# State-of-the-Art Mobile Radiation Detection Systems for Different Scenarios
###### Abstract  
In the last decade, the development of more compact and lightweight radiation detection systems led to their application in handheld and small unmanned systems, particularly air-based platforms. Examples of improvements are: the use of silicon photomultiplier-based scintillators, new scintillating crystals, compact dual-mode detectors (gamma/neutron), data fusion, mobile sensor networks, cooperative detection and search. Gamma cameras and dual-particle cameras are increasingly being used for source location. This study reviews and discusses the research advancements in the field of gamma-ray and neutron measurements using mobile radiation detection systems since the Fukushima nuclear accident. Four scenarios are considered: radiological and nuclear accidents and emergencies; illicit traffic of special nuclear materials and radioactive materials; nuclear, accelerator, targets, and irradiation facilities; and naturally occurring radioactive materials monitoring-related activities. The work presented in this paper aims to: compile and review information on the radiation detection systems, contextual sensors and platforms used for each scenario; assess their advantages and limitations, looking prospectively to new research and challenges in the field; and support the decision making of national radioprotection agencies and response teams in respect to adequate detection system for each scenario. For that, an extensive literature review was conducted. mobile radiation detection systems; NORM; radiological emergencies; nuclear accidents; illicit trafficking accelerators; targets and irradiation facilities; gamma and neutron detectors 2021  
212105111051  
According to the International Atomic Energy Agency (IAEA) [2], between 1993 and 2019, a total of 3686 incidents, of which 290 involved a confirmed or likely act of trafficking or malicious use, are reported in the illegal traffic database. Other incidents reported in the IAEA database related to safety and security issues associated to radioactive materials involve, inter alia, theft or loss of radioactive sources, unauthorized disposal (sources entering the scrap metal industry), unauthorized shipment of contaminated scrap metal, and the discovery of radioactive sources (orphan sources, out of regulatory control). Radiation portal monitors (RPM) are often used for the prevention of illicit traffic of SNM and radioactive materials, as well as the inadvertent movement of radioactive material. They are located at appropriate checkpoints (e.g., border crossings, airports and seaports) to measure gamma and neutron radiation. Other radiation detection equipment are personal radiation detectors (PRDs) used by front line officers (FLO), hand-held gamma and neutron search detectors, and hand-held radionuclide identification devices. Hand-held instruments can be used as primary detection systems (greater flexibility), or as a secondary search device, for example, to validate a reading from an RPM or PRD [3]. Due to the many potential entryways or transportation modes in a country [4] and inherent difficulty to detect such materials, particularly SNM (normally weak sources, possibly shielded or masked) [5], it is necessary to improve the detection probability to reduce the wrongdoer's success. The use of portable radiation portal monitors (PRPM), helped to mitigate the lack of devices in other strategic points (depending on the potential threats). Since the a priori location of the PRPMs is unknown, it has also a deterrence effect on potential terrorist acts. However, the \"portability\" of these devices only means that they can be disassembled into a case for the subsequent transport. The PRPM are normally made with plastic scintillation detectors and can also be used for RN accidents and emergencies (people and vehicles monitoring) [6].