Uncertainty of the astrophysical O17,18(α,n)Ne20,21 reaction rates and the applicability of the statistical model for nuclei with A≲20

Abstract

Background: The $(\ensuremath{\alpha},n)$, and $(\ensuremath{\alpha},\ensuremath{\gamma})$ reactions on $^{17,18}\mathrm{O}$ have significant impact on the neutron balance in the astrophysical $s$ process. In this scenario stellar reaction rates are required for relatively low temperatures below ${T}_{9}\ensuremath{\lesssim}1$.Purpose: The uncertainties of the $^{17,18}\mathrm{O}(\ensuremath{\alpha},n)^{20,21}\mathrm{Ne}$ reactions are investigated. Statistical model calculations are performed to study the applicability of this model for relatively light nuclei in extension to a recent review for the $20\ensuremath{\le}A\ensuremath{\le}50$ mass range.Method: The available experimental data for the $^{17,18}\mathrm{O}(\ensuremath{\alpha},n)^{20,21}\mathrm{Ne}$ reactions are compared with statistical model calculations. Additionally, the reverse $^{20}\mathrm{Ne}(n,\ensuremath{\alpha})^{17}\mathrm{O}$ reaction is investigated, and similar studies for the $^{17}\mathrm{F}$ mirror nucleus are provided.Results: It is found that, on average, the available experimental data for $^{17}\mathrm{O}$ and $^{18}\mathrm{O}$ are well described within the statistical model, resulting in reliable reaction rates above ${T}_{9}\ensuremath{\gtrsim}1.5$ from these calculations. However, significant experimental uncertainties are identified for the $^{17}\mathrm{O}(\ensuremath{\alpha},{n}_{0})^{20}\mathrm{Ne}$ (ground state) channel.Conclusions: The statistical model is able to predict astrophysical reaction rates for temperatures above 1 GK with uncertainties of less than a factor of two for the nuclei under study. An experimental discrepancy for the $^{17}\mathrm{O}(\ensuremath{\alpha},n)^{20}\mathrm{Ne}$ reaction needs to be resolved.