Stellar neutron capture cross sections of the tin isotopes

Abstract

The neutron capture cross sections of ${}_{}{}^{114}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{115}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{116}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{117}{}_{}{}^{}\mathrm{Sn}$, ${}_{}{}^{118}{}_{}{}^{}\mathrm{Sn}$, and ${}_{}{}^{120}{}_{}{}^{}\mathrm{Sn}$ were measured in the energy range from 3 to 225 keV at the Karlsruhe 3.75 MV Van de Graaff accelerator. Neutrons were produced via the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$(p,n${)}^7$Be reaction using a pulsed proton beam. Capture events were registered with the Karlsruhe 4π barium fluoride detector. The experiment was complicated by the small (n,γ) cross sections of the proton magic tin isotopes and by the comparably low enrichment of the rare isotopes ${}_{}{}^{114}{}_{}{}^{}\mathrm{Sn}$ and ${}_{}{}^{115}{}_{}{}^{}\mathrm{Sn}$. Despite significant corrections for capture of scattered neutrons and for isotopic impurities, the high efficiency and the spectroscopic quality of the ${\mathrm{BaF}}_2$ detector allowed the determination of the cross-section ratios with overall uncertainties of 1–2 %, five times smaller compared to existing data. Based on these results, Maxwellian averaged (n,γ) cross sections were calculated for thermal energies between kT=10 and 100 keV. These data are used for a discussion of the solar tin abundance and for an improved determination of the isotopic s- and r-process components. © 1996 The American Physical Society.