Optimization design of the collimator for fast neutron radiography system based on 600 kV Cockcroft-Walton accelerator

Fast neutron radiography (FNR) is a powerful non-destructive testing technique, particularly suitable for inspecting large and high-density objects. As a core component of FNR systems, the collimator critically determines the quality of the radiographic image, primarily affecting its resolution and contrast. In this study, we present a systematic design optimization of the collimator for an FNR system based on a 600 kV Cockcroft-Walton accelerator at China Institute of Atomic Energy (CIAE). Monte Carlo simulations were employed to enhance key performance metrics, including beam purity and spatial resolution. The simulation results demonstrate a substantial improvement in neutron beam quality achieved by the optimized design. Specifically, within the imaging field of view, the proportion of effective imaging neutrons increased by approximately 8%, and the neutron-to-gamma fluence ratio was enhanced by a factor of ∼80. Consequently, the spatial resolution of the system was improved from 3.88 mm to 0.92 mm. These findings not only establish a solid foundation for the forthcoming experimental phase of this project but also offer valuable guidance for collimator design in similar accelerator-based FNR systems.