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arXiv · 2505.16515

Seniority-two valence-shell building blocks of the octupole phonon

M. Scheck·R. Chapman·K. Mashtakov·R. Meeten·P. L. Sassarini·P. Spagnoletti
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Abstract

The relative ordering of $J^-$ levels of multiplets resulting from two-body excitations, which include a $J^{\pi}=3^-$ state that can contribute to the octupole phonon, are investigated in a simplistic shell-model approach. To calculate the relative level ordering, harmonic oscillator wavefunctions and a residual $\delta$ interaction are used. The simplistic approach confirms for the particle-particle channel, the often stated preference of the $\Delta j=3, \Delta l =3$ subshell combination over the $\Delta j=3, \Delta l =1$ subshell combination through an enhanced energy gain. Furthermore, it is shown that, in the particle-hole channel, the gain is less pronounced for the $\Delta j=3, \Delta l =3$ subshell configuration. In combination with the overall structure of an oscillator shell, these results explain the comparatively low excitation energy for 3$^-_1$ excitations observed for the octupole-soft proton and neutron numbers predicted by various models.

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M. Scheck, R. Chapman, K. Mashtakov, R. Meeten, P. L. Sassarini, P. Spagnoletti. 2025-05-22. Seniority-two valence-shell building blocks of the octupole phonon. https://arxiv.org/abs/2505.16515

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