Dosimetry foil characterisation of a new lithium-target fast neutron source

Abstract

Accelerator-based lithium-target neutron sources produce fast neutron spectra ideal for nuclear data studies, but simulations of these neutron spectra are not always reliable. Methods for characterising neutron spectra with dosimetry foils have been developed for a new compact fast neutron source at the Birmingham MC40 Cyclotron Facility. Measurements of a Li ( p , x n ) neutron spectrum from 16 MeV protons are used to evaluate the MCNP model of the neutron source, and validate a probabilistic neutron spectrum adjustment method. Measurement of 7 Be activation in the target was used to estimate total flux, and inventory simulations were used to evaluate the modelled spectrum and adjusted spectrum. Spectrum adjustment was performed with Monte-Carlo uncertainty estimation, using probability distributions for the reaction rate measurements, response functions and the a priori spectrum. Comparison of the MCNP model predictions to measurements showed the JENDL-5 proton library inaccurately models some neutron production mechanisms. Evaluation of the adjusted neutron spectrum predictions showed they were consistent with the measurements for fast neutrons.