Simultaneous impacts of nuclear shell structure and collectivity on ${\hat{I}}^2$ decay: Evidence from ${}^{80}$Ga${}_{49}$

Abstract

The Gamow-Teller strength distribution covering the entire ${\hat{I}}^2$-decay window, up to 10.312(4) MeV, of ${}^{80g+m}$Ga was measured for the first time in photo fission of UC${}_x$ induced by a 50 MeV electron beam. The new data show significant enhancement in the high-energy region with a jump structure. Simultaneously, the ${\hat{I}}^3$ deexciting behavior of ${\hat{I}}^2$-populated states presents a competition between deexcitation to 2${}_1^{+}$ [${\hat{I}}_2^2$ = 0.155(9)] and to 2${}_2^{+}$ [${\hat{I}}_2^2$ = 0.053${}_{0.009}^{0.008}$)] in ${}^{80}$Ge. To understand these data, we performed a realistic shell-model calculation and systematic analysis of log $ft$ ratios between precursors' ${\hat{I}}^2$ decay to 2${}_2^{+}$ and to 2${}_1^{+}$ of Ga isotopes. We conclude that these phenomena evidence simultaneous impacts of nuclear shell structure and collectivity on $B$(GT) distribution and therefore the half-life of the precursor.