Measurement of Neutron Energy Spectrum below 10 keV in an Iron Shield Bombarded by Deuterium-Tritium Neutrons and Benchmark Test of Evaluated Nuclear Data from 14 MeV to 1 eV

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Neutron spectra below 10 keV in an iron shield assembly bombarded by deuterium-tritium neutrons are measured with accuracy between 5 to 13% by adopting the slowing-down time method. The measurement supplemented previous spectrum measurements for higher energies so that the neutron spectrum in the whole energy range from 14 MeV down to 0.3 eV is now available. Benchmark tests of iron data in JENDL-3.1, JENDL-3.2, JENDL fusion file, and FENDL/E-1.0 were carried out in the whole energy range with experimental uncertainty at ∼10% by utilizing the present and previous experiments. As a result, it was found that cross-section data in the newer versions of JENDL were improved in terms of agreement with the experiment. Calculation with JENDL fusion file and FENDL/E-1.0 could predict neutron fluxes in the whole energy range within 20 and 15%, respectively. Possible over- and underestimations for nonelastic and elastic cross sections, respectively, at 14 MeV in all JENDLs were pointed out. It was confirmed that low-energy neutron fluxes were very sensitive to Q values for discrete inelastic cross sections of natural iron and 57Fe(n,n’1,) reaction, which were not adequately treated in JENDL-3.1.