Triaxial projected shell model study of $\gamma$-bands in atomic nuclei

TL;DR

This paper uses the triaxial projected shell model to analyze gamma-bands in atomic nuclei, revealing insights into their softness or static deformation, and comparing results with collective model predictions.

Contribution

It applies the TPSM approach to systematically study gamma-bands, including quasiparticle effects, and compares these results with collective model predictions for transition probabilities.

Findings

Most nuclei show gamma-softness with even-I-below-odd-I staggering.

Four nuclei exhibit static gamma-deformation with odd-I-below-even-I staggering.

Quasiparticle excitations can reverse the staggering phase in most studied nuclei.

Abstract

A systematic study of $\gamma$-bands observed in atomic nuclei is performed using the triaxial projected shell model (TPSM) approach. The staggering phase between the even and odd spin members of the $\gamma$-band for most the nuclei investigated in the present work is found to have even-I-below-odd-I, which in the framework of the collective model is considered as a signature of $\gamma$-softness. It is observed that out of twenty-three systems studied, only four nuclei, namely, $^{76}$Ge, $^{112}$Ru, $^{170}$Er and $^{232}$Th depict staggering phase with odd-I-below-even-I, which is regarded as an indication of the static $\gamma$-deformation in the collective model picture. The inclusion of the quasiparticle excitations in the framework of configuration mixing is shown to reverse the staggering phase from odd-I-down to the even-I-down for all the studied nuclei, except for the aforementioned four nuclei. Furthermore, by fitting a collective Bohr Hamiltonian to the TPSM energies, the differences between the two models are delineated through a comparison of the transition probabilities.