Study on the keV neutron capture reaction in ⁵⁶Fe and ⁵⁷Fe

The neutron capture cross-sections and the radiative capture gamma-ray spectra from the broad resonances of ⁵⁶Fe and ⁵⁷Fe in the neutron energy range from 10 to 90 keV and 550 keV have been measured with an anti-Compton NaI(Tl) detector. Pulsed keV neutrons were produced from the ⁷Li(p, n)⁷ Be reaction by bombarding the lithium target with the 1.5 ns bunched proton beam from the 3 MV Pelletron accelerator. The incident neutron spectrum on a capture sample was measured by means of a time-of-flight (TOF) method with a ⁶Li-glass detector. The number of weighted capture counts of the iron or gold sample was obtained by applying a pulse height weighting technique to the corresponding capture gamma-ray pulse height spectrum. The neutron capture gamma-ray spectra were obtained by unfolding the observed capture gamma-ray pulse height spectra. To achieve further understanding on the mechanism of neutron radiative capture reaction and study on physics models, theoretical calculations of the γ-ray spectra for ⁵⁶Fe and ⁵⁷Fe with the POD program have been performed by applying the Hauser-Feshbach statistical model. The dominant ingredients to perform the statistical calculation were the Optical Model Potential (OMP), the level densities described by the Mengoni-Nakajima approach, and the γ-ray transmission coefficients described by γ-ray strength functions. The comparison of the theoretical calculations, performed only for the 550 keV point, show a good agreement with the present experimental results.