Gamma-Ray-Production Cross Sections for the 56 Fe( n,n’y ) Reaction from 2.5- to 14.1-MeV Neutron Energies

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Abstract
Differential production cross sections for gamma rays from the 56Fe(n,n’y) reactions are presented for incident-neutron energies between 2.5 and 14.1 MeV. The reactions are studied at 11 neutron energies using pulsed beam techniques with the D(d, n)3He reaction and associated particle method with the T(d,n)4He reaction as neutron sources and using a sample of natural iron. The excitation functions of 17 gamma-ray transitions were measured between 4.8- and 8.8-MeV incident energies in nine 0.5-MeV steps at an angle of 90 deg. Angular distributions of 13 prominent gamma rays were also measured at 8.8-MeV neutron energy and for the 846.8- and 1238.3-keV gamma rays at 2.5- and 14.1-MeV neutron energies. Comparisons with previously published measurements and with the calculated cross sections of the Hauser-Feshbach formalism are presented. The calculated cross sections include the effects of level-width fluctuations, and agree well with the data when all levels observed are included. This agreement renders unnecessary the added contribution from a supposed continuum-like spectrum of unresolved final states for measurements up to 8.8-MeV incident energy. Such a contribution, proposed in previous studies, has been shown to be small. On the basis of the comparison between present data and that of previous authors, such a contribution cannot exceed 15% of the summed cross sections for discrete lines up to 7.3-MeV incident-neutron energy.

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