Evidence for shape coexistence in 77Br Original Research Article

The nucleus 77Br has been studied in the reaction 65Cu(16O, 2p2n) at E=75 MeV. Lifetimes have been measured for several states using the Doppler-shift attenuation technique. The B(E2) values for the inband transitions, deduced from the lifetime results, reflect strong collectivity for both the positive-parity yrast band (band 1) and the ground-state negative-parity band (band 2). States with spin above 17/2+ in band 1 are found to have a large average quadrupole deformation of β2=0.35. The experimental results for band 2 suggest that the 25/2− and 29/2− states are somewhat more strongly deformed than the lower-spin states. A comparison of the experimental results with particle-rotor-model calculations provides evidence for shape coexistence in 77Br, favouring a prolate shape for the g9/2 yrast band and an oblate shape for the lowest negative-parity band.