The thermal neutron capture cross section of the radioactive isotope $^{60}$Fe

TL;DR

This study measures the thermal neutron capture cross section of radioactive $^{60}$Fe, providing essential data for astrophysical nucleosynthesis models and improving understanding of the isotope's cosmic abundance.

Contribution

First measurement of the thermal neutron capture cross section of $^{60}$Fe, crucial for modeling stellar nucleosynthesis and cosmic isotope production.

Findings

Thermal neutron capture cross section of $^{60}$Fe is 0.226 b.

Resonance integral upper limit is 0.50 b.

Direct capture component is negligible at astrophysical energies.

Abstract

50% of the heavy element abundances are produced via slow neutron capture reactions in different stellar scenarios. The underlying nucleosynthesis models need the input of neutron capture cross sections. One of the fundamental signatures for active nucleosynthesis in our galaxy is the observation of long-lived radioactive isotopes, such as $^{60}$Fe with a half-life of $2.60\times10^6$ yr. To reproduce this $\gamma$-activity in the universe, the nucleosynthesis of $^{60}$Fe has to be understood reliably. A $^{60}$Fe sample produced at the Paul-Scherrer-Institut was activated with thermal and epithermal neutrons at the research reactor at the Johannes Gutenberg-Universit\"at Mainz. The thermal neutron capture cross section has been measured for the first time to $\sigma_{\text{th}}=0.226 \ (^{+0.044}_{-0.049})$ b. An upper limit of $\sigma_{\text{RI}} < 0.50$ b could be determined for the resonance integral. An extrapolation towards the astrophysicaly interesting energy regime between $kT$=10 keV and 100 keV illustrates that the s-wave part of the direct capture component can be neglected.