Determination of the sub-threshold contribution in the 13C(α,n)16O reaction for the neutrons of s-process

Abstract A large enhancement of the 13 C(α,n) 16 O reaction cross section at low energy limit due to the sub-threshold state in 17 O has been predicted, explaining the neutron source of s-process nucleosynthesis. By the 13 C( 6 Li,d) 17 O transfer reaction, we had deduced the resonance strength of the state. Contrary to the predictions, the sub-threshold state was found to have very small contribution to the astrophysical S factor.