Excited states in 87Br populated in β decay of 87Se

Abstract

Excited levels in 87Br, populated in β decay of 87Se, have been studied by means of γ-ray spectroscopy using an array of broad energy Ge detectors. 87Se nuclei were produced by irradiating a natural Th target with 25-MeV protons. Fission products were extracted from the target chamber using the IGISOL technique, then separated on a dipole magnet and Penning trap (JYFLTRAP) setup. The scheme of excited levels of 87Br has been significantly extended. 114 new transitions and 51 new levels were established. β feedings and log(ft) values of levels were determined. The upper limit for β feeding to the ground state of 87Br was determined to be 23(5)%. Ground state spin and parity 5/2− was confirmed, as suggested by previous studies. We also confirm the low-energy excited state at 6.02 keV. The ground state and two lowest excited states in 87Br were interpreted as the (πf5/2)3j,j−1,j−2 triplet produced by the so-called anomalous coupling. The 333.61- and 699.26-keV levels were interpreted as πp3/2 and πp1/2 single-particle excitations. The 9/2+ level reported previously as corresponding to the πg9/2 single-particle excitation is proposed to be an isomer with half-life 20 ns. Large-scale shell-model calculations performed in this work are in good agreement with experimental results.