Speaker
Description
Measurement of angular correlations in $\gamma-\gamma$ cascades using coincidence detection and Monte Carlo simulation
M. Chaplin, T. Hutton, T. Leadbeater
Metrological and Applied Sciences University Research Unit, Department of Physics,
University of Cape Town, South Africa.
Coincidence counting techniques are widely used to determine correlated $\gamma$-ray emissions from nuclear decays. Measured singles and coincidence rates share common factors that can be divided out in the analysis. However, standard formulations often assume perfect correlation between emitted quanta, neglecting possible decay chain losses, and ignore angular correlations. In this work, coincidence-based absolute activity measurements are used to show that the angular correlation function, $W(\theta)$, modulates the detection probability of cascade pairs. Using $^{60}$Co and $^{22}$Na as benchmark sources with differing cascade and correlation properties, measurements with a segmented multi-detector array demonstrate that the true coincidence rate reflects detector efficiencies and angular correlations, which can be extracted from the measured observables.\
To support the interpretation of the measured angular correlations and investigate the impact of detector effects, a custom \texttt{FLUKA} source routine was developed to implement angular distributions in $\gamma-\gamma$ correlations consistent with experimental observations. By implementing the Probability Density Function (PDF) of $W(\theta)$, a normalized Cumulative Distribution Function (CDF) was established. The CDF was then incorporated into the source routine using tabulated values and linear interpolation for precise event sampling. The
Monte Carlo results successfully reproduce the experimentally observed angular modulation, confirming that coincidence counting combined with a tailored simulation framework can probe angular correlations. The approach forms the groundwork for future studies of more complicated decay schemes with non-trivial cascade probabilities and for developing multi-detector techniques for angular-correlation measurements and metrology.
| Apply for student award at which level: | PhD |
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