High-resolution neutron capture and transmission measurements for 116,120Sn, and their stellar neutron-capture cross sections at s-process temperatures

Details High-resolution neutron capture and transmission measurements for 116,120Sn, and their stellar neutron-capture cross sections at s-process temperatures High-resolution neutron capture and transmission measurements for 116,120Sn, and their stellar neutron-capture cross sections at s-process temperatures

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phrvc..64f5802k&link_type=abstract

Physical Review C (Nuclear Physics), Volume 64, Issue 6, December 2001, p.065802

Physics

Nuclear Physics

4

Hydrostatic Stellar Nucleosynthesis

Scientific paper

We have made high-resolution measurements of the neutron capture and total cross sections for 116Sn and the neutron capture cross section for 120Sn from 50 eV to 500 keV at the Oak Ridge Electron Linear Accelerator (ORELA). There have been no previously reported high-resolution measurements of these cross sections in this energy range. We performed an R-matrix analysis of our new data as well as previous total cross section data for 120Sn to extract parameters for 216 resonances in 117Sn between 100 eV and 30 keV, and 187 resonances in 121Sn between 350 eV and 55 keV. These resonance parameters were used to calculate the average radiation widths, average level spacings, and strength functions for s- and p-wave neutron resonances. The 116,120Sn(n,γ) astrophysical reaction rates were determined, to approximately 3% accuracy across the entire range of temperatures needed by the latest stellar models of the s process, from these resonance parameters together with our neutron capture measurements in the unresolved region. At the canonical s-process temperature of kT=30 keV, our 116Sn(n,γ) rate agrees to within the experimental uncertainties with the most recent high-precision measurement, and our 120Sn(n,γ) rate resolves the discrepancy between two recent high-precision measurements. However, our measurements show that the most recently recommended reaction rates (which are based on extrapolations from previous measurements at higher energies) at kT=6-8 keV, where most of the neutron exposure occurs in stellar s-process models, are too high by approximately 10-20 %. We discuss the astrophysical impact of our new rates.

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