Neutron activation of Ga69 and Ga71 at kBT≈25keV

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 ${k}_{\mathrm{B}}T\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}25$ keV is the first experiment in a series of activation and time-of-flight measurements on $^{69}\mathrm{Ga}$ and $^{71}\mathrm{Ga}$ relevant for astrophysics.Methods: We activated $^{69}\mathrm{Ga}$ and $^{71}\mathrm{Ga}$ with a neutron distribution that corresponds to a quasistellar distribution with ${k}_{\mathrm{B}}T=25\phantom{\rule{4pt}{0ex}}\mathrm{keV}$ at the Joint Research Centre (JRC), Geel, Belgium. Protons were provided by an electrostatic Van de Graaff accelerator to produce neutrons via the reaction $^{7}\mathrm{Li}(\mathrm{p},\mathrm{n})$. The produced activity was measured via the $\ensuremath{\gamma}$ 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 ${\ensuremath{\sigma}}_{\text{Ga}}/{\ensuremath{\sigma}}_{\text{Au}}$ for the neutron spectrum of the activation. We obtain values of ${\ensuremath{\sigma}}_{69\mathrm{Ga},\mathrm{SACS}}=(186\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}12)\phantom{\rule{4pt}{0ex}}\mathrm{mb}$ and ${\ensuremath{\sigma}}_{71\mathrm{Ga},\mathrm{SACS}}=(112\phantom{\rule{0.16em}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}7)\phantom{\rule{4pt}{0ex}}\mathrm{mb}$, and cross-section ratios of ${\ensuremath{\sigma}}_{\text{69Ga}}/{\ensuremath{\sigma}}_{\text{Au}}=0.29\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.02$ and ${\ensuremath{\sigma}}_{\text{71Ga}}/{\ensuremath{\sigma}}_{\text{Au}}=0.17\phantom{\rule{4pt}{0ex}}\ifmmode\pm\else\textpm\fi{}\phantom{\rule{0.16em}{0ex}}0.01$.Conclusions: Our data disagree with the available evaluated data provided by KADoNiS v0.3, our cross-section ratio is about 20% higher for $^{69}\mathrm{Ga}$ and about 20% lower for $^{71}\mathrm{Ga}$.