A Monte Carlo model of the Dingo thermal neutron imaging beamline

Abstract

In this study, we present a validated Geant4 Monte Carlo simulation model of the Dingo thermal neutron imaging beamline at the Australian Centre for Neutron Scattering. The model, constructed using CAD drawings of the entire beam transport path and shielding structures, is designed to precisely predict the in-beam neutron field at the position at the sample irradiation stage. The model’s performance was assessed by comparing simulation results to various experimental measurements, including planar spatial thermal neutron distribution obtained in-beam using gold foil activation and 10B4C-coated microdosimeters and the out-of-beam neutron spectra measured with Bonner spheres. The simulation results demonstrated that the predicted neutron fluence at the field’s centre is within 8.1% and 2.1% of the gold foil and 10B4C-coated microdosimeter measurements, respectively. The logarithms of the ratios of average simulated to experimental fluences in the thermal (Eth < 0.414 eV), epithermal (0.414 eV < Eepi < 11.7 keV) and fast (Efast > 11.7 keV) spectral regions were approximately -0.03 to +0.1, -0.2 to +0.15, and -0.4 to +0.2, respectively. Furthermore, the predicted thermal, epithermal and fast neutron components in-beam at the sample stage position constituted approximately 18%, 64% and 18% of the total neutron fluence.