Low-spin excitations in Br-89 populated in beta(-) decay of Se-89

Low-spin, excited states of the Br-89 nucleus, populated in beta(-)decay of Se-89 have been studied for the first time. The Se-89 nuclei were produced in proton-induced fission of natural thorium using the IGISOL facility and separated using a dipole magnet and the coupled JYFLTRAP Penning trap. Gamma radiation following the beta(-) decay of Se-89 was measured with an array of high-resolution germanium detectors. Levels scheme of Br-89 was extended by 12 new levels and 31 new gamma transitions. Spin-parity (3/2(+)) has been proposed for the ground state of the Se-89 mother nucleus, replacing the (5/2(+)) assignment reported in data bases. The observed Gamow-Teller beta(-) transition to the 1754.5-keV level indicates a pi g(9/2)-based configuration. The level scheme of Br-89 has been compared to large scale shell-model calculations. Excitations based on pi p(3/2) and pi f(5/2) single-particle levels as well as their anomalous coupling are proposed to explain the low-energy excitation scheme of Br-89.