Nature ofγdeformation in Ge and Se nuclei and the triaxial projected shell model description

Abstract

Recent experimental data have demonstrated that ${}^{76}$Ge may be a rare example of a nucleus exhibiting rigid $\ensuremath{\gamma}$ 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 $\ensuremath{\gamma}$-vibrational bands in ${}^{76}$Ge, a rigid-triaxial deformation parameter $\ensuremath{\gamma}\ensuremath{\approx}{30}^{\ensuremath{\circ}}$ 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 $\ensuremath{\gamma}\ensuremath{\gamma}$ band in ${}^{76}$Ge is predicted with the bandhead at an excitation energy of $\ensuremath{\sim}$2.5 MeV. We have also performed TPSM study for the neighboring Ge and Se isotopes and the distinct $\ensuremath{\gamma}$-soft feature in these nuclei is shown to result from configuration mixing of the ground-state with multi-quasiparticle states.