Modern trends in gamma detection systems for emergency response

Abstract

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, <3% for scintillators like LaBr3:Ce at 662 keV primary gamma ray energy from 137Cs isotope), fast timing including high mobility of electrons and holes in the semiconductors and fast scintillation processes, high spatial resolution for imaging purposes, high intrinsic detection efficiency (requiring high density, high effective atomic number Zeff), high geometric efficiency achieved sometimes by occlusion processes, neutron detection efficiency and operational factors like cost, ease of use, use of peripheral equipment like thermomechanical engines to stabilize the detection systems. Exciting new research and development work utilizing effective data mining algorithms is being performed at universities, national laboratories, and commercial institutions in gamma ray detection technology. For example, gamma ray imaging techniques first used in space telescopes are being applied in modern security and health systems in a joint project between the University of Southampton and industrial partner Symetrica. The project aims to develop a new coded aperture imaging system that could inspire a new generation of “stand-off” imaging systems. These systems would allow for remote inspection for radioactive materials. This review article intends to capture the synergy of international commercial collaborations exemplified by the United States Defense Advanced Research Projects Agency’s (DARPA’s) SIGMA program in which detector expertise originating from the United Kingdom (Kromek Group plc.) algorithm development and system modelling and analysis developed by United States national laboratories came together under the general guidance provided by a small commercial unit, Invincea Labs, in the area of network algorithm integration and development.