The 95Zr(n, γ)96Zr Cross Section from the Surrogate Ratio Method and Its Effect on s-process Nucleosynthesis

The Zr-95(n, gamma)Zr-96 reaction cross section is crucial in the modeling of s-process nucleosynthesis in asymptotic giant branch stars because it controls the operation of the branching point at the unstable Zr-95 and the subsequent production of Zr-96. We have carried out the measurement of the Zr-94(O-18, O-16) and Zr-90(O-18, O-16) reactions and obtained the gamma-decay probability ratio of Zr-96* and Zr-92* to determine the Zr-95(n, gamma)Zr-96 reaction cross sections with the surrogate ratio method. Our deduced Maxwellian-averaged cross section of 66 +/- 16 mb at 30 keV is close to the value recommended by Bao et al., but 30% and more than a factor of two larger than the values proposed by Toukan & Kappeler and Lugaro et al., respectively, and routinely used in s-process models. We tested the new rate in stellar models with masses between 2 and 6 M-circle dot and metallicities of 0.014 and 0.03. The largest changes-up to 80% variations in Zr-96-are seen in models of mass 3-4 M-circle dot, where the Ne-22 neutron source is mildly activated. The new rate can still provide a match to data from meteoritic stardust silicon carbide grains, provided that the maximum mass of the parent stars is below 4 M-circle dot, for a metallicity of 0.03.