Half-life measurements forGa61,Ge63, andAs65and their importance in therpprocess

The rp process provides a mechanism whereby energy is generated and proton-rich nuclei are synthesized in various astrophysical environments. Understanding this process requires knowledge of the half-lives, binding energies, and reaction cross sections for the nuclei along its path, which for A≳60 lies near the proton-drip line. Using the A1200 radioactive-beam facility at the National Superconducting Cyclotron Laboratory, we have performed an experiment to measure the β-decay half-lives of several ${\mathit{T}}_{\mathit{z}}$=-1/2 nuclei in this mass region by identification and implantation of projectile fragments followed by a rapid beam cutoff and observation of the β decay. Using this technique, the half-lives of ${}_{}{}^{61}{}_{}{}^{}\mathrm{Ga}$, ${}_{}{}^{63}{}_{}{}^{}\mathrm{Ge}$, and ${}_{}{}^{65}{}_{}{}^{}\mathrm{As}$ (0.15±0.03 s, ${95}_{\mathrm{-}20}^{+23\mathrm{}}$ ms, and 0.${19}_{\mathrm{-}0.07}^{+0.11\mathrm{}}$ s, respectively) have been measured and are found to be consistent with expectations from β-decay theory for decay between mirror states with ${\mathit{Q}}_{\mathrm{\beta }}$∼9 MeV. In addition, the proton-rich nucleus ${}_{}{}^{66}{}_{}{}^{}\mathrm{Se}$ has been observed for the first time. The experimental method used for this measurement and the implications of these results for the rp process are discussed.