Fast-timing study of ^81Ga from the β decay of ^81Zn

The β^- decay of ^81Zn to the neutron magic N=50 nucleus ^81Ga, with only three valence protons with respect to ^78Ni, was investigated. The study was performed at the ISOLDE facility at CERN by means of γ spectroscopy. The ^81Zn 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 ^81Zn provides 47 new levels and 70 new transitions in ^81Ga. The β^-n decay of ^81Zn was observed and a new decay scheme into the odd-odd ^80Ga nucleus was established. The half-lives of the first and second excited states of ^81Ga 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 ^81Ga is interpreted in terms of the coupling of the three valence protons outside the doubly-magic ^78Ni core.