Direct mass measurements of neutron-rich zinc and gallium isotopes: an investigation of the formation of the first r-process peak

The prediction of isotopic abundances resulting from the rapid neutron capture process (r-process) requires high-precision mass measurements. Mass measurements of \(^{79-83}\)Zn and \(^{85,86}\)Ga using TITAN's on-line time-of-flight spectrometer. First time measurements are performed for \(^{79m}\)Zn, \(^{83}\)Zn, and \(^{86}\)Ga. These measurements reduced uncertainties, and are used to calculate isotopic abundances near the first r-process abundance peak using astrophysical conditions present during a binary neutron star (BNS) merger. Good agreement across a range of trajectories is found when comparing to several metal-poor stellar abundances. Particularly, this subset of trajectories produces agreement with the abundance pattern of both the `r/s-star' HD94028 as well as the `r-process star' HD222925. These findings point to a high degree of sensitivity to the electron fraction of a BNS merger on the final elemental abundance pattern near the first r-process peak. In particular, we find that small changes in electron fraction produce distinct abundance patterns that match those of metal-poor stars with different classifications, calls the need for an i-process into question.