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

TL;DR

This study investigates the beta decay of $^{81}$Zn to $^{81}$Ga, revealing new nuclear levels and transitions, measuring half-lives, and comparing results with shell-model calculations to understand nuclear structure near $^{78}$Ni.

Contribution

It provides the first detailed level scheme of $^{81}$Ga from $^{81}$Zn decay, including new levels, transitions, and decay pathways, with experimental data supporting shell-model interpretations.

Findings

Measured $^{81}$Zn half-life as 290 ms.

Identified 47 new levels and 70 new transitions in $^{81}$Ga.

Observed beta-delayed neutron emission and established a new decay scheme.

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.