Stellar $s$-process neutron capture cross sections of $^{69,71}$Ga

TL;DR

This study measures neutron capture cross sections of gallium isotopes relevant to stellar nucleosynthesis, providing data that aligns with previous results and enhances understanding of the weak s-process in massive stars.

Contribution

The paper presents new experimental measurements of neutron capture cross sections for $^{69}$Ga and $^{71}$Ga using a high-intensity neutron beam, closely simulating stellar conditions.

Findings

Measured Maxwellian-averaged cross sections at 30 keV: 136(8) mb for $^{69}$Ga and 105(7) mb for $^{71}$Ga.

Results are consistent with previous experimental data.

Implications for stellar nucleosynthesis models are discussed.

Abstract

The stable gallium isotopes, $^{69,71}$Ga, are mostly produced by the weak slow ($s$) process in massive stars. We report here on measurements of astrophysically-relevant neutron capture cross sections of the $^{69,71}$Ga$(n,\gamma)$ reactions. The experiments were performed by the activation technique using a high-intensity ($3-5\times10^{10}$ n/s), quasi-Maxwellian neutron beam that closely mimics conditions of stellar $s$-process nucleosynthesis at $kT \approx$ 40 keV. The neutron field was produced by a mA proton beam at $E_p=1925$ keV (beam power of 2-3 kW) from the Soreq Applied Research Accelerator Facility (SARAF), bombarding the Liquid-Lithium Target (LiLiT). A 473 mg sample of Ga$_2$O$_3$ of natural isotopic composition was activated in the LiLiT neutron field and the activities of $^{70,72}$Ga were measured by decay counting via $\gamma$-spectrometry with a high-purity germanium detector. The Maxwellian-averaged cross sections at $kT$ = 30 keV of $^{69}$Ga and $^{71}$Ga determined in this work are 136(8) mb and 105(7) mb, respectively, in good agreement with previous experimental values. Astrophysical implications of the measurements are discussed.