Fast-timing study of Ga81 from the β decay of Zn81

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 γ spectroscopy. The 81 Zn half-life was determined to be T 1/2 = 290(4) ms while the β-delayed neutron emission probability was measured as P n = 23(4)%. The analysis of the β-gated γ -ray singles and γ -γ 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.