A New Formula for Computing Mean Neutron Exposure

摘要

We have investigated the characteristics of the distribution of neutron exposures (“DNE” hereafter) in the He-shell nucleosynthesis regions in the model of s-process nucleosynthesis in low-mass AGB (Asymptotic Giant Branch) stars in 13C radiatively burning conditions. The result indicates that although the DNE obtained with this model is still approximately exponential, like those of the previous convective s-process scenarios, the relation between the neutron exposure Δτ of each pulse and the mean neutron exposure τ0 is no longer τ0 = _Δτ/ln r, rather, it is now approximately τ0 = _Δτ/ ln{q[1.0020 + 0.6602(r _ q) + 4.6125(r _ q)2_ 10.8962(r _ q)3+ 13.9138(r _ q)4]} (r is the overlap factor, q is the mass ratio of the 13C shell to the He shell). This formula unifies the stellar model of radiative s-process with the classical model from the angle of DNE.