Sensitivity, specifity, high time resolution, and cost-effective simultaneous measurements of several components using operational systems are the main requirements for atmospheric research and air-pollution-monitoring instruments. Tunable diode lasers absorption spectroscopy is increasingly being used to measure atmospheric trace gas concentrations down to low ppb-levels (10^-9 volume mixing ratio). This optical technique fulfills the requirements for trace gas analysis in the atmosphere for most of the smaller molecules with resolved absorption spectra. Semiconductor lead salt diode lasers give access to the mid-IR spectral region, where the most important atmospheric constituents have strong rotational vibrational absorption bands. The application of high-frequency modulation (FM) schemes can further improve sensitivity and detection speed of modern instrumentation. With this technique, the absorption of a narrow spectral feature is measured by detecting the heterodyne beat signal that occurs when the balance of the FM optical spectrum of the laser is distorted by a molecular absorption line of the target gas. In this paper the FM technique will be reviewed and the predicted and current performance in terms of the detection limit will be discussed.

We are developing an imaging Fourier transform spectrometer for chemical effluent monitoring. The system consists of a 2D IR imaging array in the focal plane of a Michelson interferometer. Individual images are coordinated with the positioning of a moving mirror in the Michelson interferometer. A 3D data cube with two spatial dimensions and one interferogram dimension is then Fourier transformed to produce a hyperspectral data cube with one spectral dimension and two spatial dimensions. The spectral range of the instrument is determined by the choice of optical components and the spectral range of the focal plane array. Measurements in the near UV, visible, near IR, and mid-IR ranges are possible with the existing instrument. Gaseous effluent monitoring and identification measurements will be primarily in the `fingerprint' region of the spectrum, ((lambda) equals 8 to 12 micrometers ). Initial measurements of effluent using this imaging interferometer in the mid-IR will be presented.

The detection and identification of explosives in the field typically involves resolving the explosives from a multicomponent mixture. For an IR spectrometer system, the measured absorbance signals have to be deconstructed into the constituent absorbances produced by each explosive. Methods of multicomponent analysis are shown to be relevant to the quantitative determination of explosives concentration down to a lower detectable limit. Techniques of precise sample introduction with a vapor generator for explosives are used to reduce the error in the multivariate calibrations of the system. The performance of the IR spectrometer system was assessed on its ability to measure the absorbance at one wavelength for determining the concentration of RDX. It was determined to be 50 picograms for a signal-to-noise ratio of approximately 4. The results demonstrate that the system needs to be more rigorously tested with different sample mixtures of explosives and other commonly occurring components for a better multidimensional calibration of the system.

The FBI Laboratory has been involved in the development of new technology and in the innovative adaptation of existing technology for use in the war on drugs and terrorism. In the last 2 years the Laboratory has introduced 5 new tools into the FBI agent's technological arsenal for use in support of these investigations. The portable, simple-to-operate instrumentation includes a hand-held microwave dielectrometer, portable gas chromatograph, gas chromatograph/mass spectrometer, ion mobility spectrometer, and antibody-based field test kits. Real-world application of this new technology included detection of cocaine dissolved in 45 to 36,000 bottles of a beverage and cocaine molded in plastic fittings. Trace physical evidence from explosives can also be detected on hands and surfaces.

Representative samples for chemical detection can either be in the vapor or solid phase (trace particulate residues). In the CONDOR^TM contraband detection system the chemical detector is a tandem mass spectrometer that is programmable to measure the concentration in air of a variety of drug and explosive compounds. These measurements are done essentially simultaneously. The means of measuring air samples is straight forward since the contraband is already carried in vapor form in an air stream. However for particulate, a new front end module has been designed which thermally vaporizes the samples and entrains the resulting gases into a stream of hot air that is directed to the mass spectrometer ionization region. Due to the nearly instantaneous output of results, the sampling system is designated as the Real Time Sampler or more simply RTS. In this paper some of the design considerations and operational characteristics of the RTS will be discussed, including mechanical layout, timing, response times, desorption and transport system temperatures, contamination and memory- effect difficulties, as well as sensitivity and noise characteristics.

A new patented ion trap mobility spectrometer design is presented. Conventional IMS designs typically operate below 0.1% efficiency. This is due primarily to electrical-field-driven, sample ion discharge on a shutter grid. Since 99.9% of the sample ions generated in the reaction region are lost in this discharge process, the sensitivity of conventional systems is limited. The new design provides greater detection efficiency than conventional designs through the use of an `ion trap' concept. The paper describes the plasma and sample ion dynamics in the reaction region of the new detector and discusses the advantages of utilizing a `field-free' space to generate sample ions with high efficiency. Fast electronic switching is described which is used to perturb the field-free space and pulse the sample ions into the drift region for separation and subsequent detection using pseudo real-time software for analysis and display of the data. Many applications for this new detector are now being considered including the detection of narcotics and explosives. Preliminary ion spectra, reduced mobility data and sensitivity data are presented for fifteen narcotics, including cocaine, THC, and LSD are reported.

Barringer's new IONSCAN^TM model 350 provides improved operational flexibility, reliability, and effectiveness in the rapid on-site detection and identification of narcotics and explosives. The model 350 is a modular integrated design, with DC-power capabilities, and wheels or vehicle mounts to facilitate transportation to and operation in a variety of operational locations. Recent developments in IONSCAN ion mobility spectrometer (IMS) technology in the model 350 include a long-life air dryer/purification system and new software for improved substance detection and false alarm rate performance. New multiple peak detection capabilities for more reliable substance identification are described. Studies on IMS temperature and pressure effects are reported and their possible future use to further improve peak detection performance are discussed. Some recent applications in narcotics interdiction are described.

Methods of analyzing vapors in an IMS explosives/narcotics detector that is primarily designed for particle collection were investigated, with emphasis on nitroglycerin explosive, and acetic and benzoic acid contaminants in narcotics. A preconcentration step is required because expected vapor concentrations are low. NG adsorption and retention behavior on coated teflon filters that are compatible with the IMS sample desorption system is reported, including the effects of adsorbent, and sampling flow rate, time and volume. Similar investigations were carried out for acetic and benzoic acid vapors, and a gold-plated nickel mesh was selected as the most appropriate IMS-compatible filter for these materials. Vapor sampling flow rates and volumes are much lower than those used in particle sampling. Examples of NG and benzoic acid vapor detection in real and simulated applications are discussed.

This paper discusses the preparation to assess the performance of heroin and cocaine vapor/particle detection systems. Equipment available commercially and field prototype system equipment will be assessed. Breadboard or brassboard devices or prototype modules will not be assessed. The assessment comprises a performance specifications verification and target response and a controlled field test for equipment available commercially only. Special purpose test procedures, tools, and detection targets were developed to ensure the reproducibility and control of all assessment tests. The sampling equipment parameters and their relative importance and the test procedures and objectives were defined and designed to maximize the information obtained within the test constraints. Test results will be obtained for standardized fundamental representative targets, independent of detection strategy, which can be correlated to a wide range of applications by the potential users. United States Customs Service will not form conclusions regarding the equipment performance for specific applications. It is anticipated the utility of the assessment program will be in availing equipment standardized test results to law enforcement agencies to examine the compatibility of the equipment performance with their requirements, applications, and detection strategy.

Chemical detection techniques for explosive and illicit drug identification were originally directed towards the detection of vapors, with research groups aiming toward the specific target of creating a mechanical dog. With the advent of the mass spectrometry based contraband detection systems, exemplified by the CONDOR^TM which relies on both the detection of vapors and particles, research groups and instrument manufacturers changed direction and began to develop techniques mainly oriented toward the detection of trace particles. The major advantage to the use of trace particulate residues in the detection of hazardous material is that the actual substance can be identified in nearly all cases. On the other hand, as is discussed in detail in later sections of this document, sampling of complex items can be difficult. Both vapor and particulate sampling can be invaluable in the detection of hazardous materials. In many instances the techniques offer complementary information, and results obtained via one route may lead to the use of the alternative method (for example, the vapor detection of taggants as a screening technique followed by particulate analysis for the actual target). The concepts discussed in the remainder of this paper focus on the use of tandem mass spectrometry as an analytical device in the detection of contraband materials.

Forensic Laboratories performed qualitative analyses on the vapors above (head-space) seized cocaine samples during the period of 1986 - 1991. Thirty-two solvents were targets of the chemical head-space analyses. The results of the chemical analyses were statistically analyzed. The statistical analysis revealed trends in chemicals solvents being used or substituted for previously used solvents. This is critical to targeting the right chemicals for diversion control. In the 1991 head-space analyses, five chemical solvents could have been used as screening targets for cocaine contraband. The analysis showed strong trends in chemicals found. Routine statistical analysis of the head-space data will be needed to update the list of target screening chemicals.

To assist in combating the use of explosives by terrorists. Thermedics Detection has developed an Explosives Detection System named EGIS. This system is based upon high-speed gas chromatography coupled with a highly selective and sensitive chemiluminescence detector. EGIS has been deployed in numerous applications worldwide. Examples are given of the use of EGIS as part of a layered security system for screening carry-on baggage, checked baggage, vehicles, and mobile applications.

A review of data on narcotics and explosives particulates is presented. Methods to generate particles of narcotics and explosives will be discussed with respect to resulting particle size distribution and mass output. The application of these standards to the testing of narcotic and explosive particle detection systems will be addressed.

This paper discusses the various methods of acquiring usable samples for analysis by a number of explosives vapor and trace detectors or `sniffers', and describes a system under development at PSDB which, we believe, could enhance the performance of many of these systems.

A new method for real-time analysis of hazardous elements in sand and soils has been investigated. The method is based on laser plasma generation and time-resolved spectroscopy. Almost no sample preparation is needed and simultaneous multielemental analysis is possible. The data collection step takes only a few seconds, and the computer analysis and evaluation is carried out within minutes. The method has been tested for analysis of heavy metals in a variety of soil matrices. Good calibration plots have been obtained, with detection limits of ca. 10 ppm. An expert system has been developed for data analysis. The multivariate calibration model has been based on principle component regression technique in order to compensate for possible spectral interferences and some of the matrix effects.

A new detection system has been developed for real-time analysis of organic compounds in ambient air. It is based on multiphoton ionization by an unfocused laser beam in a single parallel-plate device. Thus, the ionization volume can be relatively large. The amount of laser created ions is determined quantitatively from the induced total voltage drop between the biased plates (Q equals (Delta) V(DOT)C). Mass information is obtained from computer analysis of the time-dependent signal. When a KrF laser (5 ev) is used, most of the organic compounds can be ionized in a two-photon process, but none of the standard components of atmospheric air are ionized by this process. Therefore, this instrument may be developed as a `sniffer' for organic materials. The method has been applied for benzene analysis in air. The detection limit is about 10 ppb. With a simple preconcentration technique the detection limit can be decreased to the sub-ppb range. Simple binary mixtures are also resolved.

Immunoassays (e.g., RIA, EIA) have been demonstrated to be useful for rapid, convenient detection and semiquantitative analysis of drugs. Thermedics Detection, Inc. manufactures a rapid, sensitive, self-contained, disposable, EIA device, developed by Bio-Metric Systems, Inc., designed to allow untrained personnel to perform in field situations. This format has been developed for drugs in biological fluids and on surfaces. The analyte in the test sample competes with an enzyme-analyte conjugate for a limited number of immobilized antibody sites. The AccuPRESS Test format can detect analytes at 10 ppb in biological fluids, water, and soil, and on surfaces, such as suitcases, vehicles, tables and hands, with positive results indicated by clearly visible color development within 5 minutes. This format is designed to have all dry components and to have an ambient shelf life of greater than one year. The format is available for cocaine and opiate derivatives, including heroin, and is readily adaptable for use with numerous other drugs, explosives, and environmental pollutants.

A Liquid Explosives Screening System capable of scanning unopened bottles for liquid explosives has been developed. The system can be operated to detect specific explosives directly, or to verify the labeled or bar-coded contents of the container. In this system nuclear magnetic resonance (NMR) is used to interrogate the liquid. NMR produces an extremely rich data set and many parameters of the NMR response can be determined simultaneously. As a result, multiple NMR signatures may be defined for any given set of liquids, and the signature complexity then selected according to the level of threat.

An antibody-based biosensor has been developed at the Naval Research Laboratory which is capable of detecting both drugs and explosives present at low levels in an aqueous sample. In the flow immunosensor, antibodies are immobilized onto a solid substrate, allowed to bind a fluorescently labeled signal molecule, placed in a small column and attached to a buffer flow. Upon sample introduction, an amount of the fluorescent signal molecule is released that is proportional to the concentration of applied sample. The response time of the sensor is under a minute, and multiple samples can be analyzed without the need for additional reagents. Quantitative assays are being developed for a variety of compounds, including TNT, DNT, PETN, and cocaine. The laboratory prototype has been used to study how choice of fluorophore, antibody density, and flow rate affect the signal intensity and column lifetime. A self-contained commercial instrument which can analyze up to seven different compounds from a single sample is currently being engineered under a Cooperative Research and Development Agreement.

A useful and important addition to characterization of identification of plastic explosives, especially ultra-low levels, by these analytical methods would be the ability to obtain their molecular weight or a pseudomolecular mass. This is difficult or impossible to do using conventional techniques since these compounds have low vapor pressures and are thermally labile. Using Fourier Transform--Ion Cyclotron Resonance--Mass Spectrometry, we have obtained molecular mass or pseudo-molecular mass information on some common explosives, viz. RDX, PETN and TNT.

This paper reports the results of a study using operant conditioning methods under laboratory conditions to determine the absolute threshold of dogs to an explosive compound. Testing was conducted in a behavioral laboratory setting consisting of a fully enclosed experimental chamber in which each dog worked, an olfactometer permitting the presentation of odors in precise concentrations expressed in terms of dilution of saturated vapor, and a computer that controlled all stimuli presented to the dog and recorded data. A series of daily sessions consisting of repeated trials of this procedure were conducted with 10 dogs. Throughout each session, the dilution of a saturated vapor in the air stream was systematically varied among dilutions above and below threshold, randomly alternating with clear air, until a threshold was determined. These procedures permitted the determination of absolute olfactory thresholds for a number of compounds. Data are reported regarding the variability of threshold performance across dogs for a single compound. Possible application of this testing technology to other questions are also discussed.

This paper describes an automated cargo inspection system (CIS) based on pulsed fast neutron analysis (PFNA). The system uses a pulsed beam of fast neutrons to interrogate the contents of small volume elements--voxels--of a cargo container or truck. The neutrons interact with the elemental contents of each voxel 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, explosives, and contraband. From the time of arrival of the gamma rays, the position of the voxel within the truck is determined. Full-scale physics simulation of time-dependent neutron and gamma ray interactions in various cargo materials have aided in the design of the system. These simulations have been benchmarked against laboratory measurements. A scaled model of the PFNA CIS is in operation in SAIC's PFNA facility and has been used to demonstrate the detection of drugs and other contraband concealed in a full-size cargo container with a variety of contents. A full-scale system is presently being designed and fabricated for the U.S. Government's Cargo Container Inspection Technology Testbed at Tacoma, Washington. This system is designed to scan five or more trucks per hour and is scheduled to come into operation in July 1995.

We have applied the Monte Carlo radiation transport code COG to assess the utility of a proposed explosives detection scheme based on neutron transmission. In this scheme a pulsed neutron beam is generated by an approximately seven MeV deuteron beam incident on a thick Be target. A scintillation detector operating in the current mode measures the neutrons transmitted through the object as a function of time. The flight time of unscattered neutrons from the source to the detector is simply related to the neutron energy. This information along with neutron cross-section excitation functions is used to infer the densities of H, C, N, and O in the volume sampled. The code we have chosen to use enables us to create very detailed and realistic models of the geometrical configuration of the system, the neutron source, and of the detector response. By calculating the signals that will be observed for several configurations and compositions of interrogated objects we can investigate and begin to understand how a system that could actually be fielded will perform. Using this modeling capability, many aspects of the design of a system can be optimized early on with substantial savings in time and cost and with improvements in performance. We will present our signal predictions for simple single element test cases and for explosive compositions. From these studies it is clear that the interpretation of the signals from such an explosives identification system will pose a substantial challenge.

We are modelling a number of the fast-neutron interrogation techniques currently under consideration, to include fast neutron transmission spectroscopy, pulsed fast neutron analysis, and its variant, 14-MeV associated particle imaging. The goals of this effort are to determine the component requirements for each technique, identify trade-offs that system performance standards impose upon those component requirements, and assess the relative advantages and disadvantages of the different approaches. In determining the component requirements, we will consider how they are driven by system performance standards, such as image resolution, scanning time, and statistical uncertainty. In considering the trade-offs between system components, we concentrate primarily on those which are common to all approaches, for example: source characteristics versus detector array requirements. We will then use the analysis to propose some figures of merit that enable performance comparisons between the various fast-neutron systems under consideration. The status of this ongoing effort is presented.

A relatively small and inexpensive neutron diagnostic probe system has been developed that can identify and image most elements having a larger atomic number than boron. It has the potential to satisfy van-mobile and fixed-portal requirements for nondestructive detection of contraband drugs, explosives, and nuclear and chemical warfare weapon materials, and for treaty verification of sealed munitions and remediation of radioactive waste.

During the 1980s the United States Federal Aviation Administration developed the thermal neutron analysis (TNA) automated explosive detection system for screening luggage taken aboard commercial air carriers. Six airport systems combining TNA and x-ray were built and deployed under a variety of conditions. This is an unclassified review of the deployment and the difficulties encountered when a system using a nuclear method to detect explosives is put into the field. The mechanical system, radiation safety, use of accelerators, system calibration, simulated explosives, types of luggage, and the test and evaluation procedures are reviewed.

Pure nuclear quadrupole resonance (NQR) of ¹⁴N nuclei is quite promising as a method for detecting explosives such as RDX and contraband narcotics such as cocaine and heroin in quantities of interest. Pure NQR is conducted without an external applied magnetic field, so potential concerns about damage to magnetically encoded data or exposure of personnel to large magnetic fields are not relevant. Because NQR frequencies of different compounds are quite distinct, we do not encounter false alarms from the NQR signals of other benign materials. We have constructed a proof-of-concept NQR explosives detector which interrogates a volume of 300 liters (10 ft³). With minimal modification to the existing explosives detector, we can detect operationally relevant quantities of (free base) cocaine within the 300-liter inspection volume in 6 seconds. We are presently extending this approach to the detection of heroin base and also examining ¹⁴N and ^35,37Cl pure NQR for detection of the hydrochloride forms of both materials. An adaptation of this NQR approach may be suitable for scanning personnel for externally carried contraband and explosives. We first outline the basics of the NQR approach, highlighting strengths and weaknesses, and then present representative results for RDX and cocaine detection. We also present a partial compendium of relevant NQR parameters measured for some materials of interest.

The LZH has carried out investigations in the field of rapid laser-supported material- identification systems for automatic material-sorting systems. The aim of this research is the fast identification of different sorts of plastics coming from recycled rubbish or electronic waste. Within a few milliseconds a spot on the sample which has to be identified is heated with a CO₂ laser. The different and specific chemical and physical material properties of the examined sample cause a different temperature distribution on the surface which is measured with an IR thermographic system. This `thermal impulse response' has to be analyzed by means of a computer system. The results of previous investigations have shown that material identification of different sorts of plastics can possibly be done at a frequency of 30 Hz. Due to economic efficiency, a high velocity identification process is necessary to sort huge waste currents.

A wide variety of nonintrusive inspection systems have been proposed in the past several years for the detection of hidden contraband in airline luggage and shipping containers. The majority of these proposed techniques depend on the interaction of radiation with matter to produce a signature specific to the contraband of interest, whether drugs or explosives. L-Division of the LLNL has developed a unique expertise in the combined numerical and experimental modeling of these types of systems. Based on our experience, we are convinced that detailed numerical modeling provides a much more accurate estimate of the actual performance of complex experiments than simple analytical modeling. Furthermore, the construction of detailed numerical prototypes allows experimenters to explore the entire region of parameter space available to them before committing their ideas to hardware. This sort of systematic analysis has often lead to improved experimental designs and reductions in fielding costs. L-Division has developed an extensive suite of computer codes to model proposed experiments and possible background interactions. These codes allow us to simulate complex radiation sources, model 3D system geometries with `real world' complexity, specify detailed elemental distributions, and predict the response of almost any type of detector. In this work, we will present several examples illustrating the use of these codes in modeling experimental systems at LLNL and discuss their potential usefulness in evaluating nonintrusive inspection systems.

Fluorescence spectra of final effluent samples from three sewage treatment plants show a remarkable similarity. For raw sewage samples, the fluorescence intensity is comparatively much higher than those of the final effluent and varies from sample to sample, although the spectral shapes are very similar. Fluorescence spectra of both raw sewage and final effluent samples, collected periodically over an eight-month period were recorded, and the UV- absorbance, pH, and conductivity of each sample were measured. The water Raman normalized fluorescence intensities of the samples from a particular plant at 350 nm emission wavelength are found to be correlated with the corresponding biochemical oxygen demand (BOD₅) values. When appropriate correction for chemical and environmental parameters are applied to the fluorescence data, the technique is considered to be suitable for real-time assessment of biodegradable carbon loading in sewage treatment plants for on-line process control.

Westinghouse Electric is developing portable, hand-held sensors capable of detecting numerous drugs of abuse (cocaine, heroin, amphetamines) and explosives (trinitrotoluene, pentaerythritol tetranitrate, nitroglycerin). The easy-to-use system consists of a reusable electronics module and disposable probes. The sensor illuminates and detects light transmitted through optical cells of the probe during an antibody-based latex agglutination reaction. Each probe contains all the necessary reagents to carry out a test in a single step. The probe has the ability to lift minute quantities of samples from a variety of surfaces and deliver the sample to a reaction region within the device. The sensor yields a qualitative answer in 30 to 45 seconds and is able to detect illicit substances at nanogram levels.

X-ray scattering at low angles demonstrates diffraction effects that can be used to characterize materials. The effects of overlying material are shown not to affect the usefulness of the data for the identification of explosives. The important features in the scattering signature are identified.

An investigation is being carried out into the potential use of elastic (or Rayleigh) scattered photons for the rapid identification of low atomic number materials. This technique has applications in the food industry for on-line quality control as well as areas such as security screening, materials recycling, and possible medical diagnostics.

Using the novel technique of energy-dispersive X-ray diffraction tomography, measurements were made of the coherent X-ray scatter from various types of foodstuff (chocolate, bacon, cherry jam, chicken breast) with their typical contaminants (macrolon, blue foil, cherry stones/wood and bone, respectively). In addition, it is shown how the use of a window technique in the diffraction spectrum allows cancellation of the foodstuff contribution in scatter images, leaving only that of the contaminant. The extension to multicomponent systems, allowing arbitrary elimination of unwanted materials in coherent scatter images, is possible. Taken together, these results indicate the great potential of coherent X-ray scatter analysis for contamination detection in the foodstuff industry. By development of more efficient X-ray scatter geometries, using e.g. fan beam irradiation with simultaneous acquisition of spectra from different voxels, the requirements of industrial mass production with respect to inspection time and resolution are likely to be met.

Bulk objects can be investigated for their material constituents by applying high-energy (30 keV to 100 keV) coherent X-ray scattering. When aiming at the detection of explosives in airport baggage, the technique allows discrimination between explosives and other substances. Coherent X-ray scatter measurements are presented for a set of explosives and their constituents as well as for a variety of nonexplosive materials. They demonstrate the superior material discrimination power of this method. The measurements have provided a quantitative basis for the prototype design of an airport baggage scanner. Sensitivity (200 g) and inspection time requirements (a few seconds) demand a highly application-specific system design with parallel acquisition and analysis of scatter spectra from different volume elements.

Material characterization based on the interaction of x and gamma radiation with matter is outlined and the need for a high intensity, monochromatic source highlighted. The design and properties of a new, fluorescent x-ray tube are described. This gives a high intensity (5.9 X 10⁹ photons s^-1 sr^-1 mm^-2), quasi- monochromatic output, consisting of the K fluorescent lines of its secondary target, a tantalum cone situated inside the tube. The spectral purity, stability and radiance are reported and comparisons made with radioisotope sources and a conventional tube monochromatized with a curved Ge crystal. In terms of radiance, the `Fluorex' x-ray set compares favorably with the former but not with the latter. However, it offers other advantages over these sources and without being fully optimized already has sufficient monochromatic output to find extensive use for material characterization.

The Schlumberger SYCOSCAN is a radioscopic control system designed to inspect freight containers and vehicles by X-rays. The X-ray detection is based on a modified version of a multiwire proportional chamber (MWPC) patented by Schlumberger. The MWPC principle was discovered by 1992 Physics Nobel Prize Winner G. Charpak. We present the detector's working principle. It presents simultaneously a high spatial resolution, a good detection efficiency, a high intrinsic gain and high dynamics. We will compare the SYCOSCAN detector to conventional scintillator/photodiode combinations.

X-ray diffraction tomographic imaging has been performed with laboratory and synchrotron- based instruments. Both instruments consist of beam-defining collimation slits, microcomputer-controlled specimen positioning stages, and multiple x-ray detectors that measure scattered and transmitted intensities as the specimen is moved through the primary pencil beam of radiation. This report describes the design of the instruments, and presents some preliminary results obtained with radiation of approximately 17 keV.

One-sided imaging techniques are currently being used in nondestructive evaluation of surfaces and shallow subsurface structures. In this work we present both analytical calculations and detailed Monte Carlo simulations aimed at assessing the capability of a proposed Compton backscattering imaging technique designed to detect and characterize voids located several centimeters below the surface of a solid.

This paper presents an overview of two recently constructed computed tomography (CT) scanners that have been designed to provide structural information for industrially relevant materials and components. CT enables cross-sectional slices of an object to be nondestructively imaged and represented as a map of linear attenuation coefficient. As linear attenuation is the product of mass attenuation and density, this usually enables a straightforward interpretation of the image in terms of density. The two instruments are a transportable scanner using a 160 kV(peak) powered x-ray tube for the inspection of wooden power poles up to 450 mm in diameter, and an industrial scanning system designed around an Ir-192 gamma-ray source for materials characterization and the testing and evaluation of castings, ceramics, and composites. The images presented in this paper have generally been reconstructed using the summation convolution back-projection (SCBP) method, and this technique is outlined. Direct Fourier reconstruction is also used and compared with the SCBP method. A brief discussion is offered on incorporating edge detection methods into the image reconstruction process for the improved identification of defects such as cracks and voids.

The key physical processes of a resonance-absorption-based explosive detection system (EDS) were individually computed modeled so that subsystem and total system performance could be simulated (i.e., a virtual prototype). Processes that were modeled included the radiofrequency quadrupole proton beam, resonant-energy gamma ray production by the reaction ¹³C(p,(gamma) )¹⁴N), gamma ray transport through inspected objects, individual detector response, output of a tomographic detector array, and tomographic image reconstruction. The simulations were used in designing individual subsystems of a laboratory EDS and in assessing their effect on overall system performance. The models were benchmarked to the actual performance of the prototype in developing performance requirements for an airport EDS. The several computer codes used in the simulation are described and the effectiveness of the overall simulation effort is discussed.

A prototype explosives detection system that was developed for experimental evaluation of a nuclear resonance absorption technique is described. The major subsystems are a proton accelerator and beam transport, high-temperature proton target, an airline-luggage tomographic inspection station, and an image-processing/detection-alarm subsystem. The detection system performance, based on a limited experimental test, is reported.

We describe a method for performing nuclear resonance absorption with the proton beam from a radio frequency quadrupole (RFQ) linear accelerator. The objective was to assess the suitability of the pulsed beam from an RFQ to image nitrogen relative to that of electrostatic accelerators. This choice of accelerator results in tradeoffs in performance and complexity, in return for the prospect of higher average current. In spite of a reduced resonance attenuation coefficient in nitrogen, we successfully produced 3D tomographic images of real explosives in luggage the first time the unoptimized system was operated. The results and assessments of our initial laboratory measurements are reported.

This work presents an exploration of several techniques for characterization of unknown multiple substances using interactions of fast neutrons with certain isotopic species. The techniques considered use these interactions to measure elemental densities to indicate the type of material being studied. Issues to be considered for practical application in security technology are spatial resolution, dilution effects, and size and cost limitations.

A prototype millimeter wave holographic surveillance system has been developed and demonstrated at the Pacific Northwest Laboratory (PNL). The prototype millimeter wave holographic surveillance system developed at PNL consists of a sequentially switched 2 X 64 element array coupled to a 35 GHz bi-static transceiver. The sequentially switched array of antennas can be used to obtain the holographic data at high speed by electronically sequencing the antennas along one dimension and performing a mechanical scan along the other dimension. A 1D mechanical scan can be performed in about one second. The prototype system scans an aperture of 0.75 by 2.05 m. This system has been demonstrated and images have been obtained on volunteers at Sea-Tac International airport in Seattle, Washington.

A wideband millimeter-wave imaging technique has been developed by the Pacific Northwest Laboratory (PNL) for the detection of concealed weapons carried by personnel through high- security areas, such as airports. A practical airport system based on this technique should be capable of real-time image frame rate of 10 to 30 frames per second. This technique, similar to an extremely high-resolution radar system, actively probes the target with millimeter-waves and reconstructs an image from the backscattered phase and amplitude data. The primary goal of the system is the detection of weapons and the placement of the detected weapon on the body. An important additional goal is the identification of detected items, which requires a high resolution imaging technique. An experimental system has been developed at PNL which has gathered millimeter wave imagery from clothed mannequins and human beings carrying concealed weapons. This system is capable of forming images in excess of 1 meter by 2 meters at resolutions on the order of 1 cm, and is capable of scanning in less than 5 seconds. This experimental system could be enhanced to function in real time by eliminating the relatively slow mechanical scan. A sequentially switched linear array of transceiver antennas would allow real-time gathering of the imaging information, since the data would be electronically scanned in the lateral direction and electronically swept in frequency. This allows formation of a 2D image from a 1D array of transceiver antennas.

An experiment involving the production and measurement of chemical vapors released from two volatile liquid solvents and a toxic gas was conducted on December 9, 1992 at a remote site near Sacramento, California. During this experiment, measured quantities of liquid diethyl ether and acetone and hydrogen chloride gas were released under controlled conditions inside a mobile-home-type structure. Vapor concentrations of the two solvents and the gas were measured both inside and outside the structure with a variety of techniques. Measurement equipment included a Bruel & Kjaer Type 1302 multi-gas monitor, Miran Foxboro 1BX portable ambient air analyzer, and Microtip photoionization detectors. Supporting meteorology data was also collected. Chemical vapor and meteorological measurements have been correlated and present a limited understanding of plume dynamics for this particular release scenario and difficult weather conditions. These experiments were carried out under high- humidity conditions just after heavy rain. The data has been plotted to show the concentration dispersion over the period of chemical vapor presence for the known release quantities and exhaust rates. Typical concentrations measured were less than 1 ppm for diethyl ether and HCL and from 0.5 to 5 ppm for acetone at a distance of ten to twenty meters from the release point. The results of this experiment provide a quantitative description of low-concentration hazardous chemical releases that can be used to validate chemical plume models as well as determine the necessity, viability, and sensitivity of remote-sensing detection concepts.

Results of a comparative study of the figure of merit (FOM) for various techniques for the detection of explosives and narcotics using neutrons as the interrogating radiation are presented. The calculations use the flux and energy of neutrons, the cross sections of nuclear reactions, the type and quantity of target material, the geometry of the detection system and the efficiency of the neutron and (gamma) ray detectors for arriving at the FOM of the detection systems based on neutron elastic scatter, associated particle imaging, pulsed fast neutron analysis, and pulsed fast-thermal neutron analysis.

This paper describes the image-quality performance specifications for X-ray scanners based on the operational requirements of the U.S. Customs Service. Technical specifications for resolution, contrast, and penetration are given for the detection of contraband in parcels, boxes, suitcases, crates, and cargo containers. Human factors issues as they relate to X-ray image interpretation are also discussed.

The physical principles of the nuclear resonance absorption method and its application to explosives detection are described. In this method, the object to be tested is scanned by a beam of 9.17 MeV gamma rays, which undergoes resonant attenuation whenever the beam encounters regions of nitrogen concentration. This resonant component of attenuation is detected using an array of gamma ray detectors containing a nitrogen-rich medium. From the reconstructed spatial distribution of nitrogen density obtained in multiview scanning, the presence of an explosive can be determined.

We describe a method of reconstructing the volume, and of estimating the lower bound of the density, of objects absorbing radiation by resonant (gamma-proton) reactions. The method is easily adapted to conical beams. The advantages of the imaging method to the detection of explosives in laboratory system based on nuclear resonance absorption are examined. The results of applying the method to the inspection of nitrogenous objects are presented, including the usefulness of oversampling and the relative success of differentiating explosives from innocuous materials based on nitrogen densities.

Superconducting quantum interference devices (SQUIDs) are the most sensitive detectors of magnetic fields yet devised. We have used a SQUID-based system to detect nuclear magnetic resonance (NMR) in several room-temperature samples. The results demonstrate that SQUID- detected NMR can be used to distinguish chemical differences between substances. The results also illustrate the broader potential of SQUID NMR for detecting specific materials in situations where conventional NMR is impractical.