The 95zr(n, gamma)96zr cross section from the surrogate ratio method and its effect on the s-process nucleosynthesis

TL;DR

This study measures the 95Zr(n,gamma)96Zr reaction cross section using surrogate methods, revealing significant differences from previous estimates and demonstrating its impact on s-process nucleosynthesis models in stars.

Contribution

It introduces a surrogate ratio method to determine the 95Zr(n,gamma)96Zr cross section and assesses its effects on stellar nucleosynthesis modeling.

Findings

Maxwellian-averaged cross section of 66±16 mb at 30 keV

New rate increases 96Zr production by up to 80% in certain stellar models

Rate aligns with some meteoritic data for stars below 4 solar masses

Abstract

The 95Zr(n,gamma)96Zr reaction cross section is crucial in the modelling of s-process nucleosynthesis in asymptotic giant branch stars because it controls the operation of the branching point at the unstable 95Zr and the subsequent production of 96Zr. We have carried out the measurement of the 94Zr(18O,16O) and 90Zr(18O,16O) reactions and obtained the gamma-decay probability ratio of 96Zr* and 92Zr* to determine the 95Zr(n,gamma)96Zr 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. (2000), but 30% and more than a factor of two larger than the values proposed by Toukan & Kappeler (1990) and Lugaro et al. (2014), respectively, and routinely used in s-process models. We tested the new rate in stellar models with masses between 2 and 6 Msun and metallicities 0.014 and 0.03. The largest changes - up 80% variations in 96Zr - are seen in models of mass 3-4 Msun, where the 22Ne neutron source is mildly activated. The new rate can still provide a match to data from meteoritic stardust silicon carbide grains, provided the maximum mass of the parent stars is below 4 Msun, for a metallicity of 0.03.