Simulation study of a photoneutron source for Bragg edge transmission imaging

Abstract A neutron source with large enough cold neutron flux ( ∼ 10 3 n/cm 2 /s), continuous energy spectrum and good wavelength resolution ( ∼ 0.5%) is required to realize Bragg edge transmission imaging (BETI) for the residual stress measurement of metals or other materials. A photoneutron source based on a 10-MeV/20-kW e-LINAC is proposed to meet these requirements for its compact size and working robustness. Heavy water is used to convert the bremsstrahlung photons to intense photoneutrons, with polyethylene(PE) and 30 K solid CH 4 acting as the pre-moderator and the main moderator to acquire cold neutrons, respectively. The structure of the photoneutron source is optimized by simulation to balance the neutron intensity and wavelength resolution. The simulation results show that the cold neutron flux could achieve 3.4 × 10 4 n/cm 2 /s at a position of 6 m from the source with a wavelength resolution better than 3%, or 1.4 × 10 3 n/cm 2 /s flux at a position of 30 m from the source with a wavelength resolution better than 0.5%.