Medium-Spin States Of The Neutron-Rich Nucleus Br-87

Medium-spin excited states of the neutron-rich nucleus Br-87 were observed and studied for the first time. They were populated in fission of U-235 induced by the cold-neutron beam of the PF1B facility of the Institut Laue-Langevin, Grenoble. The measurement of gamma 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 pi f(5/2), pi(p(3/2) + f(5/2)), and pi g(9/2) configurations. The behavior of the observed pi g(9/2) 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 pi g(9/2) high-j proton polarizes the core.