Speaker
Description
The reinforcement of detection and control measures for Special Nuclear Materials (SNM) and other radioactive substances used in sectors such as medicine, industry, environment, energy, agriculture, space, and research are critical for global security and the safe, sustainable use of radiation sources. SNM, including plutonium and highly enriched uranium, pose significant risks if misused, potentially leading to improvised nuclear devices. Additionally, the illicit trafficking of radioactive materials raises concerns regarding their malicious use in radiological dispersion devices (e.g., "dirty bombs") and radiological exposure devices, with highly disruptive social, economic, and psychological consequences. Effective control of radiation sources throughout their lifecycle—”from cradle to grave”—requires stringent oversight, especially at borders, airports, and seaports. While radiation monitoring portals (RPM), are essential to detect and monitor gamma and in some cases neutron radiation, their high cost and limited applicability present challenges in preventing the trafficking of radioactive sources and materials.
This study details the development and optimization of a radiation detection system designed for security and defense applications, characterized by short source-to-detector distances and the presence of hidden sources. The developed system, employing EJ-200 and EJ-426HD scintillators coupled with Silicon Photomultipliers (SiPM), simultaneously detects gamma/beta radiation and neutrons. Tailored for use with Unmanned Aerial Vehicles (UAV), the system is compact, lightweight, and cost-effective, validated through Monte Carlo simulations, laboratory experiments, and field tests. Key results of the work performed are summarized below:
(i) Development of a compact portable neutron detection system: The system employs an EJ-426HD scintillator coupled with SiPM and high-density polyethylene (HDPE) neutron moderators to detect both thermal and fast neutrons. The addition of HDPE moderator plates around the detector enhanced detection efficiency while minimizing gamma radiation sensitivity—a critical factor in avoiding false positives;
(ii) Optimization and comparison of EJ-200 scintillator with a CsI(Tl) scintillator: Measurements with a 137Cs source at distances ranging from 1 to 5 meters demonstrated that the EJ-200 scintillator exhibited a gamma detection efficiency approximately three times higher than CsI(Tl);
(iii) Integration of the detection system into an UAV for maritime container inspections: The system was integrated into a UAV multi-rotor platform for inspecting 20-foot-long maritime shipping containers. During a field inspection, the system successfully detected and localized 137Cs sources (4 MBq) and neutron sources (1.45 GBq 241Am-Be) within the container, demonstrating its effectiveness in real-world conditions;
(iv) Informative path planning algorithms based on profit functions were developed, enabling the detection system to dynamically adjust the inspection path based on real-time information about the source's location. The algorithms used either source position estimates, obtained through Maximum Likelihood Estimation (MLE) or real-time count data to adjust the UAV path, optimizing the inspection process. The use of a set of parameters to indicate the source position estimation confidence (exit condition), allowed to reduce the inspection time while maintaining a high accuracy in the localization of 137Cs sources, within 0.6 m for an Up and Down (UD) profit function (performs a vertical scan to the container when a hot spot is detected) and within 0.4 m for “Step and UD” (STUD) profit function (performs a sinusoidal movement when a certain threshold is achieved). The STUD profit function also minimized inspection time, reducing it to under 45 seconds. This capability represents a significant advancement over traditional manual and fixed inspection methods;
Other methods are described in literature to detect and localize radiation sources in urban areas, such as:
(i) Fixed Detector Networks, by using several stationary detectors spatially distributed (unpracticable for large areas such as a seaport);
(ii) Portable RPM (limited use due to lack of mobility); and
(iii) Mobile radiation detection systems composed by large and heavy radiation detection systems transported by cars or vans.
The developed detection system can be carried by small mobile platforms such as multi-rotors and provides a cost-effective alternative or complement to traditional RPM, fixed detector networks, and mobile radiation detection systems based on large radiation detection systems. It also provides an alternative to manual inspections, which are performed every time an alarm is triggered at a RPM, thus reducing significantly the secondary inspection times (which can take up to 20 minutes per container in ports) and avoiding the need for physically opening containers to inspect cargo.
Some system advantages and contributions of the portable detection system offers several advantages: it is lightweight, cost-effective, and integrates into UAVs or other mobile platforms (land, maritime, or hybrid). It efficiently detects gamma/beta radiation and neutrons, accurately locates gamma radiation sources, reduces the risk of false positives, and can detect SNM and other neutron sources like 252Cf and 241Am-Be. The main features of the developed radiation detection system encompass:
(i) The development of a portable radiation detection system with enhanced detection efficiency and modular neutron detection capabilities;
(ii) The Integration of SiPMs to reduce system size and weight, facilitating its use in mobile platforms with payload constraints;
(iii) The Creation of data processing algorithms for real-time operation, allowing the system to perform autonomously or with mobile platforms;
(iv) The introduction of informative path planning to optimize the detection process and reduce inspection time.
The impact of cargo material, such as plastic, aluminium and lead (radiation attenuation) in the source detection outside the container will also be addressed using the state-of-the-art Monte Carlo software program Monte Carlo N-Particle (MCNP).
Future work will enhance the detection system position accuracy measured at each instance by using more advanced GNSS receivers with inertial measurement unit (IMU) or real-time kinematic GNSS, testing multiple sources, and adapting the technology for other applications, such as nuclear forensics, nuclear facility inspections or post-radiological accident surface mapping.
In conclusion, the developed system represents a significant advancement in radiation detection technology, offering a practical and efficient solution for detecting and localizing illicit nuclear materials and radiation sources in a variety of security scenarios. The possible system's integration into an UAV platform and the use of informative path planning based on profit functions and real-time data provide an innovative approach to radiation monitoring.
