Neutron activation of $^{69}$Ga and $^{71}$Ga at kBT≈25 keV

Abstract

Background: About 50% of heavy elements are produced by the slow neutron capture process (s process) in stars. The element gallium is mostly produced during the weak s process in massive stars. Purpose: Our activation at k$_{B}$T≈25 keV is the first experiment in a series of activation and time-of-flight measurements on $^{69}$Ga and $^{71}$Ga relevant for astrophysics. Methods: We activated $^{69}$Ga and $^{71}$Ga with a neutron distribution that corresponds to a quasistellar distribution with k$_{B}$T=25 keV at the Joint Research Centre (JRC), Geel, Belgium. Protons were provided by an electrostatic Van de Graaff accelerator to produce neutrons via the reaction $^{7}$Li(p,n). The produced activity was measured via the γ emission by the decaying product nuclei by high-purity germanium detectors. Results: We provide spectrum-averaged cross sections (SACS) and ratios of the cross sections σ$_{Ga}$/σ$_{Au}$ for the neutron spectrum of the activation. We obtain values of σ$_{69Ga,SACS}$=(186±12) mb and σ$_{71GA,SACS}$ = (112±7) mb, and cross section ratios of σ$_{69Ga}$/σ$_{Au}$=0.29±0.02 and σ$_{71Ga}$/σ$_{Au}$ = 0.17±0.01. Conclusions: Our data disagree with the available evaluated data provided by KADoNiS v0.3, our cross-section ratio is about 20% higher for $^{69}$Ga and about 20% lower for $^{71}$Ga