Medium-spin states of the neutron-rich nucleus Br 87

Abstract

Medium-spin excited states of the neutron-rich nucleus Br87 were observed and studied for the first time. They were populated in fission of U235 induced by the cold-neutron beam of the PF1B facility of the Institut Laue-Langevin, Grenoble. The measurement of γ radiation following fission was performed using the EXILL array of Ge detectors. The observed level scheme was compared with results of large valence space shell model calculations. The medium-spin level scheme consists of three bandlike structures, which can be understood as bands built on the πf5/2, π(p3/2+f5/2), and πg9/2 configurations. The behavior of the observed πg9/2 band at high spins shows a considerable deviation from the shell model predictions. This deviation in this band is probably the result of an increased collectivity, which can be understood assuming that the πg9/2 high-j proton polarizes the core.