Neutron transport benchmark on iron using a white high-energy neutron field

A benchmark experiment has been conducted on iron at the U-120 M cyclotron of the Nuclear Physics Institute, Rez. The D2O(3He, xn) reaction was employed with 40 MeV helium ions to produce an International Fusion Material Irradiation Facility (IFMIF) like white neutron source spectrum. Spectra of neutrons from both the bare source and transmitted through a 20 cm thick iron slab were measured with an NE-213 scintillation detector in the energy range 3.5–35 MeV by the pulse height technique. The computational analysis of the experiment was performed with the MCNPX and MCNP4C Monte Carlo codes and iron cross-section data from the Institute of Nuclear Power Engineering/Forschungszentrum Karlsruhe and Los Alamos National Laboratory evaluations. It was found that MCNPX with a built-in nuclear reaction model fails to predict the 3He–D2O neutron source parameters. For the benchmarking of evaluated cross section data a detailed 3-d geometry model was devised to accurately represent the experimental set-up; the neutron source distribution being modelled on the basis of measured angle-energy neutron yields. The comparison of calculated and experimental neutron transmission spectra has shown satisfactory agreement.