Revolutionising Detection Systems For Intercepting The Illicit Transportation Of Radioactive Materials Concealed Within Shipping Containers

Resulting from an increase in the global volume of nuclear and radioactive materials under regulatory control as the international community moves towards greater nuclear power provision as part of a low-carbon energy mix, there are consequently expanding opportunities for the loss or theft of such materials that could be fabricated into improvised nuclear explosive or radiological dispersal devices. To prevent these dangerous materials falling into the hands of malicious actors, it is essential to deter and detect its illicit transportation when concealed within shipping containers. As these constitute a significant proportion of global trade, implementing a robust shipping container screening system at seaports represents a crucial national security consideration. As part of existing screening systems, shipping containers are driven through radiation portal monitors (RPMs) comprising plastic scintillators for gamma detection and separate, typically He-3 based, neutron detectors. These polyvinyl toluene plastic-based scintillators enable current screening systems to meet detection sensitivity standards owing to their economical manufacturing in large sizes, producing high geometric efficiency detectors, however, their poor spectral resolution fundamentally limits the screening process to making binary "source" or "no source" decisions, necessitating a secondary, and more thorough, inspection phase for suspect containers. The next generation of shipping container screening systems should be comparable in throughput and cost to existing systems, but have the energy resolution to identify specific radionuclides and the spatial resolution to localise their position within a container, therefore expediting the screening process and eliminating the requirement for time-consuming and costly secondary inspection. By simulation using Monte Carlo/deterministic methods and experimental validation, this work evaluates the material and configurational properties of detection systems, alongside the data collection and processing algorithms employed, to develop prospective shipping container screening systems capable of characterising concealed gamma-emitting sources. One research area of particular interest is the incorporation of inorganic scintillator detectors into lifting equipment employed at ports to load and unload containers from ships, representing an opportunity to take extended measurements of a shipping container at short stand-off distances using geometrically favorable detector configurations that, combined with advanced data processing algorithms, enable the enhanced isotopic and locational characterisation of concealed sources.