Re-evaluation of the $^{16}$O($n$,$\gamma$)$^{17}$O cross section at astrophysical energies and its role as neutron poison in the $s$ process

TL;DR

This study re-evaluates the neutron capture cross section of $^{16}$O at astrophysical energies, providing updated Maxwellian-averaged cross sections that influence models of the s-process in stellar environments.

Contribution

It offers a new, more accurate set of cross sections for $^{16}$O(n,γ)$^{17}$O, impacting astrophysical models of neutron capture processes.

Findings

New MACS values are lower up to 60 keV and up to 14% higher at 100 keV.

Revised cross sections affect the understanding of neutron poisoning in the s-process.

Impact on stellar nucleosynthesis models during core helium and shell carbon burning.

Abstract

The doubly-magic nucleus $^{16}$O has a small neutron capture cross section of just a few tens of microbarn in the astrophysical energy region. Despite of this, $^{16}$O plays an important role as neutron poison in the astrophysical slow neutron capture ($s$) process due to its high abundance. We present in this paper a re-evaluation of the available experimental data for $^{16}$O($n,\gamma$)$^{17}$O and derive a new recommendation for the Maxwellian-averaged cross sections (MACS) between $kT$= 5$-$100 keV. Our new recommendations are lower up to $kT$= 60 keV compared to the previously recommended values but up to 14\% higher at $kT$= 100 keV. We explore the impact of this different energy dependence on the weak $s$-process during core helium- ($kT$= 26 keV) and shell carbon burning ($kT$= 90 keV) in massive stars where $^{16}$O is the most abundant isotope.