Fast-timing study of ${}^{81}$Ga from the ${\hat{I}}^2$ decay of ${}^{81}$Zn

Abstract

The $β^{-}$ decay of ${}^{81}$Zn to the neutron magic $N=50$ nucleus ${}^{81}$Ga, with only three valence protons with respect to ${}^{78}$Ni, was investigated. The study was performed at the ISOLDE facility at CERN by means of ${\hat{I}}^3$ spectroscopy. The ${}^{81}$Zn half-life was determined to be $T_{1/2}=290(4)$ ms while the ${\hat{I}}^2$-delayed neutron emission probability was measured as $P_n=23(4)\%$. The analysis of the ${\hat{I}}^2$-gated ${\hat{I}}^3$-ray singles and ${\hat{I}}^3$-${\hat{I}}^3$ coincidences from the decay of ${}^{81}$Zn provides 47 new levels and 70 new transitions in ${}^{81}$Ga. The $β^-$$n$ decay of ${}^{81}$Zn was observed and a new decay scheme into the odd-odd ${}^{80}$Ga nucleus was established. The half-lives of the first and second excited states of ${}^{81}$Ga were measured via the fast-timing method using LaBr${}_3$(Ce) detectors. The level scheme and transition rates are compared to large-scale shell-model calculations. The low-lying structure of ${}^{81}$Ga is interpreted in terms of the coupling of the three valence protons outside the doubly-magic ${}^{78}$Ni core.

Submitted to Phys. Rev. C