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The scope and applicability of detecting gamma-emitting materials by first responders and advanced searchers have changed considerably over the last 15 years. More often than not the searchers are being asked to obtain an image of the gamma sources that are shielded or otherwise inaccessible. They are constantly being tasked to localize a moving source in busy traffic. Commercially available gamma detection units and prototype Government-funded research products use complex techniques such as hybrid imaging processes (combination of traditional Compton imaging with coded aperture masks, for example, modified uniformly redundant array [MURA] patterns). Standalone radiation detection systems are increasingly capitalizing on multi-modal detection, emphasizing on data fusion, informatics, and novel signal/signature exploitations. At the request of the U.S. Department of Homeland Security (DHS) Countering Weapons of Mass Destruction (CWMD) Office, previously known as the Domestic Nuclear Detection Office (DNDO), a study committee from the American Physical Society has recommended that emphasis is kept on the ability to detect shielded special nuclear material with high sensitivity and reliability. Development of new and improved detection algorithms (e.g., principal component analysis, maximum-likelihood estimation algorithm, and others) has been encouraged. CWMD has been urged to focus on signature identification in its nuclear forensic portfolio. Newer materials like SrI3:Eu2+, LaBr3:Ce, CeBr3:Ca2+ with fast rise time and short decay time of gamma pulses, high intrinsic gamma sensitivity, high gamma energy resolution, and high-efficiency conversion of excitation energy to fluorescent radiation are constantly being sought to build gamma detectors. Neutron detection and associated activation analysis using a gamma ray detection system is highly encouraged. There is a constant demand for miniaturization of gamma radiation detection system for tactical usage in the field– the most sought-after device must be lightweight, easy to use, should be able to withstand harsh environmental conditions, long shelf life with commensurate long battery life, high sensitivity (with preferably high resolution), capable of creating flexible and configurable alarm conditions with directional sensitivity. This array of technical constraints demands stringent specifications on the readout electronics, data acquisition technologies, interoperability and interconnectivity of data output and strict quality assurance of the detection and measurement devices. In recent years the CWMD has developed a system called Intelligent Radiation Sensing System (IRSS) that harnesses the information gathered by ubiquitous radiation monitoring systems deployed by the state, local, and tribal law enforcement organizers [1]. The IRSS was created to better equip law enforcement entities to protect large cities from the threats and harmful effects of nuclear or radiological incidents and emergencies. The IRSS uses a breakthrough technology that networks a group of portable radiation detectors with improved detection, localization, and identification of potential radiological threat. The program created a robust, flexible network architecture along with advanced data fusion algorithms that combine information from many detectors. A study [2] published in the Journal of Materials Research summarized the basic requirements for materials to be used in development of scalable radiation detection systems that considered the critical material performance metrics of energy resolution (1% for semiconductors like CZT |
