Low-spin excitations in Br89 populated in β− decay of Se89

Abstract

Low-spin, excited states of the $^{89}\mathrm{Br}$ nucleus, populated in ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{89}\mathrm{Se}$ have been studied for the first time. The $^{89}\mathrm{Se}$ 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 ${\ensuremath{\beta}}^{\ensuremath{-}}$ decay of $^{89}\mathrm{Se}$ was measured with an array of high-resolution germanium detectors. Levels scheme of $^{89}\mathrm{Br}$ was extended by 12 new levels and 31 new $\ensuremath{\gamma}$ transitions. Spin-parity (3/${2}^{+}$) has been proposed for the ground state of the $^{89}\mathrm{Se}$ mother nucleus, replacing the (5/${2}^{+}$) assignment reported in data bases. The observed Gamow-Teller ${\ensuremath{\beta}}^{\ensuremath{-}}$ transition to the 1754.5-keV level indicates a $\ensuremath{\pi}{g}_{9/2}$-based configuration. The level scheme of $^{89}\mathrm{Br}$ has been compared to large scale shell-model calculations. Excitations based on $\ensuremath{\pi}{p}_{3/2}$ and $\ensuremath{\pi}{f}_{5/2}$ single-particle levels as well as their anomalous coupling are proposed to explain the low-energy excitation scheme of $^{89}\mathrm{Br}$.