Measurement of Fast Neutron Spectra from Extended Samples

Abstract

The scattering of fast neutrons after passing through LiF and iron materials that are of possible use in the future fusion reactors has been studied at an incident neutron energy of 14.1 MeV using a neutron spectrometer employing the associated particles time-of-flight technique. The neutrons were produced by the T(d,n) 4He reaction using a 150 KV SAMES accelerator. The time of origin of the neutron was determined by detecting the associated alpha particles, and the neutron energy was determined by measuring its flight time over a fixed flight path. The angular energy distribution of fast neutrons after passing through samples of LiF and Fe were measured at several scattering angles. Fast neutron detection and associated alpha particle detection was by means of scintillation counters employing plastic scintillator type NE-102A. The samples used were of extended slab geometry of thickness approximately two mean free paths for Fe and of approximately one mean free path for LiF. Theoretical calculations based on primary and secondary scatter models have been carried out in the present work for computing the emerging flux from different thicknesses of LiF and Fe samples. The cross-section data and the angular energy distribution probabilities data for 6Li, 7Li, 19F and Fe were obtained from U.K.N.D.L. file. Experimental results show a reasonably good agreement with the theoretical results predicted by taking into account first and second scatters only, the predominant reaction being elastic scattering.