Shape coexistence in 71Br and the question of the ground-state spin of 71Kr -: art. no. 024321

When the N=Z line approaches the proton dripline above Ni-56 an increasing distortion of mirror symmetry is expected as the proton-rich partner becomes marginally bound. Urkedal and Hamamoto have considered Kr-71 and suggest the distortion could lead to a different ground-state spin to its mirror partner Br-71, based on the reinterpretation of a beta-decay measurement. This would be a unique situation in T=1/2 nuclei. We have performed a new in-beam spectroscopic measurement of Br-71, following the Ca-40(Ca-40,2 alpha p) reaction at 160 MeV and using Gammasphere. Many new states have been found, with candidates for eight Nilsson bandheads below 1 MeV. Cross-linking decays tightly constrain most of the angular momentum assignments. The Kr-71 beta-decay data, seen in the light of this new information on Br-71, support the original ground-state assignment of Kr-71 as J(pi)=5/2(-), as would be normally expected for the mirror partner of J(pi)=5/2(-) Br-71.