Optimization of a photoneutron source based on 10 MeV electron beam using Geant4 Monte Carlo code

Abstract

Geant4 Monte Carlo code has been used to conceive and optimize a simple and compact neutron source based on a 10MeV electron beam impinging on a tungsten target adjoined to a beryllium target. For this purpose, a precise photonuclear reaction cross-section model issued from the International Atomic Energy Agency (IAEA) database was linked to Geant4 to accurately simulate the interaction of low energy bremsstrahlung photons with beryllium material. A benchmark test showed that a good agreement was achieved when comparing the emitted neutron flux spectra predicted by Geant4 and Fluka codes for a beryllium cylinder bombarded with a 5MeV photon beam. The source optimization was achieved through a two stage Monte Carlo simulation. In the first stage, the distributions of the seven phase space coordinates of the bremsstrahlung photons at the boundaries of the tungsten target were determined. In the second stage events corresponding to photons emitted according to these distributions were tracked. A neutron yield of 4.8×1010neutrons/mA/s was obtained at 20cm from the beryllium target. A thermal neutron yield of 1.5×109neutrons/mA/s was obtained after introducing a spherical shell of polyethylene as a neutron moderator.