Astrophysical Reaction Rate for the Neutron-Generator Reaction ¹³C(α,n)¹⁶O in Asymptotic Giant Branch Stars

The reaction ¹³C(α,n) is considered to be the main source of neutrons for the s process in asymptotic giant branch stars. At low energies, the cross section is dominated by the 1/2⁺ 6.356 MeV subthreshold resonance in ¹⁷O whose contribution at stellar temperatures is uncertain by a factor of 10. In this work, we performed the most precise determination of the low-energy astrophysical S factor using the indirect asymptotic normalization (ANC) technique. The α-particle ANC for the subthreshold state has been measured using the sub-Coulomb α-transfer reaction (⁶Li,d). Using the determined ANC, we calculated S(0), which turns out to be an order of magnitude smaller than in the nuclear astrophysics compilation of reaction rates.