One-dimensional localization of fast neutrons and gamma rays using a GAGG-based directional probe: A Monte Carlo study

Localization of fast-neutron and gamma-ray sources in mixed fields is important for nuclear safety and security, but it remains unclear whether a GAGG-based probe can be adapted for dual-particle sensing. In this work, an outer hollow high-density polyethylene cylinder was added to a previously reported GAGG-based gamma-ray directional probe to moderate incident fast neutrons. Monte Carlo simulations were performed for a single 252 Cf point source and a single 137 Cs point source under far-field conditions. An 80 keV secondary prompt-gamma signal for fast-neutron localization and a 662 keV gamma-ray signal were discriminated by energy windowing, and a centroid-vector-based algorithm was used for one-dimensional localization. An HDPE radial thickness of 60 mm was selected as a trade-off between fast-neutron and gamma-ray efficiencies. The proposed system achieved separate localization of one fast-neutron source and one gamma-ray source in a mixed field. Localization bias decreased with increasing valid events for both particle types, although neutron localization remained less accurate and showed a narrower reliable field of view than gamma-ray localization. These results demonstrate the feasibility of one-dimensional far-field dual-particle localization using the proposed GAGG-based directional probe.