Improved $^{192,194,195,196}$Pt($n,\gamma $) and $^{192}$Ir($n,\gamma $) astrophysical reactions rates

TL;DR

This study measured neutron capture cross sections for platinum isotopes to derive accurate astrophysical reaction rates, improving upon previous estimates and aiding in nucleosynthesis modeling.

Contribution

The paper provides the first precise measurements of neutron capture rates for platinum isotopes, refining astrophysical models of the s-process and calibrating nuclear statistical calculations.

Findings

Reaction rates for Pt isotopes are accurate to 3-5%.

New rates differ from previous estimates by up to 35%.

Calibrated models improve understanding of s-process nucleosynthesis.

Abstract

$^{192}$Pt is produced solely by the slow neutron capture (\textit{s}) nucleosynthesis process and hence an accurate ($n$,$\gamma $) reaction rate for this nuclide would allow its use as an important calibration point near the termination of the \textit{s}-process nucleosynthesis flow. For this reason, we have measured neutron capture and total cross sections for $% ^{192,194,195,196,nat}$Pt in the energy range from 10 eV to several hundred keV at the Oak Ridge Electron Linear Accelerator. Measurements on the other Pt isotopes were, in part, necessitated by the fact that only a relatively small $^{192}$Pt sample of modest enrichment was available. Astrophysical $% ^{192,194,195,196}$Pt($n,\gamma $) reaction rates, accurate to approximately 3%--5 %, were calculated from these data. No accurate reaction rates have been published previously for any of these isotopes. At \textit{s}-process temperatures, previously recommended rates are larger (by as much as 35%) and have significantly different shapes as functions of temperature, than our new rates. We used our new Pt results, together with $^{191,193}$Ir(n,$% \gamma $) data, to calibrate nuclear statistical model calculations and hence obtain an improved rate for the unmeasured \textit{s}-process branching-point isotope $^{192}$Ir.