic radiation flux. The gauge boson of the dark sector would be either a massless or a massive dark photon that can either kinetically mix with the SM photon, or couple to the Higgs sector via some mediators. If dark photons decay back to the SM particles with a significant branching ratio, we could either observe measurable deviations in some Higgs decay channels or new exotic signatures that would be accessible at the LHC energies. An overview of current results on dark photon searches with the ATLAS detector will be presented, targeting a wide range final states using different data analysis techniques. Finally, new ideas for dark photon searches using Run 3 data and their current status will be discussed.

Speaker: Rachid Mazini (School of Physics, The University of the Witwatersrand)

201 Search for Higgs decaying to invisible particles via vector boson fusion with ATLAS

Given the discovery of the Standard Model Higgs boson in 2012 by both ATLAS and CMS experiments at the Large Hardon Collider at CERN, further properties of the Higgs boson are important to be explored. The search for Higgs decaying to invisible particles is a potential portal to look for physics beyond the Standard Model. Among all Higgs production channels at the LHC, vector boson fusion provides the most sensitivity for the concerned process. Direct search for vector boson fusion production of the Higgs boson decaying invisibly using 139 fb-1 at 13 TeV centre-of-mass energy at ATLAS will be presented. Further development for the similar search at Run 3 with discussion about the interpretation will also be shown.

Speaker: Ms Loan Truong (University Of Johannesburg)

202 Search for a new spin-0 scalar and a spin-1 boson using Run2 ATLAS detector data

We present a search for a spin-1 boson together with a spin-0 scalar wherer the additional scalar decays into a four lepton final state $(\ell = \mu$~or $e )$ via two intermediate dark vector bosons in the folllowing decay channel $S \rightarrow Z_d Z_d \rightarrow 4\ell$. In this scenario, the targeted additional scalar ($S$) mass ranges is between 20 GeV and 1 TeV where we exclude the Higgs boson mass window of $115~GeV < m_S < 130~GeV$ while the dark vector boson has a mass between 15 and 300 GeV. The search is conducted using $p-p$ collison data collected using the ATLAS detector at the LHC which corresponds to a center of mass energy of $\sqrt{S} = 13 TeV$ and an integrated luminosity of 139 $fb^{-1}$. There were no significant excesses observed. Therefore, a 95\% upper limit was set on the cross-section $\times$ branching ratio as a function of the mass of both particles $m_S$ and $m_{Z_d}$.

Speaker: Xola Mapekula (University of Johannesburg)

203 The W boson as a probe for the initial state of hadron collisions at the LHC

The charged vector boson (W$^\pm$) is produced in the hard partonic scattering of relativistic hadronic collisions, where its production cross-section can be calculated theoretically from perturbation theory and the relevant hadronic parton distribution functions (PDFs). Since it does not interact strongly and decays leptonically, the W boson serves as an ideal probe of the initial state of the collision - such as the contributing quark PDFs. In this presentation, the focus will be on the production of W$^\pm$ in the forward rapidity region of simulated relativistic proton-proton collisions, where the POWHEG and Pythia event generators are used to simulate the events of interest. The W$^\pm$ production is studied via the muonic decay channel as W$^+\rightarrow\mu^+\nu_\mu$ and W$^-\rightarrow\mu^-\bar{\nu}_\mu$, where the muon can be measured with the ALICE Muon Spectrometer in the forward rapidity region of $2.5 < y < 4.0$. The primary charged-particle multiplicity is introduced as an additional observable of interest to study the initial state - where the self-normalised W$\rightarrow\mu$ production as a function of the self-normalised multiplicity is defined and studied specifically. It is demonstrated that the study in proton-proton collisions can serve as a meaningful baseline measurement for other hadronic collision systems, where an outlook is presented to do the same study in proton-lead and lead-lead collisions with Run 3 data from ALICE.

Speaker: Stephan Potgieter (University of Cape Town)

Photonics: Photosynthesis & Biophysics

Convener: Saturnin Ombinda-Lemboumba (Council for Scientific and Industrial Research (CSIR),)

204 The efficacy of PAM fluorometry as a tool to quantify heat stress in wheat

Fluorescence (spontaneous emission) is a highly sensitive probe for a multitude of molecular processes during the light-dependent steps of photosynthesis in numerous organisms. In living organisms, the fluorescence signal is dwarfed by reflection and scattering; however, the signal-to-noise ratio can be significantly enhanced by gating the fluorescence to sub-ms excitation pulses through a non-invasive technique known as pulse-amplitude-modulated (PAM) fluorometry. Wheat is an economically important crop that is susceptible to heat stress and consequent yield reduction at temperatures above 30°C. However, the changes to molecular processes that cause the decrease in yield have not been well reported. In this study, PAM fluorometry was used to investigate the effects of high temperatures on the energy transfer pathways during the light-dependent steps of photosynthesis. The quantum efficiency of energy conversion from light to chemical energy was not significantly altered at 30°C but was reduced by 10.7% at 35°C. We show that the biological changes due to the heat shock response can be measured at a time resolution of 30 seconds. PAM fluorometry, and thus fluorescence, is able to provide information about the effects of heat stress on electron transport during light-dependent photosynthesis. This opens many possible directions of study, such as investigating the effects of different types of stress on photosynthesis or further modelling the photosynthetic energy-transfer pathways under heat stress.

Speaker: Ms Sarah Burnett (University of Pretoria)

205 Using a synthesised wavelength to non-locally probe the depth of objects

Quantum ghost imaging (QGI) makes use of a pair of quantum entangled photons whereby one interacts with an object while spatial projective measurements are performed on the other. Using the correlated detections of the entangled photons, the transverse spatial profile of the object can be retrieved. QGI has recently been used to retrieve phase information of a field, however the depth profile of objects with heights which are orders of magnitude larger than the wavelength of the photons could not be achieved. In this presentation we will be learning how to probe an object with two diCerent wavelengths to obtain its depth profile using QGI, the depth profile of the object is not resolvable with either of the wavelengths individually.

Speaker: Neelan Gounden (University of the Witwatersrand)

Physics for Development, Education and Outreach: Physics in Industry Day

Physics of Condensed Matter and Materials

Theoretical and Computational Physics: Session 9

Convener: William Horowitz (University of Cape Town)

206 Advancing Dark-QCD searches: Model Development, Constraints, and Novel Anomaly Detection Technique

Strongly interacting dark sectors, colloquially referred to as dark-QCD, is becoming increasingly popular in the collider community, primarily because of the rich phenomenology and the novel signatures it offers. The author pioneered the first search for semi-visible jets in ATLAS, and is following that up with multiple studies focussing on other final states (arXiv:2207.01885), new generator setups to simulate the signals (WiP), new discriminating observables (arXiv:2209.14964, WiP), setting constraints on these models based on existing results (arXiv:2502.11237) and a novel use of anomaly detection algorithms (WiP) to aid finding these signatures. In the presentation, the lessons learnt from the ATLAS result will be discussed, and these work-in-progress results on model development, constraints of the models, as well anomaly detection method being proposed will be presented, essentially summarising the state-of-the art in the semi-visible jets.

Speaker: Deepak Kar (University of Witwatersrand)

207 Spin chains for N=2 quiver theories

Integrability of gauge theories in the planar limit is a very powerful property which allows for a complete determination of the spectrum of the theory, but so far it has mostly been relevant for the most supersymmetric theory, $\mathcal{N}=4$ super Yang-Mills and we would like to extend this to a much larger class of theories. In this talk, I will focus on $\mathcal{N}=2$ superconformal theories obtained by orbifolding $\mathcal{N}=4$ super Yang-Mills and then marginally deforming by varying the values of the couplings. We have determined the Lagrangians of these theories in terms of factors arising from the representation theory of the discrete groups and deformation parameters. From these Lagrangians, we were able to determine the corresponding dilatation operator for the theories, in terms of the representation theory factors and deformation parameters. It is known that, before marginally deforming, the integrability structure of the N=4 SYM is retained by these theories. Our results are the first step to determining whether or not this structure remains after marginal deformations.

Speaker: Jarryd Bath (University of Pretoria)

208 Computing the SU(N) Shur index for N=4 super Yang-Mills

In this talk, I will discuss a computation of the Schur Index of $\mathcal{N}=4$ super Yang-Mills theory with $\mathrm{SU}(3)$ gauge group. The Schur index counts the number of 1/8 BPS states of a theory. In order to find the gauge invariant (physical) states one must compute several nested complex contour integrals. Through Cauch’s theorem, this reduces to finding the residues of the integrands of these integrals. However, there are an infinite number of these residues. We use the partial ellipticity property of the integrand to find all the residues. This computation is the first step to see if we can find any trends relating the rank of the gauge group to the Schur index. The ultimate goal being able to find the Schur index for $\mathcal{N}=4$ super Yang-Mills with a $\mathrm{SU}(N)$ gauge group, where $N$ is arbitrary.

Speaker: Jarryd Bath (University of Pretoria)

Photonics: Biophotonics & PDT-Cancer Therapy

Convener: ANDREW FORBES (U. Witwatersrand)

209 Evaluation of the Phototoxic effect of Chemically Synthesized Silver Nanoparticles on Breast Cancer Cells

Silver nanoparticles (AgNPs) have attracted considerable interest in cancer therapy, whereby their cytotoxicity is largely associated with the production of reactive oxygen species (ROS), as well as interfering with cancer cell energy metabolism and multidrug resistance. Other than their inherent cytotoxic potential, AgNPs have advanced significantly as carriers for drug delivery, improving the stability and targeting efficiency and cancer diagnosis. Further, the ability of AgNPs to convert absorbed light into heat, thus effectively inducing localized hyperthermia to selectively target and destroy cancer cells attributed to their photothermal efficacy. This study investigates the cytotoxic and phototoxic efficacy of chemically synthesized AgNPs in the MCF-7 breast cancer cell line. The AgNPs were synthesized via chemical reduction and characterized using ultraviolet-visible spectroscopy, Zetasizer, and dynamic light scattering. MTT assay was conducted to evaluate the cell viability percentage with or without light irradiation at 5 J/cm2 with 405 nm blue light Diode Laser. Furthermore, the AgNPs-induced cell death was visualized with Bright Field Microscopy. The photothermal induced temperature increase of AgNP solution was measured with a Thermal Camera.
The UV-Vis spectra confirmed the formation of AgNPs with a characteristic surface plasmon resonance (SPR) band between 300 nm and 600 nm, with a maximum absorption peak observed at 402 nm. Further physicochemical analysis revealed an average hydrodynamic diameter of 119.3 dnm, a zeta potential of −30.8 mV, and a polydispersity index (PDI) of 0.269 at pH 7.65, indicating suitable size distribution, surface charge, and colloidal stability under physiological conditions. A dose-dependent cytotoxic response was observed across treated groups. At 5 µg/mL, MCF-7 cells exhibited 64.4% viability in the absence of irradiation, while exposure to 405 nm laser resulted in a reduced viability of 50.1%, demonstrating enhanced cytotoxicity following photoactivation. Without AgNP treatment, laser exposure alone produced a negligible ~1°C temperature increase. In contrast, AgNP-treated samples displayed a 3°C increase over 120 seconds of irradiation, confirming the nanoparticles’ photothermal conversion capability. The observed enhancement in cytotoxicity upon irradiation suggests a localized hyperthermic effect accompanied by plasmon-mediated generation of ROS. These findings support the contribution of both photothermal and photodynamic processes to the overall phototoxic efficacy of the AgNPs.
These results collectively demonstrate that AgNPs facilitate enhanced cancer cell death through the integration of photothermal and photodynamic mechanisms, supporting their potential application as photo-responsive agents in targeted cancer therapy.

Speaker: Isaac Baidoo (University of Johannesburg)

210 The Photo-Thermal Effect of Green-Synthesized Gold Nanoparticles on Human Breast Cancer Cells

Breast cancer continues to be one of the main causes of cancer-related deaths among women globally, highlighting the need for new, targeted, and less harmful treatment options. Gold nanoparticles (AuNPs) have been identified as potential tools in nanomedicine due to their compatibility with biological systems, customizable surface chemistry, and distinctive optical characteristics. Nevertheless, traditional synthesis methods often utilize toxic reducing agents, which limits their use in medicine. This study investigates an environmentally friendly method for synthesizing AuNPs using an extract from the Kniphofia porphyrantha plant and assesses their effectiveness in treating breast cancer. The AuNPs were synthesized through a green chemistry approach, utilizing aqueous plant extracts both as reducing and stabilizing agents. The spectrophotometric analysis was performed to confirm the optical properties of AuNPs. At the same time, the phototoxic effects of synthesized AuNPs on MCF-7 breast cancer cells were evaluated by assessing morphological changes, cellular viability, and cytotoxicity rates 24 hours post-irradiation using a 525 nm laser with a fluency of 10 J/cm². Results showed a dose-dependent response to the treatment, demonstrated by significant morphological changes, increased cytotoxicity, and decreased cell viability compared to untreated cells, indicating the anticancer properties of green AuNPs. This highlights the dual advantages of green AuNPs: sustainable production and potential use in cancer therapy. These results encourage further exploration of the optical properties and biological activity of plant-synthesized AuNPs as promising candidates for cancer nanomedicine.

Speaker: Mpho Mohlongo (University of Johannesburg)

211 Nanoformulation of Pheophorbide-a for Photodynamic Therapy in a Human Lung Cancer Spheroid Model

Pheophorbide a (PPBa) is a natural compound derived from chlorophyll, and its photophysical and photochemical properties makes it useful as a photosensitizer for photodynamic therapy (PDT). However, PPBa stability in biological environments and its bioavailability are crucial for effective therapy. Nanoparticle formulation of PPBa can improve its solubility and stability. The aim of this study is to make use of liposomal nanocomplex of PPBa as photosensitizer in PDT (at 15 J/cm2 fluency) on A549 spheroid cells. Thin-film hydration method was used for synthe-sis of NPs. Characterization of Lipo@PPBa were carried out using UV-Vis spectroscopy, TEM, SEM, FTIR and DLS. Moreover, cytotoxicity of NPs was evaluated at various concentrations via MTT assay. The IC50 dose was calculated for the evaluation of phototoxic effects under 660 nm laser irradiation at 15 J/cm2. UV-Vis spectroscopy showed a specific peak at 220 nm for lipids and two peaks for PPBa at 400 nm and 670 nm, respectively. TEM and SEM images il-lustrated that the size and shape of NPs were 45 nm and wavy crest, respectively. DLS data showed that the NPs have positive surface charge with zeta potential of 25 mV. MTT assay indicated that IC50 of Lipo@PPBa nanocomplex in PDT was 1 µM, which reduced the cell via-bility to 48%. In conclusion, Lipo@PPBa showed significant phototoxic effects on A549 sphe-roid cells. However, more investigations on targeted therapy using Lipo@PPBa is recommend-ed.

Speaker: Mr Kave Moloudi (Laser Research Centre, Faculty of Health Sciences, University of Johannesburg, Doornfontein, Johannesburg 2028, South Africa)

12:30 PM Breather

12:35 PM Lunch

1:45 PM Breather

Applied Physics

Convener: Alan Matthews (UKZN)

212 Characterising Photovoltaic Modules for Performance, Reliability, and Sustainability

Photovoltaic (PV) module characterisation plays an important role in understanding and optimizing the performance of solar PV energy systems. By rigorously analysing various parameters such as power output, efficiency, temperature dependence, spectral response, degradation mechanisms and failure rates researchers can fine-tune PV modules and systems for maximum energy output and durability. This characterisation process not only ensures reliable operation under diverse environmental conditions but also facilitates the development of more efficient, cost-effective and location appropriate PV technologies. In addition, it supports standardisation in efforts across the industry to facilitate comparisons between different module types and different deployment locations. Ultimately, robust characterisation enhances the overall reliability, performance, and longevity of PV systems. This advances their widespread acceptance, adoption and contribution to the Just Energy Transition to sustainable energy solutions globally. This paper introduces PV cell and module technology and highlights key standardised laboratory characterisation and in-field characterisation methods used on various PV systems ranging from domestic to utility-scale PV power plants.

Speaker: Ernest Van Dyk (Neslon Mandela University)

2:30 PM Applied Physics Division AGM

Astrophysics & Space Science: Division Meeting

Nuclear, Particle and Radiation Physics-1

Photonics: Biophotonics & PDT-Cancer Therapy

Convener: Angela Dudley

213 Photothermal Therapy Using Green-Synthesized gold Nanoparticles Derived from Senna didymobotrya: A Novel Strategy for Targeted Treatment of Melanoma Cells

Melanoma, a highly aggressive and metastatic form of skin cancer, frequently exhibits resistance to conventional treatments such as chemotherapy, radiation therapy, and surgical excision, highlighting the necessity for novel therapeutic approaches. Recently, integrating nanotechnology with photothermal therapy (PTT) has emerged as a promising strategy, offering targeted, minimally invasive therapeutic benefits. This study investigates the photothermal potential and underlying cytotoxic mechanisms of gold nanoparticles (AuNPs) biosynthesized using an aqueous extract of Senna didymobotrya against human melanoma A375 cells. Successful synthesis and formation of AuNPs were confirmed through UV-visible spectroscopy analysis. The photothermal efficacy of these nanoparticles was evaluated by assessing cellular viability through the MTT assay, reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP) disruption, and morphological changes via microscopic examination. Results revealed substantial photothermal efficiency, marked by significant temperature increases upon near-infrared (NIR) irradiation, leading to enhanced cytotoxicity in a dose-dependent manner. The cytotoxic mechanisms primarily involved ROS-induced mitochondrial dysfunction, ultimately resulting in apoptotic cell death. These findings underscore the significant potential of Senna didymobotrya-derived AuNPs as sustainable and potent photothermal agents, representing an encouraging advancement in melanoma treatment strategies.

Speaker: Mehak Zahra (Laser research centre)

214 Riboflavin-mediated Photodynamic Therapy Induces Cytotoxic Effects in A549 Lung Cancer Cells

Cancer is a deadly disease that continues to claim the lives of its victims on a global scale. Lung cancer, a prevalent and deadly malignancy, arises from the uncontrolled growth of cells within the lungs. Comprising of non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), this disease poses significant challenges in diagnosis and treatment. Therefore, there is a dire need to develop and introduce innovative solutions to effectively eradicate the disease. Photodynamic therapy has promising therapeutic effects while causing minimal harm to healthy cells and tissues. In the pursuit of advancing cancer treatments, this study explores the therapeutic potential and impact of riboflavin, a natural photosensitizer, and photodynamic therapy (PDT) against A549 lung cancer cells. The cells were treated with riboflavin at variable concentrations and irradiated using a laser of wavelength 470 nm and a fluency of 5 J/cm2. Following a period of 24 hrs post-irradiation, the A549 lung cancer cells were analyzed using a range of biochemical assays, namely adenosine triphosphate (ATP) and lactate dehydrogenase (LDH) assays to determine half maximal inhibitory concentration (IC50). In addition, morphological analysis post-irradiation and localization studies were performed to determine where the drug localizes in the organelles using a range of organelle-specific trackers, including markers for mitochondria, lysosome, and the endoplasmic reticulum. Moreover, a reactive oxygen species (ROS) detection assay was also performed for ROS quantification as a result of PDT. Changes in cell viability and morphology were observed post-treatment, indicating the cytotoxic effects of riboflavin-mediated PDT on A549 lung cancer cells. These findings suggest that riboflavin-mediated PDT has potential as an anticancer treatment for lung cancer.

Speaker: Malefo Tshepiso Seeletse (University of Johannesburg-Laser Research Centre)

215 Turmeric silver nanoparticles in melanoma photodynamic therapy

G Kah, and H Abrahamse
Laser Research Centre, Faculty of Health Sciences, University of Johannesburg, P.O. Box 17011, Doornfontein 2028, South Africa.

Email: habrahamse@uj.ac.za

Abstract. Melanoma is a very aggressive and lethal type of skin cancer due to its elevated propensity to spread to other organs. Melanoma treatment has advanced significantly in the past decades, with different treatment modalities, including chemotherapy, surgery, radiotherapy, immunotherapy, and targeted therapy, utilized to treat melanoma. However, these treatment options remain limited because of their inability to prevent resistance and disease progression. Photodynamic therapy (PDT) is a promising, less-invasive therapeutic method for treating neoplastic and premalignant lesions. It utilizes light of a specific wavelength to activate a photosensitizer, triggering reactive oxygen species production and subsequently causing cytotoxic cell damage and death. The purpose of this study is to examine the efficacy of turmeric-derived silver nanoparticles (TuAgNPs) in mediating melanoma PDT. TuAgNPs were synthesized and characterized using UV-vis spectroscopy, zeta potential analysis, and high-resolution transmission electron microscopy (HRTEM). A375 cells Melanoma cell lines (A375) were seeded and cultivated in complete media in an incubator set at 37°C, 85% humidity, and 5% CO₂. The cells were treated with different concentrations of TuAgNPs, then irradiated using laser light at a 430 nm wavelength and 5 J/cm². Post-laser irradiation assays, including MTT (3-(4,5-dimethylthazolk-2-yl)-2,5-diphenyl tetrazolium bromide), localization analysis, and morphological studies, were conducted to evaluate the cellular response of the treated cells. The TuAgNPs characterization analysis confirmed the formation of stable and spherically shaped nanoparticles. The localization analysis showed the cellular uptake and internalization of TuAgNPs in A375 cells. The MTT results indicated increased cytotoxicity in the treated cells, and morphological changes and deformations were observed in the PDT-treated cells. These findings suggest that TuAgNPs can serve as effective photosensitizers in melanoma PDT. Further, in vivo research could be required to assess the clinical efficacy of TuAgNPs-mediated PDT.

Speaker: Mrs Glory Kah (Laser Research Centre, Faculty of Health Sciences, University of Johannesburg, Doornfontein, Johannesburg 2028, South Africa)

216 Evaluation of Ce6 Photosensitisers-Induced Dark Toxicity and Phototoxicity (660 nm) on Melanoma Cells

Skin cancer may be classified into three types - cutaneous malignant melanoma, squamous cell carcinoma, and basal cell carcinoma. Radiotherapy, chemotherapy, targeted therapy, and immunotherapy are some of the traditional therapies, all of which present significant side effects. Photodynamic treatment has revolutionized cancer treatment because of its effectiveness against various cancer types and low side effect rates. One non-invasive, localized therapeutic option is photodynamic therapy. Photodynamic therapy (PDT) relies on a photosensitizer to create cytotoxic reactive oxygen species that destroy cancer cells. Since PDT's effectiveness primarily depends on the photosensitizer, much effort has been put into identifying the ideal one. Chlorin E6 (Ce6) is a second-generation photosensitizer that has FDA clearance and meets the clinical standards for PDT. Its potent ability to generate reactive oxygen species (ROS) and its potent anticancer impact on various cancer types are well established.
The phototoxic effects of Ce6 on the melanoma cancer cell line (A375) are examined in this study. The A375 cells were grown and maintained in a culture medium at 37° C, 5% CO2, and 85% humidity. The cells were subjected to a diode laser with a wavelength of 660 nm and gradually increasing concentrations of Ce6 photosensitizer. To ascertain how A375 cells responded to treatments, the cellular activities were assessed 24 hours after PDT using microscopy and biochemical testing. The substantial morphologic alterations, enhanced cytotoxic damage, and decreased cell viability and proliferation in PDT-treated cells demonstrated a dose-dependent response. Our findings reveal that Ce6 significantly inhibits the growth of A375 melanoma cells, offering a more precise and less toxic alternative to conventional treatments. Ce6 has shown success in treating melanoma cancer in vitro; however, when used clinically, the ensuing PDT efficacy will ultimately rely on biological characteristics. PDT might be regarded as an adjuvant treatment until established procedures for different tumor types and a relevant PS have been confirmed. These findings highlight the potential of Ce6-based PDT as a promising, targeted therapy for melanoma with reduced toxicity compared to conventional treatments.

Speaker: Aishat Obalola (University of Johannesburg)

217 Enhancing the Efficacy of Photodynamic Therapy: The Role of Hypocrellin B, Quercetin, and their combinations in Human Breast Cancer Cell Line

Photodynamic therapy (PDT) is an emerging treatment modality that utilizes photosensitizers and light to induce cytotoxic effects in cancer cells. This study investigates the combined therapeutic potential of hypocrellin B (HB) and quercetin (Quer) in PDT against human breast cancer cell lines. The primary objective was to evaluate the effects of PDT with HB, Quer, and their combination on cell viability, oxidative stress, mitochondrial integrity, and apoptosis in vitro. We utilized the MTT assay to assess cell viability post-PDT treatment, followed by the LDH assay to measure cellular membrane integrity. The ATP assay was employed to evaluate the energy status of cells after PDT, while reactive oxygen species (ROS) production was measured using a ROS assay to assess oxidative stress. Mitochondrial membrane potential was monitored to determine the effects on mitochondrial health. Finally, apoptosis was assessed using annexin V/PI staining and flow cytometry, which allowed for the detection of early and late apoptotic cells. The results revealed that combination therapy with HB and Quer significantly enhanced cytotoxicity compared to individual treatments, as evidenced by a marked decrease in cell viability, elevated ROS production, and loss of mitochondrial membrane potential. Furthermore, combined treatment induced a higher percentage of apoptosis, suggesting a synergistic effect between HB and Quer in enhancing PDT efficacy. These findings highlight the potential of HB and Quer as effective PDT agents for breast cancer therapy, supporting further exploration of their combination in clinical applications.

Speaker: Dr Sheeja S Rajan (University of Johannesburg)

Physics for Development, Education and Outreach: Physics in Industry Day

Physics of Condensed Matter and Materials

Theoretical and Computational Physics: Division group meeting

Conveners: Prof. Alan Cornell (University of Johannesburg), Prof. Azwinndini Muronga (Nelson Mandela University), William Horowitz (University of Cape Town)

Nuclear, Particle and Radiation Physics-2

218 Division Meeting

3:40 PM Afternoon Tea

Poster Session

Council Meeting with Divisions & Forums

WAADD

Fri, July 11

Plenary

9:15 AM Breather

Applied Physics

Convener: Tjaart Kruger

219 Ptychography in Ti64 alloy at the Diamond Light Source

We have studied a Ti6Al4V made by metal injection molding (MIM) using synchrotron X-ray imaging techniques. This alloy has superior mechanical properties compared with other titanium alloys [1]. We have managed to determine the porosity, defects, and the morphology using Computed Tomography and Ptychography.

Fabrication of the alloy was carried out at the Council for Scientific and Industrial Research (CSIR) in South Africa [2]. The MIM is a near-net shaping process that offers a unique ability to manufacture components with a wide range of porosity level which can provide useful scope to exploit various industrial applications [2].

Tomography was carried out at the European Synchrotron Radiation Facility, BM05 at a pixel sizes of 2.5 µm at an energy centered around 97 keV using a combination of aluminium and molybdenum filters and at 73 keV with 40 mm of SiO2 and 2.3 mm of Al as filters. A full volume reconstruction was carried out using PyHST2 software. According to these measurements, the porosity decreases as we move from the top of the specimen to the bottom. The inline phase contrast also shows that the elements are not uniformly distributed.

We have also carried out ptychography tomography measurements on the Ti6Al4V samples at the i13-1 Coherence beamline at the Diamond Light Source [3]. Two samples of cylindrical shape with a 10 µm radius were extracted using a focused ion beam (FIB). A monochromatic beam was used with a Fresnel zone plate lens to obtain the required probe size at the sample. Reconstruction of the projections was carried out using the ePIE algorithm implemented in PtyREX [4] and the reconstruction of the 3D volumes using TomoPy [5]. We will present the results obtained at nanometer resolution and the analysis.

References:
[1] Kolli, R. P. and Devaraj, A., (2018). A Review of Metastable Beta Titanium Alloys. Metals, 8.7 (2075-4701)
[2] Seerane, M. N. and Machaka, R., (2019). Metal injection moulding of 17-4PH stainless steel: Effects of porosity on the mechanical properties of the sintered products, IOP Conf. Ser.: Mater. Sci. Eng., 655 (012033)
[3] Rau, C., (2017). Imaging with Coherent Synchrotron Radiation: X-ray Imaging and Coherence Beamline (I13) at Diamond Light Source. Synchrotron Radiation News 30 (19–25)
[4] Batey, D. J., (2014). Ptychographic Imaging of Mixed States, University of Sheffield
[5] Gürsoy, D. et al., (2014). TomoPy: a framework for the analysis of synchrotron tomographic data, Journal of Synchrotron Radiation, 21(5) (1188–1193)

Speaker: Kudakwashe Jakata (Diamond Light Source)

220 Weather Forecasting Using Graph Neural Networks and Physics-informed Neural Networks

The weather plays a crucial role in decisions that people make on daily basis, especially in the agriculture, transportation, energy sectors. Therefore, accurate and efficient weather forecasting is of utmost significance. Predicting weather patterns has been an endeavor humanity has engaged in since ancient times. Over the years, various approaches have been used to forecast the weather. Currently, there are two main methods for weather forecasting: numerical modeling and machine learning (ML)-based modeling. Numerical modeling relies on complex numerical simulations of atmospheric physics, while ML-based modeling is data-driven and does not depend on such simulations. We explore the application of machine learning in weather forecasting, with a specific focus on two ML architectures: Graph Neural Networks (GNNs) and Physics-informed Neural Networks (PINNs). The GNNs model atmospheric interactions on a graph structure, while PINNs incorporate physical laws to constrain model learning and improve generalization. We also compare the performance of GNNs and PINNs in weather prediction. Our results demonstrate improved accuracy, efficiency, and enhanced prediction especially in capturing complex spatial and temporal relationships in weather data.

Speaker: Dr Mhlambululi Mafu (Case Western Reserve University)

221 Reconfigurable Payload Power Management System for Rockets

In general, a rocket's onboard systems, including payloads, must be harmonized within the overall system. In some cases, payloads with an autonomous power system, including batteries, must be activated shortly before or after launch to keep the mission active for the required time. The sizing of power switches must be done according to the power requirements of the payloads, and it is also necessary to size the connections between the parts to limit issues related to ground loops. If the payload specifications change, reconfiguring or resizing the Power Management System (PMS) board may be necessary, but it is not strictly required.

The proposed system has been designed to be reconfigurable and geometrically symmetric to maintain the center of mass on the rocket's symmetric axis. Once inserted into the rocket's nose cone, the system is completely powered off and can be activated remotely using a wireless system. Once activated, the Payload Power Management System (PMS) will be able to receive RF instructions and activate or deactivate payloads according to mission requirements.

Speaker: Marco Mariola (University of KwaZulu-Natal)

Astrophysics & Space Science 2

Astrophysics & Space Science: Astrophysics and Space Science - Space Science Session 5

Convener: Joseph Omojola (North-West University)

222 Cosmic-Ray Neutron Detectors for Soil Moisture Monitoring

Primary cosmic rays are high-energy particles that enter the Earth’s atmosphere via the heliosphere,
which generate cascades of secondary cosmic-ray particles when interacting with atmospheric
atoms. These secondary cosmic-rays interact inversely with hydrogen atoms in soil moisture,
providing a non-invasive method for monitoring moisture levels. Continuous measurements
of neutron flux in soil can establish predictive models for heatwaves, droughts, and floods that
significantly impact South Africa’s agricultural sector. This study employs a cosmic-ray neutron
sensor (CRNS) probe equipped with a Boron trifluoride (BF3) detector positioned 1-2 m above
ground that is capable of measuring soil moisture across a footprint of approximately 20 hectares
width and up to 0.3 m depth. We detail the calibration process relating measured neutron intensity
to volumetric water content, validated against gravimetric soil sampling and point sensor data,
which will assist in precision agriculture that can enhance water resource management in diverse
agricultural landscapes across South Africa.

Speaker: Aimee Dumont

223 Solar wind temperature anisotropy during the Ulysses Spacecraft first polar pass

Anisotropy is a property of turbulence in solar wind plasma in which velocity and magnetic fields
fluctuate along and perpendicular to the ambient magnetic field. Recent in situ measurements
confirmed that the solar wind in the inner heliosphere exhibits a temperature anisotropy. The
presence of this anisotropy results in magnetohydrodynamic (MHD) waves and instabilities. In
this report, we analyze the proton temperature anisotropy using data from the Ulysses spacecraft
during its first latitude scan. Radial and latitudinal variations of temperature anisotropy for Firehose
and Mirror instabilities are discussed.

Speaker: Ephrem Tesfaye Desta (Centre for Space Research, North-West University)

224 An investigative numerical modelling study of galactic deuterons in the heliosphere

The observation of galactic cosmic ray (GCR) deuteron at the Earth has been done precisely with
the PAMELA and AMS02 space detectors and reported from July 2006 to September 2014 and
from May 2011 to April 2021, respectively. These observations span time frames that include solar
maximum and both minimum modulation conditions in the A > 0 and A < 0 magnetic field cycles
at rigidities between ~ 0.75 GV and ~ 19.5 GV. A surprise from AMS02 observation was that current
available GALPROP calculated deuteron local interstellar spectra (LIS) are unable to reproduce the
deuteron observations at rigidities above ~5 GV, and thus challenging the status quo regarding
their origin in the galaxy. In this study a comprehensive 3D numerical model and a set of diffusion
and drift coefficients, previously applied to a number of cosmic ray nuclei, together with a newly
estimated LIS for deuterons, are used to simulate the modulation of deuterons from July 2006 to
April 2021. The modelling results will be compared to observations made by PAMELA and AMS-02
detectors. This study will illustrate and discuss the effects due to different LISs and those caused by
the main modulation mechanisms on deuteron modulation at the Earth. Furthermore, differences
between the modulation of protons and deuterons at the Earth will be uncovered and highlighted.

Speaker: Innocentia Itumeleng Ramokgaba (Centre of Space Research, North-west University, Potchefstroom, South Africa)

Astrophysics & Space Science: Miscellaneous astrophysics

225 Trends of Thermal Structure in the MLT Region Using SABER Observations Over Sutherland, South Africa

The Mesosphere and Lower Thermosphere (MLT) region of the upper atmosphere is an essential atmospheric layer that significantly influences energy exchange, atmospheric dynamics, and space weather interactions. Comprehending the temperature of the MLT is essential, as this region acts as a critical interface between Earth's atmosphere and outer space, with its temperature directly affecting several physical and environmental processes. Moreover, the MLT temperature data interprets the vertical transfer of energy and momentum in the atmosphere. The Thermosphere Ionosphere Mesosphere Energetics Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry (TIMED/SABER) instrument is a crucial observational tool for examining the MLT area, offering long-term temperature observations to analyze trends and fluctuations in atmospheric parameters. The primary objective of this research is to examine the trend and variability of the thermal structure in the MLT region utilizing data collected by the TIMED/SABER satellite in Sutherland, South Africa. The TrendRUN model simulates and elucidates the long-term thermal structure trends in the MLT, employing realistic external forcings such as solar cycle variability, El Niño-Southern Oscillation, Quasi-Biennial Oscillation (QBO), yearly cycle, and semiannual cycle. The Mann-Kendall and Sequential Mann-Kendall nonparametric trend test methods are employed to extract trends. This research demonstrates that SABER data imply prolonged cooling trends, especially in the mesosphere, along with increasing CO₂ concentrations.

Speaker: Blessing Mvana Nhlozi

226 Nuggets at the heart of nearby galaxies - -NGC2865

In this talk, I will show recent results from the deep optical imaging and spectroscopic study of the spectacular nearby galaxy NGC2865.
NGC2865 is well-known for its system of relatively bright stellar shells in the galaxy's outskirts believed to be remnants of a recent merger event. I will, however, unveil a remarkable but hidden stellar feature at the centre of this galaxy which is directly related to this merger event.
I will show how the combined data from HST imaging, SALT/RSS and VLT/MUSE spectral data help us to unambiguously constrain the nature of the merger event that produced these spectacular stellar features as well as the nature of the disrupted progenitor. I will also discuss the implications of our results, i.e., the decoupled kinematics of the central 'nugget' in NGC 2865 and its stellar population properties (age, metallicity, star-formation histories), in the context of expectations from
recent cosmological simulations.

Speaker: Dr Adebusola Alabi (North-West University)

227 Stochastic particle acceleration by multifractal MHD turbulence in strong magnetic fields

Enrico Fermi first proposed the stochastic acceleration of protons due to interactions with parsec-scale interstellar magnetic fields as a method of cosmic ray acceleration around the time of the 1950s. Since then, the theoretical framework of stochastic acceleration in magnetohydrodynamic (MHD) turbulence has undergone significant refinement with recent numerical simulations incorporating more realistic multifractal MHD turbulence yielding previously unknown effects, such as intermittent particle energization characterized by large jumps in particle momenta. In this work, we numerically simulate the intermittent acceleration of a population of relativistic electrons as a continuous-time random walk, i.e., the time between energization events is described by a continuous random variable, based on the methodology developed in previous studies. We developed a Monte-Carlo code to simulate the effects of intermittent energization on the electron spectrum. This methodology was extended by incorporating intermittent synchrotron cooling into the existing theory for which an analytical expression for the change in electron momentum was found and incorporated into the Monte-Carlo approach. Our findings suggest particle spectra characterized by distinct low- and high-energy tails, differing significantly from those predicted by the standard Fermi theory.

Speaker: Frans van der Merwe (North-West University)

Nuclear, Particle and Radiation Physics-1

Photonics: Biophotonics & PDT-Cancer Therapy

Convener: Isaac Nape (University of the Witwatersrand)

228 Evaluation of Pheophorbide a Phototoxicity in Melanoma Cells Grown as Three-Dimensional Multicellular Tumour Spheroids

Melanoma is the deadliest form of skin cancer, with a rapidly increasing incidence and a poor prognosis for patients diagnosed at advanced stages. Despite several available treatments, including surgical excision, chemotherapy, radiation therapy, and immunotherapy, resistance to these therapies remains a significant challenge, particularly when the tumour has metastasised. Photodynamic therapy (PDT) is a promising modality for the treatment of cancer because it is non-invasive and selectively damages the cancerous tissue, minimizing damage to adjacent healthy tissues. Currently, most PDT experiments are still conducted on two-dimensional (2-D) monocultures, which fail to accurately mimic native three-dimensional (3-D) tissue architecture. Therefore, 3-D cell cultures serve as excellent models to resemble tumour tissue in terms of structural and functional properties. Commercially purchased A375 melanoma cells used in this study were cultured as 3-D tumour spheroids and treated with pheophorbide-a at varying doses (1-40 M) and irradiated at a fluency of 10 J/cm2 with a 660 nm diode laser. Post-irradiation cellular changes were observed using microscopy, adenosine 5′-triphosphate (ATP), and lactate dehydrogenase (LDH) assays. Photoactivated pheophorbide a led to a significant dose-dependent response to PDT, demonstrating notable morphologic changes, increased cytotoxicity, and reduced cell viability. The study indicated that PDT with pheophorbide-a is an effective treatment method for eradicating melanoma cancer cells in vitro.

Speaker: Dr Nkune Nkune (Laser Research Centre, Faculty of Health Sciences, University of Johannesburg)

229 In vitro evaluation of hypocrellin B based-photodynamic therapy on human oesophageal cancer HKESC-1 cells

Background: Oesophageal cancer is a malignant disease that accounts for the seventh major cause of cancer-associated death worldwide. Hypocrellin B, a natural photosensitizer, has been employed for photodynamic therapy for various neoplastic diseases. However, studies that utilize hypocrellin B-based- photodynamic therapy on oesophageal cancer are limited. This current study examined the in vitro effects of hypocrellin B-based-photodynamic therapy on human oesophageal cancer cells.
Materials and methods: Human oesophageal cancer HKESC-1 cells were grouped into non-photodynamic and photodynamic therapy groups. Both groups were treated with varying concentrations of hypocrellin B. After four hours, the photodynamic therapy category was irradiated at a fluency of 5 J/cm2 and a wavelength of 470nm. Twenty-four-hour post-irradiation cell viability, lactate dehydrogenase (LDH) release and damage to the mitochondrial and nuclear morphological assessments were performed.
Results: Treatment with hypocrellin B-mediated photodynamic therapy significantly reduced the amount of ATP/viability of HKESC-1 cells, and the amount of LDH released was notably higher in the photodynamic therapy group. Mitochondrial membrane potential was impaired, and nuclear condensation was markedly observed in the hypocrellin B-mediated photodynamic therapy.
Conclusion: Hypocrellin-B mediated photodynamic therapy demonstrated remarkable anticancer activities in oesophageal cancer HKESC-1 cells.

Speaker: Onyisi Christiana Didamson (Laser Research Centre, Faculty of Health Sciences, University of Johannesburg, Doornfontein, Johannesburg 2028, South Africa)

230 RELATIVE PHASE EFFECT ON HIGH-ORDER HARMONIC GENERATION IN AN INHOMOGENEOUS TWO-COLOR LASER FIELD

A theoretical investigation of the effect of the polarization angle on high-order harmonic generation in an inhomogeneous two-color field is reported. The results show that the use of two-color fields greatly enhanced the harmonic cutoff point in comparison with the one-color field from 70th to 90th orders in a homogeneous field. In addition, the introduction of an inhomogeneity parameter of 0.003 generated a broad supercontinuum of approximately 270 orders. However, an increase in the polarization angle adversely affected the harmonic cutoff.

Speaker: Dr Dr. stephen maina Njoroge (karatina University)

Physics for Development, Education and Outreach

Convener: Deena Naidoo (University of the Witwatersrand)

231 African collaborations and related benefits

In this paper, I will present on the successful collaborations and initiatives in physics in Africa. There are available funding streams for Africa collaborations from South African NRF and MRC. The examples of bilateral funding between South Africa-Zambia, SA-Egypt, and SA-Algeria, to mention but a few, have continued for many years, benefiting many South African researchers. The collaboration with Africa allows for South Africa to train brilliant minds from Africa and receive innovations for the continent. Physics initiatives like Fundamental Physics program and conference, focusing on high energy physics, ASESMA for electronic materials and structure, taking place bi-annually, traveling in Africa, and AIMS with offices in West-Africa, East Africa and South Africa are important for IUPAP - C13 - physics for development. In addition, there are also international funding like EU-Africa, SWISS-South Africa-Africa, French-South Africa and Astronomy related projects. The funded projects by South Africa at ESR, CERN, and JINR are benefiting Africa and relate to addressing skills issues for development. A recent example to EU funded project, managed by SANEDI is LEAP-RE which has produced a motorbike which was tested here in Africa, with University of Stellenbosch and Kenya. The bike was driven from Nairobi to Stellenbosch and completed the trip successfully. Also, the Africa- Materials Research Society (AMRS) taking place bi-annually is a very successful inter-disciplinary, intra-disciplinary project towards African development and attaining sustainable development goals

Speaker: Prof. Mmantsae Moche Diale (University of Preoria)

232 Electrical Transport Measurements from First Principles: a Senior Undergraduate Experiment

A final year undergraduate experiment has been designed and constructed with the aim of illustrating numerous aspects of low temperature measurements, with the objective of determining the electrical transport properties of materials. The experiment is designed to ensure that the students cannot treat the experimental apparatus as a data-producing “black box”, and the students are obliged to manually control the temperature, take much of the data by hand, and to calibrate the thermocouple used to measure the temperature. The use of a desktop computer and software packages during the experiment are encouraged. Much of the apparatus was assembled at relatively low cost.

Speaker: Jonathan Keartland (School of Physics, WITS)

233 Exploring Curriculum Considerations to Prepare Future Radiographers for an AI-Assisted Health Care Environment: Protocol for Scoping Review

The use of artificial intelligence (AI) technologies in radiography practice is increasing. As this advanced technology becomes more embedded in radiography systems and clinical practice, the role of radiographers will evolve. In the context of these anticipated changes, it may be reasonable to expect modifications to the competencies and educational requirements of current and future practitioners to ensure successful AI adoption.

The review aims to explore and synthesize the literature on the adjustments needed in the radiography curriculum to prepare radiography students for the demands of AI-assisted health care environments.

Using the Joanna Briggs Institute methodology, an initial search was run in Scopus to determine whether the search strategy that was developed with a library specialist would capture the relevant literature by screening the title and abstract of the first 50 articles. Additional search terms identified in the articles were added to the search strategy. Next, EBSCOhost, PubMed, and Web of Science databases were searched. In total, 2 reviewers will independently review the title, abstract, and full-text articles according to the predefined inclusion and exclusion criteria, with conflicts resolved by a third reviewer.

The search results will be reported using the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews) checklist. The final scoping review will present the data analysis as findings in tabular form and through narrative descriptions. The final database searches were completed in October 2024 and yielded 2224 records. Title and abstract screening of 1930 articles is underway after removing 294 duplicates. The scoping review is expected
to be finalized by the end of May 2025.

A scoping review aims to systematically map the evidence on the adjustments needed in the radiography curriculum to prepare radiography students for the integration of AI technologies in the health care environment. It is relevant to map the evidence because increased integration of AI-based technologies in clinical practice has been noted and changes in practice must be underpinned by appropriate education and training. The findings in this study will provide a better understanding of how the radiography curriculum should adapt to meet the educational needs of current and future radiographers to ensure competent and
safe practice in response to AI technologies.

Speaker: Ms Chamandra Kammies (University of Johannesburg)

Physics of Condensed Matter and Materials

Theoretical and Computational Physics

Physics for Development, Education and Outreach

Convener: Jonathan Keartland (School of Physics, WITS)

10:20 AM Morning Tea

Applied Physics

Convener: Alan Matthews (UKZN)

234 Exciting applications for a turn-key structured light generator

Many applications exist for structured light. However, a barrier of entry exists for non-experts. Button Optics has created an all-in-one solution for generating different kinds of beams. Over the last year we have created a fully functional product interfacing with cameras and computer software. Moreover, we have expanded our product suite to include a diagnostic device. In this talk I will highlight some of the applications that are relevant for the immediate future and also our longer-term plans.

Speaker: Bertus Jordaan (University of the Witwatersrand)

235 On the practicality of Quantum Machine Learning in Africa

Quantum machine learning (QML) is an exciting new field of study which in one respect harnesses the laws of quantum mechanics and applies it to classical machine learning models. QML has a wide variety of potential applications spanning many fields which include healthcare and life sciences, climate and sustainability, finance and optimization. Two parallel activities have emerged to pioneer the field of quantum discoveries: one is the technological advancements required (hardware, software and algorithms) and the other is the rapid exploration of domain-specific problems towards identifying quantum advantage over classical methods.

In this talk, we will provide the participants with an introduction to QML from a theoretical perspective, describe pioneering results reported by IBM Quantum and provide insight on the opportunities available for getting started in Qiskit. This talk is aimed at the academic and industry audience alike, as well as those more junior to the field of quantum machine learning, and those more experienced in running experiments using Qiskit.

Speaker: Stephanie Muller (IBM Research)

236 GeoQAI: A Quantum Machine Learning Paradigm with Geospatial Data

Quantum Machine Learning (QML) lies at the intersection of classical Machine Learning (ML) and Quantum Computing (QC) and is currently experiencing significant growth in terms of both efficiency and applications. This expansion is largely driven by the availability of Noisy Intermediate-Scale Quantum (NISQ) processors, which enable the use of Quantum Computing without needing to tackle the challenges of error correction. As a result, there has been a surge in Quantum Computing applications, including QML. However, most QML implementations to date have relied on generic classical ML datasets, such as the Iris dataset, MNIST (Modified National Institute of Standards) dataset, and Fashion MNIST dataset. In this work, we introduce a novel QML paradigm called GeoQAI (Geospatial Quantum Artificial Intelligence). This paradigm explores the application of Quantum Machine Learning to geospatial data. Our goal is to unlock deeper insights into spatial dynamics, improve predictive capabilities, and facilitate better decision-making in various fields, including environmental science, urban planning, and resource management. Furthermore, we report on the use of QML for Land Use and Land Cover (LULC) classification. The results obtained in this study suggest the potential for further investigation into the GeoQAI paradigm, particularly for exploring QML applications in other geospatial contexts beyond LULC. This work provides insights on improving the accuracy and efficiency of spatial analysis tasks and developing new tools and frameworks for integrating geographic information systems with other disciplines.

Speaker: Dr Makhamisa Senekane (University of Johannesburg)

Astrophysics & Space Science 2

Astrophysics & Space Science: Astrophysics and Space Science - Space Science Session 6

Convener: Joseph Omojola (North-West University)

237 Investigating the photospheric and chromospheric response of a C-class solar flare on 1 July 2012 using Swedish Solar Telescope and SDO observations

The C-class solar flare event of 1 July 2012 13:08 UTC was observed in multiple wavelengths by
the 1-m Swedish Solar Telescope (SST), providing information about the state of the photosphere,
chromosphere and corona. In this study, focus is placed on the changes in sheared photospheric
flow pre and post flare. Magnetic features inside the flow pattern are tracked, the borders between
several counter flows and the location of different polarity inversion lines are identified, while the
spatial evolution over time of the magnetic features is monitored for changes in magnetic field line
tension. The magnetic flux is calculated for each magnetic feature and the velocity flow vectors
are determined to show the degree of shearing pre and post flare. The SST results are combined
with results from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic
Imager (HMI) instruments on board the Solar Dynamics Observatory.

Speaker: Ruhann Steyn (Centre for Space Research, North-West University)

Astrophysics & Space Science: High energy astrophysics

238 A Temporal-spectral study of short gamma-ray transients: Identifying distinct signatures of gamma-ray bursts and magnetar giant flares

Short gamma-ray bursts (SGRBs) and magnetar giant flares (MGFs) are short gamma-ray transients (SGRTs) with similar temporal profiles but distinct progenitors—SGRBs arise from compact binary mergers, while MGFs originate from magnetars in nearby galaxies. When MGFs are observed at large distances, their characteristic fading pulses may be undetectable, making them difficult to distinguish from single-pulsed SGRBs, particularly in the absence of redshift information. This study analyses the temporal and spectral properties of redshift-known SGRBs detected by Fermi-GBM and two Fermi-detected MGFs, GRB200415A and GRB231115A. Pulse rise times, obtained via Norris function fits, reveal that MGFs exhibit significantly faster rise times than SGRBs. Spectral analysis over the 10 keV–40 MeV range using Comptonized and Band models shows that MGFs have much harder low-energy spectral indices. These differences support the interpretation that MGFs result from rapid energy release near a magnetar’s surface, while SGRB emissions are likely driven by internal shocks at larger radii from the central engine.

Speaker: Dimakatso Maheso

239 Multi-Wavelength Observations of AGN Activity in the Fornax Cluster

Active Galactic Nuclei (AGN) play a critical role in regulating and shaping galaxy evolution through various influential processes or mechanisms that impact the surrounding interstellar and intergalactic medium. In dense environments such as galaxy clusters, this interplay becomes even more complex due to environmental effects like ram pressure stripping, tidal interactions, and strangulation. In this talk, I will discuss AGN-host galaxies in the Fornax Cluster using Multi-wavelength observations from MeerKAT (probing neutral hydrogen gas), MUSE/VLT (resolving ionised gas and stellar kinematics), and eROSITA (tracing hot X-ray emitting gas). With this multi-wavelength observations of galaxies across three key gas phases: cold (HI), warm (ionised), and hot (X-ray). We will uncover signatures of AGN feedback, gas accretion or stripping, and environmental suppression of star formation. With this ongoing project, we will constrain how AGN influences their host galaxies and how the cluster environment modulates gas content and AGN activity and to our broader understanding of galaxy transformation in clusters and the role of AGN in quenching or fuelling galaxies within such environments.

Speaker: Dejene Zewdie Woldeyes (North-West University)

240 Late-time spectropolarimetry of GRB 250129A: evidence of an off-axis Gaussian jet

Gamma-Ray Burst (GRB) afterglows arise from the interaction of relativistic ejecta with the circumburst medium and are observed across the electromagnetic spectrum. Polarisation is expected during the early and late phases of the afterglow depending on the presence of reverse shocks and the viewing geometry of the jet. Polarimetric observations of GRB afterglows serve as a unique diagnostic tool to investigate the geometry and structure of magnetic fields in the emitting region, which cannot be directly inferred from photometric or spectroscopic data alone. We present late-time spectropolarimetric observations of GRB 250129A using the Robert Stobie Spectrograph on the Southern African Large Telescope (SALT), obtained $\sim$19 hours post-burst. We detect a remarkably high linear polarisation of 5–10 % and a $> 90^{\circ}$ rotation in polarisation angle across wavelength—an unprecedented result for this late afterglow phase. This indicates turbulence with large-scale toroidal and radially stretched magnetic-field structures in the late-time forward shock regime. Such high polarisation levels are typically expected during the early afterglow ($\sim$100 s) when reverse shocks dominate. However, multi-wavelength observations from LCO, DOT, ZEISS, and Swift-XRT show no indication of reverse shock contribution at this epoch. XRT data reveals high-latitude emission and the flaring activity between 5.5 and 11 hours since the explosion. Afterglow modeling incorporating both forward and reverse shocks confirms that the reverse shock component fades rapidly after $\sim$100 s. The multi-wavelength afterglow is best explained by an off-axis viewing geometry ($\sim 11^{\circ}$ from the jet axis) of a Gaussian jet in a uniform density ISM environment. GRB 250129A thus provides rare observational evidence linking late-time polarisation to geometric and jet-structure effects.

Speaker: Ankur Ghosh (University of Johannesburg)

241 Exploring ULXs as Short GRB Precursors

The joint detection of gravitational waves (GW170817) by LIGO and Virgo, together with the short gamma-ray burst (sGRBs) GRB 170817A observed by Fermi and INTEGRAL, has confirmed that at least some sGRBs originate
from the merger of two neutron stars (NS-NS). Despite this breakthrough, the evolutionary pathways that lead to such
mergers remain uncertain.

In this project, we study the likelihood that a binary system which undergoes a ULX phase will ultimately produce an sGRB. To do this, we use the rapid population synthesis code COSMIC to simulate large ensembles of massive binary systems across a range of metallicities and generate our ULX population. We use a detailed binary evolution code POSYDON to complement these statistical results to model selected ULX systems with more realistic mass transfer physics and common-envelope evolution. Our study aims to quantify the fraction of ULX systems that lead to sGRB-producing compact mergers and to characterize their delay time distributions and likely host galaxy properties.

Speaker: Lutendo Nyadzani (University of Johannesburg)

242 Compton-induced cascade $\gamma$-rays in the radio galaxy NGC 1275

Among the active galactic nuclei (AGNi), blazars are the brightest emitters of high- (HE, $E \ge 100\,\mathrm{MeV}$) to very-high-energy (VHE, $E \geq 100\,\mathrm{GeV}$) $\gamma$-rays from their jets. Radio galaxies, being the misaligned parent population of the blazar class, were historically not observed at these frequencies. However, there is a growing number of radio galaxies detected in HE--VHE $\gamma$-rays in recent years. In this work, we leverage and refine a Monte-Carlo photon and electron-positron ($e^\pm$) tracking code in the AGN environment of the radio galaxy NGC 1275. In the code, we consider the isotropic broad emission line and Shakura-Sunyaev (SS) accretion disk radiation fields, with mild magnetic fields in the AGN environment. We find that cascade $\gamma$-rays from the inverse-Compton scattering by relativistic $e^\pm$ pairs of these external radiation fields can explain the \emph{Fermi} Large Area Telescope’s (LAT) observation of the radio galaxy NGC 1275. We present a set of parameters obtained from the code and fit the source’s spectral energy distribution during the flaring events recorded in December 2022 and January 2023.

Speaker: Ntshatsha Mfuphi

Nuclear, Particle and Radiation Physics-1

Nuclear, Particle and Radiation Physics-2

243 Probing Charged Current B-anomalies via a U (1)μ−τ Extension of the Standard Model

The lepton flavor universality ratios $R(D)$ and $R(D^{*})$, defined as $R_{D^{(*)}} \equiv \mathcal{B}(\bar{B}\to D^{(*)} \tau^{-} \bar{\nu}_{\tau})/\mathcal{B}(\bar{B} \to D^{(*)} \ell^{-} \bar{\nu}_{\ell})$ where$(\ell = e, \mu)$, are measured in semi-leptonic $B$ decays and serve as sensitive probes of new physics beyond the Standard Model (SM). Recent experimental averages, $R(D) = 0.342 \pm 0.026$ and $R(D^*) = 0.287 \pm 0.012$, show a combined deviation of $3.2\sigma$ from SM predictions, indicating the possibility of new physics in semi-leptonic $B$ meson decays. We base our attention on the Charge Current$(CC)$ process $b\to c\tau^{-}\bar{\nu_{\tau}}$, where we explore this process using a well-motivated extension of the SM, featuring a $U(1)_{\mu - \tau}$ gauge symmetry. The model introduces new vector-like quark doublets $( Q'_a )$ and a singlet scalar $( \chi )$, both charged under $U(1)_{\mu - \tau}$ and odd under $Z_2$ symmetry. The corresponding Wilson coefficients are derived and a $\chi^2$-fit is performed with the current experimental data to constrain the model parameters.

Speaker: Mr Vuyolwethu Happyboy Kakancu (University of Witwatersrand)

244 Analysing h to Zy decay at the Large Hadron Collider using SMEFT

The ATLAS and CMS collaborations have jointly reported the first evidence of the Higgs boson ($h$) decay into a $Z$ boson and a photon, with a statistical significance of $3.4\sigma$. The observed signal strength, $2.2 \pm 0.7$ times the Standard Model (SM) expectation, exceeds the SM prediction even when next-to-leading order (NLO) QCD corrections and signal-background interference are taken into account. This persistent deviation motivates an interpretation in the context of the Standard Model Effective Field Theory (SMEFT). In this study, we investigate the $h \to Z\gamma$ decay process at the LHC, focusing on gluon-gluon fusion (ggF) as the primary production mechanism. We aim to constrain the relevant dimension-six SMEFT operators by fitting model parameters to cross-section measurements and differential kinematic distributions that are sensitive to new physics. To improve the efficiency of this exploration, we employ kinematic interpolation methods across the SMEFT parameter space. Beyond the ggF channel, we also investigate additional Higgs production mechanisms including vector boson fusion (VBF), associated production with top quarks (ttH), and vector bosons (VH) to capture a broader range of dynamics and improve the robustness of the SMEFT interpretation. Multiple $Z$ decay final states are considered, including leptonic ($Z \to \ell^+\ell^-$) and hadronic ($Z \to jj$) modes, to maximize signal acceptance and provide complementary constraints on new physics scenarios.

Speaker: Njokweni Mbuyiswa (University of the Witwatersrand)

245 The use of Machine Learning techniques to analyse the h-> Zy process within the SMEFT framework at the Large Hadron Collider (LHC)

Building on the ATLAS and CMS discovery of the Higgs boson decaying into a $Z$-boson and a photon (with a 3.4$\sigma$ significance), the current Standard Model (SM) predictions for the $h \to Z\gamma$ signal rate exceed the measured value by $2.4 \pm 0.9$, indicating possible new physics effects or systematic uncertainties that warrant further investigation. This analysis investigates this rare process using machine learning techniques where we employ classifiers such as the Boosted Decision Trees (BDT), XGBoost, and the kernel density estimation to analyse the production modes of $h\to Z\gamma$ including gluon-gluon fusion (ggF), vector boson fusion (VBF), associated production with a vector boson (VH), and associated production with a top quark pair (ttH), within the framework of the Standard Model Effective Field Theory (SMEFT). This machine-learning approach aims to constrain the six-dimensional Wilson coefficients and shed light on potential deviations from SM prediction.

Speaker: Kutlwano Makgetha (University of the Witwatersrand)

246 Comparison of Full and Fast Simulation Efficiencies in the ATLAS Detector Using Tag-and-Probe and EGamma MC Comparison Frameworks

Monte Carlo (MC) simulated data are essential for modeling events in the ATLAS Inner Detector. However, full Geant4-based simulations have become increasingly computationally demanding, with approximately 80% of the processing time attributed to shower simulation and detailed ATLAS detector geometry modeling. To address this, the new ATLAS Fast Simulation (AF3) framework provides a parameterized response for particles entering the calorimeters, using a simplified detector geometry to approximate energy deposition in calorimeter cells.

In this study, identification and reconstruction efficiencies—and their associated scale factors—were evaluated to compare the performance of Full and Fast simulations. Two methods were employed: the conventional Tag-and-Probe technique, which operates at the event level, and the new EGamma Full-Fast MC Comparison tool (EGMCE), which applies a particle-counting approach for assessing efficiencies.
Results showed overall good agreement between Fast and Full simulations across both methods showing the accurate modelling of Fast simulations whilst retaining similar results to Full simulations. However, the EGMCE framework exhibited lower reconstruction efficiencies, primarily due to challenges in correctly identifying electrons reconstructed as photons. Similarly, discrepancies were observed in identification efficiency: while the EGMCE tool showed agreement with AF3 efficiencies in the 80–90% range, it deviated from those obtained via Full simulation.

The findings demonstrate the need for further refinement of the EGMCE framework in its particle selection algorithms to ensure consistency with the Tag-and-Probe method and reliability for future physics analyses within analysis groups

Speaker: Abdool Sattar Cassim (University of Johannesburg)

247 Orthogonality study for the A/S→ZdZd→2l2v/2l2j with the ATLAS detector at the LHC

The hidden abelian Higgs model is used for a search for an additional scalar decaying to two Z-dark bosons (Zd) to two leptons, two neutrinos (2l2v) . The search uses 𝑝𝑝 collision data collected with the ATLAS detector at the LHC with an integrated luminosity of 139 fb⁻¹ at a centre-of-mass energy √s= 13 TeV . This is a follow up to the study of the 4l final states [1]. In our 2l2v channel analysis, using the HAHM on Run-2 and Run-3 data with the ATLAS detector to conduct the search for an additional scalar with a distinct mass from the Higgs boson demands study of signal overlap from the 2l2j channel. A technique is introduced to separate signal events of our 2l2v channel from that of the 2l2j channel . We present the work and result of orthogonality study done to achieve this.

[1] ATLAS Collaboration. (2024). Search for a new scalar decaying into new spin-1 bosons in four-lepton final states with the ATLAS detector (CERN-EP-2024-248). arXiv:2410.16781 [hep-ex].

Speaker: Doomnull Unwuchola (University of the Western Cape)

Photonics: OPEN SLOT

Convener: Angela Dudley

Physics for Development, Education and Outreach

Convener: Sam Ramaila

248 PLAYand Brain Awareness – The missing link in STEM education

This article motivates and describes how play could be implemented at school, home and during therapies to help young children not only master maths concepts, but develop a positive study orientation towards maths and science. Research findings indicate that emotional intelligence, study orientation, motivation, resilience can predict not only the mathematics achievement of middle adolescents, but are also linked to increased likelihood of taking advanced mathematics courses. Developing emotional intelligence and study orientation in mathematics may be a vital missing link in maths achievement and should start at a very young age when the brain is still developing. Children learn through play. Most of the young child’s thought processes are non-verbal and pictures and images are the most effective teaching media. Young children also need to be creative when discovering the world of maths. Children must touch maths and they need a variety of activities to keep their attention, and to help them develop concentration.

Keywords: mathematics; play; emotional intelligence; mathematics achievement; mathematics anxiety; metacognition; .play therapy; puppet therapy; brain development, biblio-therapy; resilience: study orientation in mathematics.

Speaker: Petro Erasmus

Physics for Development, Education and Outreach: SAPhysNet Hybrid Meeting

Convener: Prof. Azwinndini Muronga (Nelson Mandela University)

Physics of Condensed Matter and Materials

Theoretical and Computational Physics

Photonics: Non-Specialist Talk

Convener: Angela Dudley

Photonics: Photonics Division Meeting

Convener: Angela Dudley

12:30 PM Breather

12:35 PM Lunch

1:45 PM Breather

Plenary

2:35 PM Breather

AGM

Gala Dinner