Study of Neutron Source Reaction ¹³C(α，n)¹⁶O in Stars

¹³C(α,n)¹⁶O is the main neutron source reaction of slow neutron capture (s) process in asymptotic giant branch (AGB) stars. The 6.356 MeV 1/2⁺ subthreshold resonance in ¹⁷O plays an important role in the ¹³C(α,n)¹⁶O reaction. The ¹³C(¹¹B, ⁷Li)¹⁷O angular distributions were measured using HI-13 tandem accelerator and Q3D magnetic spectrograph, and then used to determine the α-width of the subthreshold resonant state which is currently the most uncertain parameter for determining the ¹³C(α,n)¹⁶O reaction rate. By using the present α-width, the astrophysical S-factor and the stellar rate of the ¹³C(α,n)¹⁶O reaction were derived. This shed some light on the existing discrepancies up to a factor of 25 in S-factors derived from different authors. The simulation of s-process in AGB stars shows that the new reaction rate produces 25% more Pb than the CF88 compilation.