Half-lives of Sr73 and Y76 and the consequences for the proton dripline

Abstract

The half-lives of seven nuclei have been determined in the neutron-deficient mass-70 region following their production via fragmentation of a 345 MeV/nucleon ${}^{124}\mathrm{Xe}$ primary beam on a 740 mg/${\mathrm{cm}}^2 {}^9\mathrm{Be}$ target at the RI Beam Factory, RIKEN. The results include two new (${}^{73}\mathrm{Sr}$ and ${}^{76}\mathrm{Y}$) half-lives and a more precise measurement for the ground-state half-life of ${}^{74}\mathrm{Sr}$. The new results are discussed with reference to previously published calculations that predict the location of the proton dripline in the light Sr and Y region of the nuclear chart. In addition, differences in the ground-state structure of ${}^{72}\mathrm{Rb}$ and ${}^{76}\mathrm{Y}$ are discussed with the aid of density functional theory calculations. These provide a possible explanation for why ${}^{72}\mathrm{Rb}$ undergoes proton decay while the $\alpha$-conjugate nucleus ${}^{76}\mathrm{Y}$ predominantly undergoes ${\beta }^{+}$ decay.