At the high temperature and density conditions of hot or explosive helium burning, the ${}^{18}\mathrm{F}(\alpha ,p){}^{21}\mathrm{Ne}$ reaction may compete successfully with the ${}^{18}\mathrm{F}({\beta }^{+}\nu )$ decay. This suggests ${}^{21}\mathrm{Ne}(\alpha ,n)$ as an alternative neutron source in the $r$-process. We have determined the total cross section of the ${}^{18}\mathrm{F}(\alpha ,p){}^{21}\mathrm{Ne}$ reaction by studying the time-reverse reaction ${}^{21}\mathrm{Ne}(p,\alpha ){}^{18}\mathrm{F}$. Using the activation technique, the total reaction yield was measured in the proton beam energy range of 2.3–4.0 MeV, which corresponds to energies of 0.5–2.1 MeV in the ${}^{18}\mathrm{F}+\alpha$ system. The resulting yield curve was analyzed in terms of the thick target formalism and the $R$-matrix theory. The reaction rate was deduced experimentally for the first time for the temperature of $0.1<T_9<1$. The experimental reaction rate was compared with Hauser-Feshbach predictions. The astrophysical implications of the new rate are discussed.

• Received 9 June 2009

DOI:https://doi.org/10.1103/PhysRevC.80.025805