Triaxial projected shell model approach for negative parity states in even-even nuclei

TL;DR

This paper extends the triaxial projected shell model to include negative parity states in even-even nuclei by allowing quasiparticles to occupy two shells, successfully explaining high-spin band structures in Ru isotopes.

Contribution

The authors develop an extended TPSM approach that incorporates negative parity states by enabling quasiparticle excitations across two shells, a significant advancement over previous models.

Findings

Successfully modeled negative parity high-spin bands in Ru isotopes.

Neutron excitations yield slightly lower energies than proton excitations.

Transition quadrupole moments show rapid changes at band crossings.

Abstract

The triaxial projected shell model (TPSM) approach is generalized to investigate the negative parity band structures in even-even systems. In the earlier version of the TPSM approach, the quasiparticle excitations were restricted to one major oscillator shell and it was possible to study only positive parity states in even-even systems. In the present extension, the excited quasiparticles are allowed to occupy two major oscillator shells, which makes it possible to generate the negative parity states. As a major application of this development, the extended approach is applied to elucidate the negative parity high-spin band structures in $^{102-112}$Ru and it is shown that energies obtained with neutron excitation are slightly lower than the energies calculated with proton excitation. However, the calculated aligned angular momentum ($i_x$) clearly separates the two spectra with neutron $i_x$ in reasonable agreement with the empirically evaluated $i_x$ from the experimental data, whereas proton $i_x$ shows large deviations. Furthermore, we have also deduced the transition quadrupole moments from the TPSM wavefunctions along the negative-parity yrast- and yrare- bands and it is shown that these quantities exhibit rapid changes in the bandcrossing region.