Thermal neutron capture cross section of the radioactive isotope Fe 60

Abstract

Background: Fifty percent 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. Purpose: One of the fundamental signatures for active nucleosynthesis in our galaxy is the observation of long-lived radioactive isotopes, such as Fe60 with a half-life of 2.60×106 yr. To reproduce this γ activity in the universe, the nucleosynthesis of Fe60 has to be understood reliably. Methods: An Fe60 sample produced at the Paul Scherrer Institut (Villigen, Switzerland) was activated with thermal and epithermal neutrons at the research reactor at the Johannes Gutenberg-Universität Mainz (Mainz, Germany). Results: The thermal neutron capture cross section has been measured for the first time to σth=0.226(-0.049+0.044)b. An upper limit of σRI<0.50b could be determined for the resonance integral. Conclusions: An extrapolation towards the astrophysically interesting energy regime between kT=10 and 100 keV illustrates that the s-wave part of the direct capture component can be neglected.