Mass measurements of ${}^{60-63}$Ga reduce x-ray burst model uncertainties and extend the evaluated $T=1$ isobaric multiplet mass equation

Abstract

We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of ${}^{60-63}$Ga performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of ${}^{61}$Ga and mark the first direct mass measurement of ${}^{60}$Ga. The improved precision of the ${}^{61}$Ga mass has important implications for the astrophysical rp process, as it constrains essential reaction Q-values near the ${}^{60}$Zn waiting point. Based on calculations with a one-zone model, we demonstrate the impact of the improved mass data on prediction uncertainties of X-ray burst models. The first-time measurement of the ${}^{60}$Ga ground-state mass establishes the proton-bound nature of this nuclide; thus, constraining the location of the proton drip line along this isotopic chain. Including the measured mass of ${}^{60}$Ga further enables us to extend the evaluated $T=1$ isobaric multiplet mass equation up to $A=60$.

16 pages, 6 figures