Stellar neutron capture cross sections of the tin isotopes

The neutron capture cross sections of ¹¹⁴Sn, ¹¹⁵Sn, ¹¹⁶Sn, ¹¹⁷Sn, ¹¹⁸Sn, and ¹²⁰Sn 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 ⁷Li(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 ¹¹⁴Sn and ¹¹⁵Sn. Despite significant corrections for capture of scattered neutrons and for isotopic impurities, the high efficiency and the spectroscopic quality of the BaF₂ 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.