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Background: The ($alpha$,n) and ($alpha$,$gamma$) reactions on $^{17,18}$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 $T_9 lesssim 1$. Purpose: The uncertainties of the $^{17,18}$O($alpha$,n)$^{20,21}$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 $20 le A le 50$ mass range. Method: The available experimental data for the $^{17,18}$O($alpha$,n)$^{20,21}$Ne reactions are compared to statistical model calculations. Additionally, the reverse $^{20}$Ne(n,$alpha$)$^{17}$O reaction is investigated, and similar studies for the $^{17}$F mirror nucleus are provided. Results: It is found that on average the available experimental data for $^{17}$O and $^{18}$O are well described within the statistical model, resulting in reliable reaction rates above $T_9 gtrsim 1.5$ from these calculations. However, significant experimental uncertainties are identified for the $^{17}$O($alpha$,n$_0$)$^{20}$Ne(g.s.) 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 $^{17}$O($alpha$,n)$^{20}$Ne reaction needs to be resolved.
The ratio between the rates of the reactions O-17(alpha,n)Ne-20 and O-17(alpha,gamma)Ne-21 determines whether O-16 is an efficient neutron poison for the s process in massive stars, or if most of the neutrons captured by O-16(n,gamma) are recycled in
The competing $^{22}$Ne($alpha,gamma$)$^{26}$Mg and $^{22}$Ne($alpha,n$)$^{25}$Mg reactions control the production of neutrons for the weak $s$-process in massive and AGB stars. In both systems, the ratio between the corresponding reaction rates stro
Direct evidence of the $alpha$-cluster manifestation in bound states has not been obtained yet, although a number of experimental studies were carried out to extract the information of the clustering. In particular in conventional analyses of $alpha$
Uncertainties in the thermonuclear rates of the $^{15}$O($alpha,gamma$)$^{19}$Ne and $^{18}$F($p,alpha$)$^{15}$O reactions affect model predictions of light curves from type I X-ray bursts and the amount of the observable radioisotope $^{18}$F produc
Nuclear Astrophysics requires the knowledge of reaction rates over a wide range of nuclei and temperatures. In recent calculations the nuclear level density - as an important ingredient to the statistical model (Hauser-Feshbach) - has shown the highe