Nuclear detection

Abstract: Countering clandestinely delivered nuclear and radiological threats requires a multielement, global, civil/military, system-of-systems approach. One important element is geographically layered, sensor-based detection of threat objects, including radiation detection systems. An effective defense against these threats should take advantage of the latest developments in radiation detection technology. This paper reviews the physics of nuclear detection, and points out areas where improvements can be anticipated, via case studies of technologies such as gamma-ray imaging, advanced radiography, large-area detectors, and active interrogation.

Abstract: A nuclear detection system and method uses an artificial neural system to efficiently detect explosives in checked airline baggage or other parcels with a high probability of detection (PD) and a low probability of false alarms (PFA). The detection system detects the presence of nitrogen and other elements and their rough density distribution within the object under investigation by performing a nuclear-based analysis of the object. The detection system includes a source of neutrons; an array of gamma ray detectors; at least one neutron detector; means for irradiating the object being examined with neutrons from the neutron source, which neutrons interact with the atomic nuclei of one or more specific elements, e.g., nitrogen, chlorine, or hydrogen present within the object so as to cause elemental-specific gamma rays to be emitted; means for capturing and counting the elemental-specific gamma rays and determining their approximate origin within the object, thereby providing a rough measure of the density distribution of these specific elements within the object; and means for detecting neutrons that pass through the object without substantially interacting with atomic nuclei, thereby providing an image of the density distribution of elements in the object. The invention further includes an X-radiography system for generating a high-resolution two-dimensional density image of the object. An artificial neural system (ANS) provides an efficient means for analyzing the recorded gamma rays, image, and other data so as to accurately discriminate between objects carrying explosives and objects not carrying explosives.

Abstract: The timely and accurate detection of nuclear contraband is an extremely important problem of national security. The development of a prototype sequential Bayesian processor that incorporates the underlying physics of ?-ray emissions and the measurement of photon energies and their interarrival times that offers a physics-based approach to attack this challenging problem is described. A basic radionuclide representation in terms of its ?-ray energies along with photon interarrival times is used to extract the physics information available from the uncertain measurements. It is shown that not only does this approach lead to a physics-based structure that can be used to develop an effective threat detection technique, but also motivates the implementation of this approach using advanced sequential Monte Carlo processors or particle filters to extract the required information. The resulting processor is applied to experimental data to demonstrate its feasibility.

Abstract: A large area nuclear detection system with high resolution includes a sensor formed of scintillating optical fibers and a remotely located detector comprising at least a pair of microchannel plate photomultiplier tubes, with the sensitive area of the sensor being many times the area of the detectors. Two linear arrays of optical fibers are arranged orthogonally to define a sensor matrix of rows and columns of fibers. Nuclear radiation from a particle at the sensor is converted to optical energy by the sensor. A microchannel PMT is connected with each array for measuring the optical energy output of the fibers thereof to determine the row and column location of the nuclear particle in accordance with the quantity of energy received from the fibers. Thus, nuclear radiation can be detected over a large area with a high degree of accuracy and resolution. A characterizing feature of the detection system is the conversion of the output of large orthogonally arranged layers of scintillator elements from a long and narrow rectangular format to a square or round output format to match the detector which typically has round or square sensitive areas of a few centimeters.