Mass measurements of Ga60-63 reduce x-ray burst model uncertainties and extend the evaluated T=1 isobaric multiplet mass equation

We report precision mass measurements of neutron-deficient gallium isotopes approaching the proton drip line. The measurements of Ga60-63 performed with the TITAN multiple-reflection time-of-flight mass spectrometer provide a more than threefold improvement over the current literature mass uncertainty of Ga-61 and mark the first direct mass measurement of Ga-60. The improved precision of the Ga-61 mass has important implications for the astrophysical rp process, as it constrains essential reaction Q values near the Zn-60 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 Ga-60 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 Ga-60 further enables us to extend the evaluated T = 1 isobaric multiplet mass equation up to A = 60.