High-Resolution neutron capture and total cross section measurements for ^{192, 194, 195, 196}pt and the astrophysical rates for the ^{192, 194, 195, 196}Pt(n, γ) Reactions

We have made the first experimental determinations of the astrophysical rates for the ^{192, 194, 195, 196}Pt(n, γ) reactions across the range of temperatures needed for astrophysical models of the s process. Both neutron capture and total cross sections were measured for ^{192, 194, 195, 196}Pt at the Oak Ridge Electron Linear Accelerator (ORELA) from 10 eV to 500 keV. The data were fitted using the R-matrix code SAMMY to obtain resonance parameters. These parameters as well as the measured cross sections in the unresolved region were used to obtain the astrophysical reaction rates for all these isotopes. We compare our results to previous data and theoretical reaction rates and discuss their astrophysical impact. For example, a classical analysis of the s-process branching at ¹⁹²Ir using our new rates yields a much lower neutron density than previous analyses of other branchings, in agreement with the long-sought freeze-out effect predicted by dynamical (e.g. stellar) models.