The ${\beta }^{+}$-decay half-lives of the neutron-deficient odd-odd $N=Z$ nuclei ${}^{74}\mathrm{Rb},$ ${}^{78}\mathrm{Y},$ ${}^{82}\mathrm{Nb},$ and ${}^{86}\mathrm{Tc}$ have been measured following the fragmentation of a primary ${}^{92}\mathrm{Mo}$ 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 ${\log }_{10}{\mathrm{ft}}_{1/2}$ values are consistent with $0^{+}\to 0^{+},$ Fermi superallowed transitions, which together with the measured ${\beta }^{+}$-detection efficiencies, suggest $T=1,$ $I^{\pi }{=0\mathrm{}}^{+}$ 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.

• Received 9 June 2000

DOI:https://doi.org/10.1103/PhysRevC.63.044307