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

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.

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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.