Fermi superallowed β⁺ decays and T=1 ground states of heavy odd-odd N=Z nuclei

The β+-decay half-lives of the neutron-deficient odd-odd N=Z nuclei 74Rb, 78Y, 82Nb, and 86Tc have been measured following the fragmentation of a primary 92Mo beam at an energy of 60 MeV per nucleon at the GANIL laboratory, France. This was achieved by correlating β+ decays with the implantation of unambiguously identified fragments at the final focus of the LISE3 separator. The deduced log10 ft1/2 values are consistent with 0+→0+, Fermi superallowed transitions, which together with the measured β+-detection efficiencies, suggest T=1, Iπ=0+ ground states for these odd-odd N=Z nuclei. These data represent the heaviest N=Z systems for which Fermi superallowed decays have been established.