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

TL;DR

This study presents new high-precision mass measurements of neutron-rich zinc and gallium isotopes, revealing their impact on understanding the formation of the first r-process peak during neutron star mergers.

Contribution

It provides the first mass measurements of $^{83}$Zn and $^{86}$Ga, reducing uncertainties and exploring their influence on r-process abundance patterns in astrophysical models.

Findings

Mass measurements reduce uncertainties in isotopic abundances.

Abundance patterns vary significantly with electron fraction in BNS mergers.

Some abundance patterns match metal-poor stars, others deviate from solar r-process.

Abstract

The prediction of isotopic abundances resulting from the rapid neutron capture process (r-process) requires high-precision mass measurements. Using TITAN's on-line time-of-flight spectrometer, first time mass measurements are performed for $^{83}$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 in abundance across a range of trajectories is found when comparing to several metal-poor stars while also strongly deviating from the solar r-process pattern. These findings point to a high degree of sensitivity to the electron fraction of a BNS merger on the final elemental abundance pattern for certain elements near the first r-process peak while others display universality. We find that small changes in electron fraction can produce distinct abundance patterns that match those of metal-poor stars with different classifications.