Broad levels in ${}^{17}\text{O}$ and their relevance for the astrophysical $s$ process

Levels in ${}^{17}\text{O}$ affect the astrophysical $s$ process in two opposite ways. The neutron production is enhanced by resonances in the ${}^{13}\text{C}(\alpha ,n){}^{16}\text{O}$ reaction at excitation energies around 7 MeV in ${}^{17}\text{O}$, and the number of available neutrons is reduced by low-lying resonances in the ${}^{16}\text{O}(n,\gamma ){}^{17}\text{O}$ reaction corresponding to levels in ${}^{17}\text{O}$ with excitation energies of $4–5\text{MeV}$. The present work uses the ${}^{19}\text{F}(d,\alpha ){}^{17}\text{O}$ reaction to determine absolute widths of the relevant levels in ${}^{17}\text{O}$. The results improve the uncertainties of the previously adopted values and resolve a discrepancy between recent studies for the $1/2^{+}$ level close to the threshold of the ${}^{13}\text{C}(\alpha ,n){}^{16}\text{O}$ reaction. In addition, improved excitation energies and widths are provided for several states in ${}^{17}\text{O}$ up to excitation energies close to 8 MeV.

Figure 1

Low energy spectrum for the ${}^{19}\text{F}(d,\alpha ){}^{17}\text{O}$ reaction at ${\mathrm{\Theta }}_{\mathrm{lab}}={15}^{\circ }$.

Figure 2

High energy spectrum for the ${}^{19}\text{F}(d,\alpha ){}^{17}\text{O}$ reaction at ${\mathrm{\Theta }}_{\mathrm{lab}}={10}^{\circ }$. The data ranges that have been used to fit the two Lorentzians are indicated by the green (lighter) dots. The simultaneously fitted background (dotted) and the total fit function (dashed) are also shown. The strongest peak at 7075 keV is the only background line from the ${}^{16}\text{O}(d,{\alpha }_0){}^{14}\text{N}$ reaction.