Fri·May 23, 2025Friday·May 23, 2025

1. 01*

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

   M. Scheck🇬🇧 · R. Chapman · K. Mashtakov · R. Meeten · P.L. Sassarini · P. Spagnoletti🇨🇦

   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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* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.