Current and Prospective Radiation Detection Systems, Screening Infrastructure and Interpretive Algorithms for the Non-Intrusive Screening of Shipping Container Cargo: A Review

Abstract

The non-intrusive screening of shipping containers at national borders serves as a prominent and vital component in deterring and detecting the illicit transportation of radioactive and/or nuclear materials which could be used for malicious and highly damaging purposes. Screening systems for this purpose must be designed to efficiently detect and identify material that could be used to fabricate radiological dispersal or improvised nuclear explosive devices, while having minimal impact on the flow of cargo and also being affordable for widespread implementation. As part of current screening systems, shipping containers, offloaded from increasingly large cargo ships, are driven through radiation portal monitors comprising plastic scintillators for gamma detection and separate, typically 3He-based, neutron detectors. Such polyvinyl-toluene plastic-based scintillators enable screening systems to meet detection sensitivity standards owing to their economical manufacturing in large sizes, producing high-geometric-efficiency detectors. However, their poor energy resolution fundamentally limits the screening system to making binary “source” or “no source” decisions. To surpass the current capabilities, future generations of shipping container screening systems should be capable of rapid radionuclide identification, activity estimation and source localisation, without inhibiting container transportation. This review considers the physical properties of screening systems (including detector materials, sizes and positions) as well as the data collection and processing algorithms they employ to identify illicit radioactive or nuclear materials. The future aim is to surpass the current capabilities by developing advanced screening systems capable of characterising radioactive or nuclear materials that may be concealed within shipping containers.

Radioactive Source Localization Using a Mobile Radiation Detection System Featuring Informed Path-Based Decisions

“…Benefits of employing a detector network for the identification and tracking of moving radioactive sources, as opposed to relying on a single detector, include an enhanced detection coverage and increased results confidence [4]. In [5] a combination of fixed and mobile detectors is suggested to achieve comprehensive coverage of seaport areas. The potential of mobile radiation detection systems (MRDS) to be deployed in any location, as opposed to fixed RPMs, enhances their effectiveness in deterring malevolent and terrorist acts [6].…”

“…A review of algorithms used for detecting and localizing radioactive sources is presented in [5] [8] . For instance, [25] employs a maximum likelihood estimation algorithm and a fixed detector network with five 51 mm × 51 mm NaI(Tl) scintillators to localize a 189 kBq 137 Cs source within a 5 m × 5 m × 5 m space domain with an accuracy better than 60 cm (2-3 minutes).…”

A mobile radiation detection system for security inspection and monitoring

“…Although predefined paths can be used to create a radiation map of the area of interest (e.g., parallel sweeping search pattern) [9] [10], advantages can be found in utilizing real-time (or near real-time) radiation data gathered by the detectors and sensors to optimize the detection system path (informed path) and survey time [1]. Several radioactive hotspot localization algorithms have been described in literature [2] [12], such as the use of a maximum likelihood estimation (MLE) algorithm [13] [14], the use of a radiation detector network [15] [16] and the application of deep learning approaches [17].…”

Neutron and Gamma-Ray Detection System Coupled to a Multirotor for Screening of Shipping Container Cargo

“…According to Martin and Connolly [ 8 ] a well-designed screening system should efficiently detect and identify radioactive materials and SNMs that could be used to fabricate a RDD or an IND, while keeping the normal flow of cargo affordable so that it can be easily replicated. At the seaports, this is normally achieved via a two-stage process: (i) a primary inspection in which the shipping containers pass through a large polyvinyl-toluene (PVT) plastic scintillators (high geometric detection efficiency) for gamma-ray detection and, in some cases, neutron detectors based normally in 3 He tube detectors.…”