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

Abstract

The ${\beta }^{-}$ 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 $\gamma$ spectroscopy. The ${}^{81}$Zn half-life was determined to be $T_{1/2}=290(4)$ ms while the $\beta$-delayed neutron emission probability was measured as $P_n=23(4)\%$. The analysis of the $\beta$-gated $\gamma$-ray singles and $\gamma$-$\gamma$ coincidences from the decay of ${}^{81}$Zn provides 47 new levels and 70 new transitions in ${}^{81}$Ga. The ${\beta }^{-}$$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.

arXiv commentSubmitted to Phys. Rev. C

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