Re-evaluation of the ${}^{16}$O($n$,${\hat{I}}^3$)${}^{17}$O cross section at astrophysical energies and its role as neutron poison in the $s$ process

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($n,{\hat{I}}^3$)${}^{17}$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.

13 pages, 7 figures; accepted for publication in Astrophys. J. (2016)