Shape coexistence in Br71 and the question of the ground-state spin of Kr71

When the N=Z line approaches the proton dripline above Ni56 an increasing distortion of mirror symmetry is expected as the proton-rich partner becomes marginally bound. Urkedal and Hamamoto have considered Kr71 and suggest the distortion could lead to a different ground-state spin to its mirror partner Br71, based on the reinterpretation of a β-decay measurement. This would be a unique situation in T=1/2 nuclei. We have performed a new in-beam spectroscopic measurement of Br71, following the Ca40(Ca40,2αp) 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 Kr71 β-decay data, seen in the light of this new information on Br71, support the original ground-state assignment of Kr71 as Jπ=5/2-, as would be normally expected for the mirror partner of Jπ=5/2- Br71.