SAIP2026

Electric Quadrupole Matrix Elements Supports Triaxial Rotation in Semimagic 60Ni

9 Jul 2026, 11:40

20m

Lecture Hall GH2 (University of the Western Cape)

Oral Presentation Track B - Nuclear, Particle and Radiation Physics Nuclear, Particle and Radiation Physics -1

Speaker

Andile Zulu (University of the Western Cape)

Description

Low-energy Coulomb-excitation (reorientation-effect) measurements [1] of the first excited $2_1^+$ state in $^{60}$Ni were performed at iThemba LABS using the $^{194}$Pt($^{60}$Ni,$^{60}$Ni)$^{194}$Pt reaction at $T_{\mathrm{lab}} = 242.7$ MeV. Previous Coulomb-excitation measurements at iThemba LABS have been performed for $^{20}$Ne [2] and $^{36}$Ar [3]. A diagonal electric quadrupole matrix element of $\langle 2_1^+ | \hat{E2} | 2_1^+ \rangle = +0.10(2)$ eb was determined, corresponding to a spectroscopic quadrupole moment of $Q_s(2_1^+) = +0.08(1)$ eb. This value differs from the evaluated NNDC value of $+0.03(5)$ eb and is inconsistent with the negative quadrupole moment extracted from electron scattering measurements and reported in Stone's 2021 evaluation [4]. The positive quadrupole moment indicates an oblate deformation, in contrast to the zero quadrupole moment expected for a harmonic vibrator with magic $Z=28$. These results, together with previous evidence for multi-phonon excitations in $^{60}$Ni [5], suggest deviations from a purely vibrational description. Interpreting the measured quadrupole observables within the empirically validated triaxial rotor model [6,7] yields a triaxial deformation parameter of $\gamma = 31.9(4)^\circ$, indicating triaxial rotation.

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triaxial rotation in semi-magic 60Ni. Submitted to PRL.