Monte Carlo simulation of neutron radiography 2 (NUR-2) system at triga mark II research reactor of Malaysian Nuclear Agency

Abstract

The imaging properties namely the edge spread function (ESF) and line spread function (LSF) of the Neutron Radiography 2 (NUR-2) system at Triga Mark II Reactor at Malaysian Nuclear Agency were investigated via simulation and experiment. The simulation of radiographic image was performed by using the Monte Carlo N-Particle codes version 5 and the real neutron radiographic images were collected from experiment done at NUR-2 facility. The simulation used Flux Image Radiograph (FIR) tally while for the experiment the direct method using film was used to detect the transported neutrons. The ESF of the system was measured using cadmium foil with thickness of 1 mm, 2 mm and 3 mm which blocked half of the neutron beam. Demineralized water was used as a scattering material to study the neutron scattering effect inside the material where it was placed between the cadmium foil and the detector. The differentiation of the ESF gave the LSF of the system and the full width at half maximum (FWHM) was estimated. From fast Fourier transformation of the LSF, the modulation transfer function (MTF) of the system was obtained. The results showed that the simulated neutron patterns without scattering material were similar to those found in experiment but with the presence of scattering material, the simulation and experimental data showed great differences. Cadmium with thickness of 1 mm gave the best spatial frequency response followed by 2 mm and 3 mm thick of cadmium. The range of spatial frequency for MTF at 20% was 1.0 to 2.5 cycle/mm, while the range of FWHM was 0.3 to 0.5 mm. The FWHM and MTF obtained in this study are valuable for the characterization of imaging properties of the neutron radiography system.