The Naval Surface Warfare Center Dahlgren Division serves as the executive agent for the DoD's Contraband Detection and Cargo Container Inspection Technology Development Program. The goal of the DoD non-intrusive inspection (NII) program is to develop prototype equipment that can be used to inspect containers and vehicles, quickly and in large numbers without unnecessary delays in the movement of legitimate cargo. This paper summaries the past accomplishments of the program, current status, and future plans.

Nuclear based techniques, and among them the neutron based ones, provide two essential ingredients for effective substance detection, ability to detect and recognize as many signatures of the relevant chemical elements as possible (i.e., high specificity) and to do it on as small as possible volume of the interrogated object (i.e., imaging capabilities). Various techniques and their imaging capabilities, implementation and proper applications are reviewed. Active techniques based on thermal neutron capture (TNA) and fast neutron (mostly) inelastic scattering in various temporal regimes: steady state, slow (microsecond) and fast (nanosecond) pulsing is reviewed. Neutron resonance attenuation (NRA) based techniques also are discussed and evaluated within the envelope of existing and future applications.

The increase in international terrorist activity over the past decade has necessitated the exploration of new technologies for the detection of plastic explosives. Quadrupole resonance analysis (QRA) has proven effective as a technique for detecting the presence of plastic, sheet, and military explosive compounds in small quantities, and can also be used to identify narcotics such as heroin and cocaine base. QRA is similar to the widely used magnetic resonance (MR) and magnetic resonance imaging (MRI) techniques, but has the considerable advantage that the item being inspected does not need to be immersed in a steady, homogeneous magnetic field. The target compounds are conclusively identified by their unique quadrupole resonance frequencies. Quantum magnetics has develop and introduced a product line of explosives and narcotics detection devices based upon QRA technology. The work presented here concerns a multi-compound QRA detection system designed to screen checked baggage, cargo, and sacks of mail at airports and other high-security facilities. The design philosophy and performance are discussed and supported by test results from field trials conducted in the United States and the United Kingdom. This detection system represents the current state of QRA technology for field use in both commercial and government sectors.

Piezo-electric ringing (PER) has been demonstrated to be an effective means of scanning cargo for the presence of hidden narcotics. The PER signal is characteristic of certain types of crystallized material, such as cocaine hydrochloride. However, the PER signal cannot be used to conclusively identify all types of narcotic material, as the signal is not unique. For the purposes of cargo scanning, the PER technique is therefore most effective when used in combination with quadrupole resonance analysis (QRA). PER shares the same methodology as QRA technology, and can therefore be very easily and inexpensively integrated into existing QRA detectors. PER can be used as a pre-scanning technique before the QRA scan is applied and, because the PER scan is of a very short duration, can effectively offset some of the throughput limitations of standard QRA narcotics detectors. Following is a discussion of a PER detector developed by Quantum Manetics under contract to United States Customs. Design philosophy and performance are discussed, supported by results from recent tests conducted by the U.S. Drug Enforcement Agency and U.S. Customs.

The use of nonintrusive inspection systems for contraband detection at border crossings has fostered a need for assessment of current performance in order to better direct future development of these technologies. The similarities between the nondestructive detection of flaws in engineered structures and the nonintrusive detection of contraband at border crossings provides the underlying rationale for the use of the probability of detection (POD) concepts already developed for aerospace and medical applications. This paper outlines the application of these POD concepts to the border crossing scenario, and includes a discuss and demonstration of applicable POD concepts and methods to a representative problem.

A fusion of two independent but complementary three- dimensional imaging techniques is proposed for detecting drugs in containers, cargo, mail and luggage. The containers, cargo, mail and/or luggage are scanned using a combined neutron and gamma ray source. A detector that can detect both neutrons and gamma rays is used to produce three dimensional images from both signals. The two images will be combined and analyzed by a fast host computer to detect drugs that may be concealed in the container, cargo and/or luggage. The two independent signatures from both neutrons and gamma rays, when analyzed simultaneously, may help determine the type of concealed material inside the containers. Containers, cargo and luggage are filled with a large variety of materials. Imaging them only in two dimensions may result in a poor contraband detection probability as different materials may shield each other. Therefore, a true three-dimensional imaging system is proposed, where the individual items inside the container or cargo can be resolved. This is expected to lead to reliable identification of the drugs even in small quantities. Such a system will also pinpoint the location of the suspected item and help expedite inspection by law enforcement agents. The proposed detection system produces two complementary three- dimensional images of the containers, cargo and/or luggage. These images are combined and analyzed by a specially developed algorithm to identify and locate the contraband automatically.

We describe a nuclear technique, the carbon camera, with which we have produced images of elemental carbon in concentrations and with surface densities typical in kilo quantities of narcotics. The signal is all high-energy gamma rays detected in a short time interval after irradiation of a target pixel by photons produced with an electron beam. Our carbon marker, the photoproton reaction on the minority carbon isotope, gives a robust signal with no interfering signals. We describe here the physics of the carbon camera and sketch our efforts to develop the technology of a fieldable instrument.

A non-intrusive, passive technique for the inspection of large cargo containers for plant contraband was investigated. The method is based on the detection of naturally occurring K-40 gamma-ray emissions. The results of preliminary dynamic field tests conducted at a Canada-US border-crossing using plastic and sodium iodide detectors are reported. Speed normalized results obtained from a wide range of cargo trucks, including controls carrying known amounts of a K-40 simulant, were used in discerning the presence or absence of K-40 emissions. A multi-component feature analysis method for the classification of cargo contents was investigated.

The pulsed fast neutron analysis (PFNA) cargo inspection system (CIS) uses a nanosecond pulsed beam of fast neutrons to interrogate the contents of small volume elements -- voxels -- of a cargo container or truck. A color display shows the three-dimensional location of suspected contraband, such as drugs or explosives. The neutrons interact with the elemental contents of each vowel, and gamma rays characteristic of the elements are collected in an array of detectors. The elemental signals and their ratios give unique signatures for drugs and other contraband. From the time of arrival of the gamma rays, the position of the vowel within the truck is determined. The PFNA CIS is designed to scan five or more trucks per hour. The operator interface has been designed to assist in the rapid identification of drugs, explosives or other contraband. This paper describes the system and the tests for drugs and explosives that have been carried out during the past year. These tests were aimed at exploring the envelope of performance of the system.

This paper describes the application of thermal neutron analysis (TNA) to a variety of non-intrusive detection problems. TNA is based on the analysis of neutron capture gamma rays from particular elements which are indicative of the material of interest. TNA was developed for detection of concealed explosives in airline luggage during the late 1980s and is now being investigated and tested for new applications. These applications include detection of drugs in passenger luggage, detection of explosives and drugs in small packages, detection of liquid explosives in bottles, and detection of buried land mines and unexploded ordnance. For explosive, land mine and UXO detection, the TNA is based on the 10.8 MeV capture gamma ray from nitrogen, whose high density is uniquely characteristic of modern high explosives. For detection of drugs, the use of capture gamma ray signals from both hydrogen and chlorine (from hydrochloride drug salt) have been investigated, and a specific set of features based on these gamma ray signals selected for the detection algorithm. The research and test results of this wider application of TNA, carried out over the last year are described.

A compact integrated narcotics detection instrument (CINDI) has been developed at NOVA R&D, Inc. with funding provided by the U.S. Coast Guard. CINDI is designed as a portable sensitive neutron backscatter detector which has excellent penetration for thick and high Z compartment barriers. It also has a highly sensitive detection system for backscattered neutrons and, therefore, uses a very weak californium-252 neutron source. Neutrons backscatter profusely from materials that have a large hydrogen content, such as narcotics. The rate of backscattered neutrons detected is analyzed by a microprocessor and displayed on the control panel. The operator guides the detector along a suspected area and displays in real time the backscattered neutron rate. CINDI is capable of detecting narcotics effectively behind panels made of steel, wood, fiberglass, or even lead-lined materials. This makes it useful for inspecting marine vessels, ship bulkheads, automobiles, structure walls or small sealed containers. The strong response of CINDI to hydrogen-rich materials such as narcotics makes it an effective tool for detecting concealed drugs. Its response has been field tested by NOVA, the U.S. Coast Guard and Brewt Power Systems. The results of the tests show excellent response and specificity to narcotic drugs. Several large shipments of concealed drugs have been discovered during these trials and the results are presented and discussed.

A neutron transmission spectrometer, the multi-dimensional neutron radiometer (MDNR) has been used to determine the presence of contraband substances in sealed containers. A pulsed 'white' neutron source was created by allowing a pulsed beam of 5.5 MeV deuterons to impinge on a thick beryllium target. The neutron intensity was measured from about 0.75 MeV to about 4 MeV, first with the sample out of the beam and then with the sample in the beam, to determine the neutron attenuation. Both collimated beam and cone beam geometries were employed. The collimated beam experiments have been used to determine the presence of contraband with a high degree of accuracy. The present work describes a neural network computer simulation and real-time data reduction program for contraband detection using neutron transmission.

A vehicle and cargo inspection system (VACIS) is described wherein fast-screening is achieved at low cost in a trade- off between cost, speed, resolution, reliability, transportability and power requirements. In its initial configuration, VACIS utilizes a shuttered Cs-137 source and a detector tower, or linear array, that travel along the cargo vehicle on trolleys that are moved by a common-source, variable-speed, synchronous motor drive. In another configuration, presently under development, the vehicle (such as a train) moves past the source and detector at both creeping and very high variable speeds. The variable velocity is constantly measured and is used as input to the image-generating program to produce undistorted gamma radiographs at 0.5 to 60 mph or more.

A mobile, rapid-deployment, x-ray system for the inspection of vehicles and freight containers has been developed and delivered in a prototype configuration. The system is based on 450 kV flying-spot x-ray beam technology originally developed for inspection of commercial vehicles at fixed- site border crossings and ports. The fixed-site system includes both transmission and Compton backscatter imaging capabilities. The prototype mobile system employs backscatter imaging only, which allowed it to be brought into service sooner and at lower cost, while still achieving most of the functionality and detection capabilities of a full system. Work is in progress to incorporate transmission imaging. Both the primary radiation dose and the environmental dose due to leakage and scatter are low. Measured primary and secondary radiation exposure rates are presented. The prototype system was configured and certified as a 'cabinet' x-ray system. The pros and cons of this certification compared to alternative 'industrial' certification is discussed. The mobile vehicle/ cargo inspection system is typically deployed and operated by a crew of three. Deployment requires about 10 minutes after its arrival on-site. During acquisition of scan data, a slow-speed hydraulic drive system moves the inspection system past the inspected object at a speed of 6 inches per second. Smaller vehicles (less than about 6 feet in height) can be scanned in a single pass for each side; taller vehicles require multiple scans for full coverage. Sample backscatter images obtained during system tests are presented.

The technology of transmission and backscatter imaging by flying-spot x-ray beams was extended to 450 kV beam energies with the installation of a prototype CargoSearch^TM system at Otay Mesa, California in the summer of 1994. CargoSearch^TM is a fixed-site system designed for the inspection of large over-the-road vehicles at border crossings. A self-contained, mobile implementation of the same technology has also been developed to scan objects ranging in size from a small car up to a full-scale tractor- trailer rig. MobileSearch^TM is able to be moved over ordinary roadways to its intended operating site and set up easily by two or three people, but is currently limited to backscatter imaging only. It also lacks the ability to effectively image the vehicle's undercarriage, which is important for the detection of contraband concealed in the vehicle itself rather than its cargo. There is a need for a transportable, deployable scanning system that combines the self-contained mobility of MobileSearch^TM and the combined transmission and backscatter imaging characteristics of CargoSearch^TM, including its good geometry for backscatter imaging of the undercarriage of inspected vehicles. Concepts for two approaches that meet these needs are presented.

The certification of CTX 5000 by the U.S Federal Aviation Administration (FAA) as an explosives detection system (EDS) roughly coincided with the first commercial installation of CTX 5000 at an operational airport. Since then, more than twenty CTX 5000 SPs have been installed and operated around the world. The explosion of TWA Flight 800 in July 1996 has put the spot light on CTX 5000 again. By now InVision has gained sufficient experience from CTX 5000 deployments at various airports to allow its speedy integration at any airport, with regards to the specific needs of each site. The paper discusses examples of the alternative installation configurations, the issues involved, and the experience gained.

This paper describes the design, physical properties, and field experience with image-quality indicators or plaques that have been used for the baseline assessment of x-ray systems for the detection of contraband in small packages. Plaques have been developed and used in the baseline assessment of transmission, backscatter, and computed tomography systems.

The DoD Counterdrug Technology Development Program has addressed the development and demonstration of technology to enhance nonintrusive inspection of small packages such as passenger baggage, commercially delivered parcels, and breakbulk cargo items. Within the past year they have supported several small package-class nonintrusive inspection system performance assessment activities. All performance assessment programs involved the use of a red/blue team concept and were conducted in accordance with approved assessment protocols. This paper presents a discussion related to the systematic performance assessment of small package-class nonintrusive inspection technologies, including transmission, backscatter and computed tomography x-ray imaging, and protocol-related considerations for the assessment of these systems.

A prototype for explosives detection based on CXRS (coherent x-ray scattering) has been developed within a Philips research project, funded in part by the German Ministry of the Interior (BMI). The system uses primary x-radiation from a high power x-ray tube (160 kV) to generate coherent scatter which is measured at a small fixed angle in the forward direction. Scatter spectra from many volume elements ('voxels') of a piece of luggage are accumulated with an energy-resolving multi-channel germanium detector. For most military and industrial explosives, the scatter spectra exhibit characteristic diffraction peaks corresponding to their polycrystalline structure. The technique thus lends itself to a fully automatic inspection process. The system is to be tested and refined during a test phase at Hamburg airport. Its principle, geometry and design are presented along with some results concerning CXRS material selectivity.

The use of scattered radiation in the production of signatures for explosive detection has been studied. Signatures have been measured and the spectral analysis of these using multivariate statistics has demonstrated that explosives within realistic environments can be recognized. The problem remains of how to use this information in the time frame allowed by airport baggage security checks. To address these problems we have developed a 'tuned' system approach. The energy-angle space diagrams have been created and the areas containing the greatest information density in the presence of an explosive have been identified. A specially designed detector (CdZnTe) array has been built to match these regions. The array has been used to identify explosives hidden within realistic case situations.

High-energy monoenergetic gamma rays (6.13 and 7.12 MeV) from the decay of excited states of the ¹⁶O* nucleus are highly penetrating and thus offer potential for non- intrusive inspection of loaded containers for narcotics, explosives, and other contraband items. These excited states can be produced by irradiation of water with 14-MeV neutrons from a DT neutron generator or through the ¹⁹F(p,alpha)¹⁶O* reaction. Resonances in ¹⁹F(p,alpha)¹⁶O* at proton energies between 340 keV and 2 MeV allow use of a low-energy accelerator to provide a compact, portable gamma source of reasonable intensity. The present work provides estimates of gamma source parameters and suggests how various types of contraband could be detected. Gamma rays can be used to perform transmission or emission radiography of containers or other objects. Through the use of (gamma,n) and (gamma,fission) reactions, this technique is also capable of detecting special nuclear materials such as deuterium, lithium, beryllium, uranium, and plutonium. Analytic and Monte Carlo techniques are used to model empty and loaded container inspection for accelerator-produced gamma, radioisotope, and x-ray sources.

This paper investigate, with the aid of Monte Carlo simulations and laboratory experiments, a technique for the detection of narcotics in large cargo containers using gamma-radiation. The transmission and back-scattering of photons, at different energies, is used to provide information useful for identifying the presence of bulk quantities of commonly encountered narcotics.

The use of multivariate calibration for the real time analysis of energy dispersive x-ray scatter profiles is being investigated. The requirements of a practical baggage scanner necessitate rapid interrogation and an analysis procedure is required that can differentiate between spectral structure in diffraction profiles in very noisy data. Multivariate analysis has been successfully used to identify sheet explosives in cases with acquisitions as low as several hundred counts. Two detector systems, a high resolution HPGe detector and a room temperature CdZnTe detector, have been used. The precision of the model predictions are highly dependent upon the detector system used producing a significantly smaller error with the high resolution detector.