Microscopic investigation of the $I^π=8^-$ isomer decay in even-even N = 74 isotones
The microscopic approach of the triaxial projected shell model (TPSM) is employed to investigate the properties of the $8^-$ isomer in the six isotones of $^{128}$Xe, $^{130}$Ba, $^{132}$Ce, $^{134}$Nd, $^{136}$Sm, and $^{138}$Gd. The observed decay pattern of the isomer for these isotones is unexpected with the hindrance factor decreasing with atomic number. It is shown in the present work that multi-quasiparticle mixing into the ground-state configuration is responsible for the observed decreasing trend of the hindrance factor. We have also calculated the excitation energies and in-band $B(E2)$ transition probabilities of the yrast and the band built on the $8^-$ isomer for the six isotones, and it is shown that TPSM approach reproduces the measured quantities quite satisfactorily.