Mass measurements of neutron-rich gallium isotopes refine production of nuclei of the first r -process abundance peak in neutron-star merger calculations

We report mass measurements of neutron-rich Ga isotopes ^Ga-85₈₀ with TRIUMF's Ion Trap for Atomic and Nuclear science. The measurements determine the masses of ^Ga-83₈₀ in good agreement with previous measurements. The masses of ⁸⁴Ga and ⁸⁵Ga were measured for the first time. Uncertainties between 25 and 48 keV were reached. The new mass values reduce the nuclear uncertainties associated with the production of A ≈84 isotopes by the r -process for astrophysical conditions that might be consistent with a binary neutron star (BNS) merger producing a blue kilonova. Our nucleosynthesis simulations confirm that BNS merger may contribute to the first abundance peak under moderate neutron-rich conditions with electron fractions Y_e=0.35 -0.38 .