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 4\ensuremath{\pi} barium fluoride detector. The experiment was complicated by the small (n,\ensuremath{\gamma}) 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,\ensuremath{\gamma}) 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. \textcopyright{} 1996 The American Physical Society.