Triaxial projected shell model study of γ-bands in atomic nuclei

A systematic study of γ -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 γ -band for most of 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 γ -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 γ -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.