Optimising the neutron environment of Radiation Portal Monitors: a computational optimisation study

TL;DR

This study uses computational simulations to optimize the design of Radiation Portal Monitors, significantly enhancing their sensitivity to neutron signatures by adjusting shielding, collimation, and air gaps.

Contribution

It introduces a computational optimization approach to improve RPM sensitivity through design modifications that are simple and cost-effective.

Findings

Detector response improved by over 2 times with optimized shielding and collimation.

Air gap optimization further enhances detector efficiency.

Design modifications are applicable to existing RPMs for better threat detection.

Abstract

Efficient and reliable detection of radiological or nuclear threats is a crucial part of national and international efforts to prevent terrorist activities. Radiation Portal Monitors (RPMs), which are deployed worldwide, are intended to interdict smuggled fissile material by detecting emissions of neutrons and gamma rays. However, considering the range and variety of threat sources, vehicular and shielding scenarios, and that only a small signature is present, it is important that the design of the RPMs allows these signatures to be accurately differentiated from the environmental background. Using Monte-Carlo neutron-transport simulations of a model helium-3 detector system we have conducted a parameter study to identify the optimum combination of detector shielding and collimation that maximises the sensitivity of RPMs. These structures, which could be simply and cost-effectively added to existing RPMs, can improve the detector response by more than a factor of two relative to an unmodified, bare design. Furthermore, optimisation of the air gap surrounding the helium tubes also improves detector efficiency.