Homeland Security and Contraband Detection
Detection of contraband and illicit materials has become increasingly important, especially since the terrorist attacks in the United States on September 11, 2001. The nature of the detection problem embodies both physics issues and a set of operational constraints that limit the practical application of neutrons. The issue under consideration is detection of materials that are considered serious threats; these may include explosives; radioactive materials, fissile materials, and other materials associated with nuclear weapons, often referred to as special nuclear material (SNM). The overriding constraint is in the physics: systems must be based on clean physics; but unlike physics experiments, detection systems work under the limitation that materials must be identified nonintrusively, without interrupting the normal flow of commerce and with a high probability of detection and a low probability of false alarms. A great deal of work has been reported in the literature on neutron-based techniques for detecting explosives and drugs. The largest impetus by far for detecting explosives comes from aviation industry requirements for inspecting luggage and, to a lesser extent, cargo. The major alternative techniques are either X-ray–based or chemical trace detection methods that look for small traces of explosive residues. The limitations of the X-ray and trace methods in detecting explosives are well known, but currently (2008) it is safe to say that no neutron- or nuclear-based technique is being used routinely for security inspection, despite extensive development of these methods. Smuggling of nuclear materials has become a concern, and neutron techniques are particularly attractive for detecting them. Given the limitations of X-ray techniques and the need for SNM detection, it is now useful to reexamine neutron methodologies, particularly imaging. A significant number of neutron-based techniques have been proposed and are under development for security applications, especially SNM detection, but describing how they work is beyond the scope of the chapter. Instead, one particular approach to neutron imaging, neutron resonance radiography (NRR), is discussed in detail as it illustrates many of the issues connected with imaging and detection.
KeywordsNeutron Technique Nuclear Weapon Neutron Cross Section Fissile Material Neutron Imaging
The work on NRR was a collaboration between the MIT Department of Nuclear Science and Engineering, the MIT Laboratory for Nuclear Science, L3-Communications, and LLNL. The author especially thanks David Perticone (L-3), who was the principle investigator on the NRR project and was responsible for much of the progress made on it, as well as Vitalyi Ziskin (L-3 and MIT), Gongyin Chen (L-3 and Varian), Whitney Raas (MIT), and Gordon Kohse (MIT) for their contributions throughout the project. Jim Hall (LLNL), Brian Rusnak (LLNL), and John Watterson (University of the Witwatersrand) made invaluable contribution in the early parts of the project.
Others include the staff of the MIT-Bates Laboratory for their excellent contributions to the construction and operation of the NRR prototype, especially Bob Fisk, Peter Binns, Jim Kelsey, Peter Goodwin, Christoph Tschalaer, and Jan Van Der Laan; and the following engineering staffs of L-3 Communications for the design of system components: Tim Hart, Ken Prather, Jim Karon, Tony Antoniou, John Price, Keith McClelland, Brain Pearson, Steve McDevitt, Jeff Stillson, and Sal Gargiulo.
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