Mass Measurements of Neutron-Rich Gallium Isotopes Refine Production of Nuclei of the First r-Process Abundance Peak in Neutron Star Merger Calculations

TL;DR

This study provides new mass measurements of neutron-rich gallium isotopes, refining models of element formation in neutron star mergers and confirming their role in producing the first r-process abundance peak.

Contribution

First measurements of $^{84}$Ga and $^{85}$Ga masses, reducing uncertainties in r-process nucleosynthesis models for neutron star mergers.

Findings

Mass measurements of $^{84}$Ga and $^{85}$Ga for the first time.

Refined nuclear data reduces uncertainties in astrophysical r-process simulations.

Simulations support neutron star mergers as sources of the first r-process peak.

Abstract

We report mass measurements of neutron-rich Ga isotopes $^{80-85}$Ga with TRIUMF's Ion Trap for Atomic and Nuclear science (TITAN). The measurements determine the masses of $^{80-83}$Ga in good agreement with previous measurements. The masses of $^{84}$Ga and $^{85}$Ga were measured for the first time. Uncertainties between $25-48$ keV were reached. The new mass values reduce the nuclear uncertainties associated with the production of A $\approx$ 84 isotopes by the \emph{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 $Y_e=0.35-0.38$.