Fermi superallowed β+ decays and T=1 ground states of heavy odd-odd N=Z nuclei -: art. no. 044307

The beta (+) -decay half-lives of the neutron-deficient odd-odd N=Z nuclei Rb-74, Y-78, Nb-82, and Tc-86 have been measured following the fragmentation of a primary Mo-92 beam at an energy of 60 MeV per nucleon at the GANIL laboratory, France. This was achieved by correlating beta (+) decays with the implantation of unambiguously identified fragments at the final focus of the LISE3 separator. The deduced log(10)ft(1/2) values are consistent with 0(+)-->0(+). Fermi superallowed transitions, which together with the measured beta (+)-detection efficiencies, suggest T=1, I-pi=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.