Neutrons for active detection of special nuclear material: An intense pulsed 7Li(p,n)7Be source

An ongoing program me looking at the active detection of special nuclear material (SNM) is being undertaken by the Atomic Weapons Establishment (A WE) in collaboration with the Naval Research Laboratory (NRL). As part of this programme, pulsed-power driven neutron experiments were conducted at the NRL Mercury accelerator. Mercury was used in a positive polarity mode to produce and accelerate protons into lithium metal foils, generating neutrons via the ⁷Li(p,n)⁷Be reaction. 13 shots were carried out at varying machine voltages and over 30 separate neutron and gamma-ray diagnostics were fielded to characterise the angular distribution and energy spectrum of the neutrons generated. Machine performance, neutron, and gamma-ray data are presented and discussed. Neutron yields of up to 1011 neutrons/steradian were recorded, with yields at 60° off axis being approximately 50% of the on axis yield. Previously published analysis [1] of data has been used to validate GEANT4 modelling of the experiments (2). Machine performance data has been used in conjunction with modelled neutron spectra to predict the performance of the Mercury ⁷Li(p,n)⁷Be source as a system for detecting SNM.