Cross-Section Measurements of the 86Kr(γ, n) Reaction to Probe the s-Process Branching at 85Kr

We have carried out photodisintegration cross-section measurements on Kr-86 using monoenergetic photon beams ranging from the neutron separation energy, S-n = 9.86 MeV, to 13 MeV. We combine our experimental Kr-86(gamma, n)Kr-85 cross section with results from our recent Kr-86(gamma, gamma') measurement below the neutron separation energy to obtain the complete nuclear dipole response of Kr-86. The new experimental information is used to predict the neutron capture cross section of Kr-85, an important branching point nucleus on the abundance flow path during s-process nucleosynthesis. Our new and more precise Kr-85(n, gamma)Kr-86 cross section allows us to produce more precise predictions of the Kr-86 abundance from s-process models. In particular, we find that the models of the s process in asymptotic giant branch stars of mass <1.5M(circle dot), where the C-13 neutron source burns convectively rather than radiatively, represent a possible solution for the highest Kr-86:Kr-82 ratios observed in meteoritic stardust SiC grains.