The ⁵⁹Fe (n,γ) ⁶⁰Fe Cross Section from the Surrogate Ratio Method and Its Effect on the ⁶⁰Fe Nucleosynthesis

Abstract

Abstract The long-lived 60 Fe (with a half-life of 2.62 Myr) is a crucial diagnostic of active nucleosynthesis in the Milky Way galaxy and in supernovae near the solar system. The neutron-capture reaction 59 Fe(n, γ ) 60 Fe on 59 Fe (half-life = 44.5 days) is the key reaction for the production of 60 Fe in massive stars. This reaction cross section has been previously constrained by the Coulomb dissociation experiment, which offered partial constraint on the E 1 γ -ray strength function but a negligible constraint on the M 1 and E 2 components. In this work, for the first time, we use the surrogate ratio method to experimentally determine the 59 Fe(n, γ ) 60 Fe cross sections in which all the components are included. We derived a Maxwellian-averaged cross section of 27.5 ± 3.5 mb at kT = 30 keV and 13.4 ± 1.7 mb at kT = 90 keV, roughly 10%–20% higher than previous estimates. We analyzed the impact of our new reaction rates in nucleosynthesis models of massive stars and found that uncertainties in the production of 60 Fe from the 59 Fe(n, γ ) 60 Fe rate are at most 25%. We conclude that stellar physics uncertainties now play a major role in the accurate evaluation of the stellar production of 60 Fe.