Mass measurements of neutron-rich gallium isotopes refine production of nuclei of the first <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>r</mml:mi></mml:math>-process abundance peak in neutron-star merger calculations

Abstract

We report mass measurements of neutron-rich Ga isotopes $^{80\ensuremath{-}85}\mathrm{Ga}$ with TRIUMF's Ion Trap for Atomic and Nuclear science. The measurements determine the masses of $^{80\ensuremath{-}83}\mathrm{Ga}$ in good agreement with previous measurements. The masses of $^{84}\mathrm{Ga}$ and $^{85}\mathrm{Ga}$ 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 $A\ensuremath{\approx}84$ 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 ${Y}_{e}=0.35\ensuremath{-}0.38$.