Modelling of the 7Li(p,n)7Be neutron yield from mercury using GEANT-4 and LSP

An ongoing programme looking at the active detection of special nuclear material is being undertaken by the Atomic Weapons Establishment in collaboration with the Naval Research Laboratory (NRL). As part of this programme, proton beam generation experiments were conducted at the NRL Mercury pulsed power accelerator using a lithium metal cathode to generate neutrons through the ⁷Li(p,n)⁷Be reaction. A modification to GEANT4 to include the ⁷Li(p,n)⁷Be reaction for the purposes of modeling the doubly differential neutron yield from these experiments has been implemented. The Large Scale Plasma (LSP) Particle-in-Cell (PiC) code was used to obtain the proton kinematics and flux at the lithium conversion target; an algorithm was subsequently written to transform this data to a complete GEANT4 source description. The modification to the GEANT4 simulation toolkit is presented and the output compared to experimental data with good agreement. The work presented shows that the new GEANT4 process alongside the existing packages can be used to model the ⁷Li(p,n)⁷Be reaction with reasonable accuracy given an input proton phase space from a suitable simulation code such as LSP.