The Fe-59 (N,Gamma) Fe-60 Cross Section From The Surrogate Ratio Method And Its Effect On The Fe-60 Nucleosynthesis

The long-lived Fe-60 (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 Fe-59(n,gamma)Fe-60 on Fe-59 (half-life = 44.5 days) is the key reaction for the production of Fe-60 in massive stars. This reaction cross section has been previously constrained by the Coulomb dissociation experiment, which offered partial constraint on the E1 gamma-ray strength function but a negligible constraint on the M1 and E2 components. In this work, for the first time, we use the surrogate ratio method to experimentally determine the Fe-59(n,gamma)Fe-60 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 Fe-60 from the Fe-59(n,gamma)Fe-60 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 Fe-60.