Nature of γ deformation in Ge and Se nuclei and the triaxial projected shell model description

Recent experimental data have demonstrated that Ge-76 may be a rare example of a nucleus exhibiting rigid gamma deformation in the low-spin regime. In the present work, the experimental analysis is supported by microscopic calculations using the multi-quasiparticle triaxial projected shell model (TPSM) approach. It is shown that to best describe the data of both yrast and gamma-vibrational bands in Ge-76, a rigid-triaxial deformation parameter gamma approximate to 30 degrees is required. TPSM calculations are discussed in conjunction with the experimental observations and also with the published results from the spherical shell model. The occurrence of a gamma gamma band in Ge-76 is predicted with the bandhead at an excitation energy of similar to 2.5 MeV. We have also performed TPSM study for the neighboring Ge and Se isotopes and the distinct gamma-soft feature in these nuclei is shown to result from configuration mixing of the ground-state with multi-quasiparticle states.