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1 Introduction Since the release of the widely publicized reports of the White House Commission on Aviation Safety and Security (1996, 1997)—which recommended the deployment of ''significant numbers of computed tomography detection systems, upgraded x-rays, and other innovative systems"—the Federal Aviation Administration (FAA) has deployed 631 FAA-certified explosives-detection systems (EDSs),2-4 four noncertified bulk-explosives detection devices, and more than 300 trace explosives-detection devices. To date, all of the FAA-certified EDSs employ an x-ray-based computed tomography (CT) detection methodology. However, through its Explosives Detection Program, the FAA continues to pursue research in other promising technologies for addressing the FAA's future needs for explosives detection. Overview of Pulsed Fast Neutron Transmission Spectroscopy One area of research the FAA has pursued is accelerator-based nuclear detection technologies that detect explosives by measuring the elemental composition of materials. These technologies exploit the high nitrogen and oxygen content found in most explosives. Pulsed fast neutron transmission spectroscopy (PFNTS) identifies explosives by the specific material- and energy-dependent absorption and scattering cross sections of neutrons interacting with the nuclei of different elements. PFNTS can determine the hydrogen, carbon, nitrogen, and oxygen content in an object, and the relative amounts of these elements can be used to discriminate explosive from nonexplosive materials. PFNTS also has the potential to generate low-resolution tomographic images (NRC, 1998; Overley, 1987). PFNTS also has a number of practical limitations, including large size and weight, the need for radiation shielding, and regulatory and safety issues associated with nuclear-based technologies (NRC 1993, 1997). Background of This Study In 1993, the FAA requested that the National Research Council (NRC) assist the agency in assessing its explosives-detection program. The NRC responded to this request by convening the Committee on Commercial Aviation Security (CCAS). Since 1993, the committee has produced two interim reports (NRC, 1996, 1997) that provided recommendations for structuring the FAA's research portfolio for the explosives-detection program, including bulk explosives detection, explosives trace detection, combined technologies, and human factors. In the second interim report (NRC, 1997), the CCAS recommended that the FAA should not pursue accelerator-based technologies for the primary screening of checked baggage or fund the development of any large accelerator-based hardware (see Box 1-1). The CCAS concluded that the detection performance of an explosives-detection method should be well understood before airport integration issues are addressed (NRC, 1997). Recent testing had indicated that, with the exception of Class A5 explosives, the detection performance of PFNTS was con- 1 The FAA intends to deploy 74 certified explosives-detection systems by March 1999. 2 The following terminology is used throughout this report. An explosives-detection device is an instrument (not FAA certified) that incorporates a single detection method to detect one or more category of explosives. An explosives-detection system (EDS) is a self-contained unit composed of one or more integrated devices that has passed the FAA's explosive-detection certification test. Explosives-detection equipment is any equipment, certified or not, that can be used to detect explosives. 3 Explosives-detection equipment includes any explosives-detection device or system that remotely senses some physical or chemical property of an object under investigation to determine if it is an explosive. Trace explosives-detection equipment requires that particles or vapor from the object under investigation be collected and identified. 4 In this report, explosives include all forms and configurations of an explosive at threat level. 5 Class A and Class B explosives are categories devised by the panel and do not represent a designation made by the FAA. PFNTS has difficulty detecting certain types and configurations of explosives defined as Class A explosives in this report. Class B explosives include all other explosives in the FAA's certification test set. A detailed description of Class A and Class B explosives is not available in this report due to the sensitive nature of this information. Specific questions regarding the performance of PFNTS should be addressed to the FAA.
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BOX 1-1 CCAS Recommendations for Accelerator-Based Explosives-Detection Technologies Recommendation 4-1. Do not consider accelerator-based technologies to have promise for deployment as a primary screening procedure for checked baggage inspection. Any screening procedure relying on an accelerator cannot compete with available technologies on either cost or practicality bases. Recommendation 4-2. Do not fund any large accelerator-based hardware development projects. Combinations of experimental work with existing laboratory equipment, mathematical modeling, and simulation can better define the potential of the nuclear technologies without the expense or time required to design and build new hardware. Source: NRC, 1997. sistent with the FAA EDS specification (Chmelik et al., 1997). In spite of this level of performance, the CCAS did not believe such a system should be fielded or even that optimal fielding configurations should be investigated. The committee concluded that testing should be conducted with existing laboratory systems and smaller pixel sizes to determine the detection limits of PFNTS for Class A explosives. Only if this testing demonstrated that the detection performance6 could be substantially improved should the FAA investigate the potential application of this technology. The CCAS observed that the principal advantage of PFNTS may be its potential for resolving alarms raised by a lower-cost, high-resolution, image-based explosives-detection device or system (NRC, 1997). In order to demonstrate this potential, more will need to be done than determining the detection performance on a cluttered bag set consistent with the bag set used in the current FAA EDS certification testing. The PFNTS false alarm performance would have to be determined for a set of bags that set off the alarms of the best conventional (non-nuclear) EDSs. In 1994, the FAA awarded Tensor Technology7 a two-year grant to build a multidimensional neutron radiometer (MDNR)8 airline security system, including transporting the system to a nuclear accelerator and testing it to determine its sensitivity for detecting explosives concealed in suitcases (Tensor Technology, 1998a). In these tests, the detection performance of the MDNR showed promise for meeting the probability of detection (Pd)required for FAA certification for all but one category of explosives. Considering these test results and the CCAS recommendations listed in Box 1-1, the FAA awarded Tensor a six-month cooperative agreement grant to present the company's evaluation of PFNTS compared to other, currently available technologies for the primary screening of passenger baggage for explosives and for the screening of cargo in airports. Tensor was asked to include the following points in its evaluation of PFNTS: operational requirements, including size, weight, power requirements, cooling, and other utility requirements, as well as placement options (bag room or a separate building away from public airport buildings) operational aspects, including operator training requirements, alarm resolution procedures, impact on air carrier operations, access to baggage, and baggage flow performance levels, including expected and measured detection and false alarm rates for all relevant types of explosives availability of equipment, including mean time between failures, mean time to repair, required parts inventory and lead time to obtain parts, and maintenance costs safety concerns, including radiation safety and monitoring, U.S. Nuclear Regulatory Commission licensing, and radiation shielding costs, including initial unit cost and installation costs, site preparation costs, costs of modifying belt lines and baggage-handling equipment and support equipment, and operational costs for utilities and environmental control cost to finish development compared to technical risk 6 In this context, substantial improvement involves achieving a high probability of detection while maintaining a low probability of false alarms. 7 Tensor Technology, Inc., Madison, Alabama. 8 Tensor Technology refers to their PFNTS-based explosives-detection device as a multidimensional neutron radiometer (MDNR) airline security system.
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BOX 1-2 Statement of Task for the Panel on Assessment of the Pulsed Fast Neutron Transmission Spectroscopy for Aviation Security The panel will evaluate the potential for pulsed fast neutron transmission spectroscopy for primary passenger baggage screening or cargo screening compared to currently available x-ray based computed tomography systems. To accomplish this the panel will: review and assess Tensor Technology's report, which is expected to address both technical and operational capabilities and projected capabilities of PFNTS for primary passenger baggage screening and cargo screening review the laboratory-demonstrated explosives-detection performance of PFNTS compare demonstrated and projected capabilities with those of currently available x-ray-based computed tomography systems evaluate the potential that end users will prefer a PFNTS-based system to currently available x-ray-based computed tomography systems outline any key assumptions that would be required to envision the use of PFNTS in airports and, if appropriate, recommend strategies to confirm these assumptions develop guidelines for the FAA to follow to determine the feasibility of PFNTS technology for use as explosives-detection equipment in airports The FAA requested that the NRC review and evaluate Tensor Technology's assessment of PFNTS in light of the previous recommendations of the CCAS (see Box 1-1) and in light of technical developments since the committee's second interim report. In response to the FAA's request, the NRC convened the Panel on Assessment of the Practicality of Pulsed Fast Neutron Transmission Spectroscopy for Aviation Security under the auspices of the CCAS. The panel was charged with evaluating the practicality of PFNTS for the primary screening of passenger baggage or for cargo screening, as compared to currently available x-ray-based CT systems (see Box 1-2). Organization of This Report This report assesses the practicality of PFNTS for aviation security. The principle of bulk explosives detection is discussed in Chapter 2. Chapter 3 contains an assessment of laboratory test results for PFNTS, and Chapter 4 discusses the laboratory and operational performance characteristics of the FAA-certified x-ray CT-based InVision CTX-5000.9 Tensor's report is reviewed in Chapter 5, and the panel's comparison of PFNTS and the CTX-5000 is presented in Chapter 6. The panel's conclusions and recommendations are presented in Chapter 7. 9 InVision Technologies, Newark, California.
Representative terms from entire chapter: