WO1996013839A1 - Systeme d'inspection et technique de resolution spatiale pour la detection d'explosifs par interrogation neutronique et imagerie par rayons x - Google Patents

Systeme d'inspection et technique de resolution spatiale pour la detection d'explosifs par interrogation neutronique et imagerie par rayons x Download PDF

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Publication number
WO1996013839A1
WO1996013839A1 PCT/US1995/012631 US9512631W WO9613839A1 WO 1996013839 A1 WO1996013839 A1 WO 1996013839A1 US 9512631 W US9512631 W US 9512631W WO 9613839 A1 WO9613839 A1 WO 9613839A1
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Prior art keywords
neutron
density
information
set forth
inspection system
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PCT/US1995/012631
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English (en)
Inventor
Jeffrey W. Eberhard
Dan A. Gross
Robert J. Koss
Martin D. Rubin
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Lockheed Martin Specialty Components, Inc.
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Application filed by Lockheed Martin Specialty Components, Inc. filed Critical Lockheed Martin Specialty Components, Inc.
Priority to JP8514586A priority Critical patent/JPH10510621A/ja
Priority to EP95936230A priority patent/EP0792509A1/fr
Publication of WO1996013839A1 publication Critical patent/WO1996013839A1/fr
Priority to MXPA/A/1997/003225A priority patent/MXPA97003225A/xx

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
    • G01V5/20—Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
    • G01V5/22—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
    • G01V5/223—Mixed interrogation beams, e.g. using more than one type of radiation beam
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N23/00—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00
    • G01N23/02—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material
    • G01N23/04—Investigating or analysing materials by the use of wave or particle radiation, e.g. X-rays or neutrons, not covered by groups G01N3/00 – G01N17/00, G01N21/00 or G01N22/00 by transmitting the radiation through the material and forming images of the material
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
    • G01V5/20—Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
    • G01V5/22—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
    • G01V5/226—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays using tomography
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V5/00—Prospecting or detecting by the use of ionising radiation, e.g. of natural or induced radioactivity
    • G01V5/20—Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
    • G01V5/22—Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
    • G01V5/234—Measuring induced radiation, e.g. thermal neutron activation analysis

Definitions

  • the invention is directed to an inspection system and technique for the detection of explosives, for example, in luggage. More specifically, the invention is directed to an improved technique for the detection of explosives which uses a combination of neutron interrogation and X-ray imaging.
  • the detection technique must detect shaped moldable plastic explosives such as PETN and others which result in a partial volume fill even for small volumes.
  • Plastic explosives can be molded in combination with a camouflage material and can include shielding. Both the intrinsic explosive and the shielding should be identifiable independently. Because high explosives almost exclusively have a particularly separate chemistry in terms of oxygen and nitrogen content, chemical make-up constitutes a more certain signature than just density measurements based on X-ray inspection or measurement of hydrogen content (which is high for typical explosives) by means of NMR (nuclear magnetic resonance). NMR may experience problems with magnetic as well as conductive baggage contents and also does not provide a unique signature.
  • X-ray CT computed tomography
  • PET positron emission tomography
  • This technique provides an excellent signature analysis in that positron emission annihilation is detected by back-to-back synchronous monoenergetic photons of 511 keV.
  • the chemicals of interest, 15 O and 13 N are producible by photoproduction with energetic ⁇ rays, and have 2 and 10 minute half-lives, respectively. Difficulties arise, however, in generating a sufficiently intense source, low photoproduction cross sections, and a relatively expensive double detector array setup with very fast acquisition and processing times to handle ⁇ - ⁇ coincidences.
  • Neutron Interrogation (NI) ⁇ provides a variety of various techniques. It is possible to do attenuation and scattering measurements although this requires several distinct neutron incident energies in order to solve for all of the abundant chemical species (typically H, C, N, O, and others) in the explosive and other baggage materials. The multiple energy requirement makes this technique rather impractical.
  • Associated particle production from the reaction 3 H(d,n) 4 He using 14 MeV neutrons is a potentially feasible detection technique where the a particle is detected within the neutron generating source with good position resolution so as to provide a flight path of the neutron on the opposite side. While this technique provides very strong correlational information, individual events timing and a and n detection to within several nanoseconds must be accounted for, and therefore the system must account for a low rate of accidentals and background events. These considerations result in a reduced source production rate which in turn yields a low rate of excitation and/or activation events due to limited cross sections.
  • An object of the invention is to provide an improved apparatus and technique for detecting explosives.
  • X-ray CT computed tomography
  • neutron interrogation NI
  • X-ray CT computed tomography
  • NI neutron interrogation
  • X-ray CT is used to derive a physical density map of a bag.
  • the density map from X-ray CT and data from neutron interrogation is used to generate multi-dimensional (i.e., two or three dimensional) maps of the chemical make-up of the bag concents.
  • Information from the X-ray CT procedure is also used to focus the neutron interrogation on particularly suspect regions of interest in the bag.
  • an inspection system to inspect an object, such as luggage.
  • the inspection system includes a CT imaging system having an X-ray source and an X-ray detector array and a neutron interrogation system having neutron sources and a gamma detector array.
  • the inspection system also includes a processor which is connected to the CT imaging system and to the neutron interrogation system.
  • the processor includes a density computation module to generate a multi-dimensional density map of the object based on data from the CT imaging system and a chemical species computation module to generate a multi-dimensional map which indicates the concentration of at least three elements (e.g., nitrogen, carbon and oxygen) in the object based on information from the neutron interrogation system and on density information from the density computation module.
  • the processor also includes a localization module to provide region-of-interest information for neutron interrogation based on information from the density computation module.
  • Information from the localization module can be used to focus neutron interrogation on high density areas within the object.
  • carbon measurements can be used for normalization of nitrogen and oxygen measurements to eliminate systematic errors common to carbon, nitrogen, and oxygen measurements.
  • a method of detecting explosives in an object includes irradiating the object with X-rays and measuring the attenuation and scattering of the X-rays in the object. Information representing the density make-up of the object is generated based on this attenuation and scattering information.
  • the object is also irradiated with neutrons and the number and energy of gamma particles resulting from neutron-gamma reactions (abbreviated "(n, ⁇ )") in the object are measured.
  • Information regarding the presence or absence of explosives in the object is then generated based on the measurement of the gamma particles and on the density information.
  • the neutron interrogation can be focussed on high density areas within the object based on the density information.
  • Figure 1 illustrates an inspection system according to a preferred embodiment of the invention
  • Figure 2 illustrates an X-ray CT imaging system which is suitable for use in the inspection system of Figure 1;
  • Figures 3 and 4 illustrate the operation of the X-ray CT imaging system of Figure 2;
  • Figure 5 illustrates a neutron interrogation system which is suitable for use in the inspection system of Figure 1;
  • Figure 6 illustrates a portion of the BGO (bismuth germinate) pulse processing circuitry of Figure 5;
  • FIG. 7 is a flowchart which illustrates a specific application example of the present invention.
  • the present invention combines functions of X-ray CT and neutron interrogation (NI).
  • X-ray CT is used to derive a physical density map of an object such as a bag and NI is used to determine the chemical composition of regions within the object.
  • the NI procedure uses the density map from X-ray CT to generate and better resolve multi-dimensional maps, such as three dimensional maps, showing the chemical make-up of the bag contents.
  • Information from the X-ray CT procedure is also used to focus the neutron interrogation on particularly suspect regions of interest.
  • information from the X-ray CT procedure is used to employ a large number of small pixels to interrogate high density areas (which are the most likely to contain explosives) and to employ only a small number of large pixels to interrogate low density areas (which are the least likely to contain explosives).
  • focussed pixelation we call this use of the X-ray CT information "focussed pixelation.”
  • NI can extract both the ratio and relative values of the oxygen and nitrogen molar densities. Elimination of the "relative" term requires a normalization factor.
  • CT is used to measure the physical density of the object and is thus used to provide a normalization factor and bounding constraint for NI.
  • the chemical composition of the explosive offers an intrinsically useful and abundant species, such as carbon
  • its relative density can be used for another type of normalization.
  • This later technique has the advantage that carbon is measured in conjunction with oxygen and nitrogen and therefore has very similar systematic measurement error distortions.
  • carbon is also the most abundant species with the largest (n, ⁇ ) cross section among ordinary typical baggage contents.
  • the concentration of carbon is about the same for non-explosives (such as clothes) and explosives. Accordingly, use of carbon measurements for normalization of the nitrogen and oxygen measurements eliminates errors that are common to the carbon, nitrogen, and oxygen measurements.
  • the invention employs optimal modeling of neutron source, baggage and detector coupling in a physical embodiment and optimal algorithmic extraction of detector data relating to explosives identification.
  • the primary steps of the technique are that highly localized oxygen and nitrogen density distribution maps are generated for a typical airline bag to provide respective visual images, to compute threshold triggers for the signature of high explosives and to satisfy overall density consistency checks indicative of explosives in locations which are designated as suspect.
  • the detection process develops a large SNR (signal-to-noise ratio) on a statistical basis in order to ensure a low rate of false negative non-triggers and simultaneously ensure a low rate of false positive triggers so as not to burden the throughput process with redundancy checks and unnecessary manual inspection.
  • the inspection system has a minimum number of moving parts to ensure low phonic detector noise and operational reliability.
  • the system is also minimally invasive in the activation sense in that it makes optimal use of the bag geometry and illuminates the bag using a tightly coupled neutron source and a tightly coupled detector array. This tight coupling enhances the event rate which conversely entails a reduced exposure time requirement.
  • the information from the CT procedure is highly reliable and accurate and is thus also used to constrain and check the somewhat less resolved results from NI. This combination attains a much better performance as compared with either CT or NI by itself.
  • FIG. 1 illustrates an inspection system 1000 according to the invention.
  • the inspection system 1000 inspects a bag B using a CT imaging system and a neutron interrogation system.
  • the CT imaging system includes an X-ray source 1110 and an X-ray detector array 1120.
  • the neutron interrogation system includes neutron sources 1010 and a gamma detector array 1020. Both the X-ray detector array 1120 and the gamma detector array 1020 are connected to a processor 500, which includes array pulse processing modules/circuitry 512 and 513.
  • the processor 500 is in turn connected to a display 400, which provides information to a system operator.
  • the system operator controls the inspection system via an input device 402.
  • the bag B is passed through the CT imaging system and the neutron interrogation system. As the bag passes between the X-ray source 1110 and the X-ray detector array 1120, X-rays pass through the bag and the X-rays transmitted through the bag are detected by the detector array 1120.
  • the bag After the bag is inspected by the CT imaging system, the bag passes in between the neutron sources 1010 and the gamma detector array 1020.
  • the neutron sources emit neutrons into the bag which react with material inside the bag.
  • These neutron-gamma reactions (abbreviated "(n, ⁇ )”) generate gamma (“ ⁇ ") rays which are detected by the gamma detector array 1020.
  • the X-ray detector array 1120 provides information to the processor 500 which is used by the processor 500 to create a three-dimensional density map of the bag, using CT density computation module 510.
  • the gamma detector array 1020 stores information regarding the number and energy of gamma rays received by the gamma detector array. This information, may be stored, for example, in histograms.
  • the information from the gamma detector array 1020 is used by the processor 500 to compute a three-dimensional map which shows the concentration of nitrogen, carbon, and oxygen in each pixel, or voxel, in the bag, using an N, C, and O chemical species computation module 520.
  • the computation module 520 uses density information from the density computation module 510, as will be described in further detail below.
  • information from the density computation module 510 is used by an NI localization module 530 to provide region-of-interest ("ROI") information to the gamma detector array 1020 and to the computation module 520.
  • ROI information indicates, for example, which portions of the bag have very low densities and which portions of the bag have high densities.
  • the computation module 520 uses the information from the localization module 530 to focus on the high density areas. For example, a large number of small pixels is employed to interrogate high density areas (which are the most likely to contain explosives) and only a small number of large pixels is employed to interrogate low density areas (which are the least likely to contain explosives).
  • CT based information from the CT density computation module 510 and NI based information from the chemical species computation module 520 is provided to a CT and NI image fusion module 540 which fuses the CT based and NI based information together and generates a threedimensional map accurately showing the concentration of each of the three elements nitrogen, carbon, and oxygen in each pixel of the bag. This map is displayed on the display 400 along with other information.
  • a scale 300 in order to weigh the bag.
  • the scale 300 is coupled to the processor 500 via a signal line 301.
  • the weight of the bag can be determined either physically by such a scale or algorithmically from information provided by the CT imaging system. Weight information based on physically weighing the bag is very accurate and can therefore be used, if necessary, to constrain results derived from calculations.
  • the system 1000 may also optionally include a mechanical assembly to reorient the bag as it passes from the CT imaging system to the neutron interrogation system based on the ROI information.
  • the NI system needs density information from CT, primarily in the yz plane, with less accent in the x coordinate direction of the bag to be pixelated.
  • a full purpose CT system would certainly suffice in an algorithmic, pixel and density resolutions sense.
  • the density and spatial resolution requirements for baggage inspection are not as demanding as, for instance, medical use CT. Therefore, a special purpose and much more practical and cost effective CT system is used in the present invention.
  • the features are a much reduced spatial and density resolution while at the same time a total throughput of the scanned volume of about 15 liters/sec, for an average exposure of 5-6 seconds per bag, commensurate with a typical baggage size and transit rate.
  • FIGS. 2 to 4 will be used to describe one suitable CT X-ray imaging system.
  • Another suitable imaging system is described in the United States Patent Application which was filed on October 20, 1994 by Jeffrey W. Eberhard and Meng-Ling Hsiao and entitled "X-Ray Computed Tomography (CT) System for Detecting Thin Objects," the entire contents of which are incorporated herein by reference.
  • CT Computed Tomography
  • stationary BGO detectors 120 and an X-ray source 110 inspect baggage while the baggage slowly drifts past on a conveyor belt (not shown) .
  • a mechanical switch (not shown) or other sensor indicates when the bag is properly positioned between detectors 120 and X-ray source 110.
  • Figure 2 shows a 6 ⁇ 7 detector array.
  • detector array 120 consists of a 27 ⁇ 36 array.
  • a limited view solid angle X-ray fan beam with a two-dimensional aperture scans the bag with X-rays tracking into two-dimensional detector 120 on the far side of the bag.
  • the X-ray beam is mainly in the z direction with opening angles of more than 30° in the width direction (x) and 40° in the transit direction (y) .
  • the detector 120 has 1/2" ⁇ 1/2" square BGO crystals over an aperture of 13.5" ⁇ 18", to form 972 detector channels.
  • the detectors are connected to BGO pulse processing circuitry 130.
  • the detectors constantly digitize the flux rate of event energies above a certain threshold.
  • the individual channel circuitry employed is similar to that used in conventional CT systems.
  • the circuitry produces a detector frame or state of all 972 channels every 50 msec.
  • this strip is primarily selecting a vertical slice of the bag relative to a point source, with somewhat converging lateral surfaces.
  • Using 36 detectors with about 120 oriented attenuation/scattering integrals provides a deconvolution of the slice and consequent density extraction.
  • a similar procedure is followed for each y oriented detector strip. The total output of all deconvolution results in a three-dimensional pixelation of the bag into about 100,000 pixels with better than a 1/2" ⁇ 1/2" ⁇ 1/4" size.
  • This limited viewing angle CT system is immobile, provides complementary data for the downstream NI inspection in precisely the required pixelation, has sufficient two- and three-dimensional resolution, and is much faster than a standard CT approach due to the limited resolution requirements.
  • Figures 3 and 4 illustrate the operation of the X-ray imaging system of Figure 2.
  • the bag B passes in between source 110 and detector array 120.
  • Figure 3 illustrates the X-ray paths at five different positions.
  • Figure 4 illustrates the superposition of the X-ray paths at the five positions of Figure 3.
  • the information from the superposition of X-rays is used to create a map w(y,z) indicative of the density of the bag contents.
  • Figure 4 illustrates a two-dimensional density map, in practice, a three-dimensional density map is generated.
  • the map w(y,z) is then normalized, using, for example, the weight of the bag.
  • the number of pixels used for the CT process is generally much, much greater than the number of pixels used for NI.
  • FIG. 5 shows a typical 8" ⁇ 20" ⁇ 30" bag B passing between tightly geometrically coupled neutron sources (NS) 10-1 to 10-7 and BGO detectors 20-1,1 to 20-14,8. For clarity, Figure 5 shows only 7 neutron sources and 112 detectors. In practice, 10 neutron sources are provided and 600 1" ⁇ 1" detectors are provided in a 20 x 30 array.
  • NS tightly geometrically coupled neutron sources
  • the neutron sources are formed as an array of individual zetatrons and are operated by electrical sequencing in the z direction and mechanical scanning along the y direction.
  • the neutron sources are surrounded by moderator material, typically rich in hydrogen, such as polyethylene or paraffin, with some additional deuterated polyethylene to enhance the scattering cross section at high-energy reactions.
  • moderator material typically rich in hydrogen, such as polyethylene or paraffin, with some additional deuterated polyethylene to enhance the scattering cross section at high-energy reactions.
  • a thin lead liner (not shown) is used immediately around each zetatron as an effective neutron multiplier above 10 MeV due to a large number of (n,2n) reactions.
  • Lead is safe as a low (n, ⁇ ) cross section choice and has a relatively high ⁇ nel with favorable kinematics to essentially reflect neutrons due to the heavy nucleus of lead, thus providing a relatively enhanced low-energy density, such as in a containment.
  • This is also a blanket of a much larger radius than the inner liner, for example, 10-15 cm in radius, which is terminated with lead and acts to produce, by repeated collisions of neutrons with hydrogen, thermal neutrons whose diffusion in the bag gives rise to the (n, ⁇ ) signature reactions for nitrogen as shown below:
  • detection of 10.8 MeV and 5.1 MeV ⁇ 's indicates nitrogen; detection of 4.4 MeV ⁇ 's indicates carbon; and detection of 6.1 MeV ⁇ 's indicates oxygen.
  • the BGO detector array 20 is pixelated to a maximum feasible level in terms of both cost and physics simplicity. No multiple pixels are provided for summing ⁇ energy because this would introduce a vast layer of data handling software (for example, for pattern recognition and fast timing of coincidences) required to operate at well above 1 MHz incoming events. Multipixel shared energy considerations is not, however, precluded by the DSEX and GSO model to be described below, if desired in a particular application.
  • a single BGO channel's event processing electronics is shown in Figure 6.
  • the event processing time is about 1 ⁇ sec due to the BGO time constant of 300 nsec.
  • the CT system is used to pre-scan the bag prior to NI.
  • the CT system provides density information and can be used to normalize the total bag weight.
  • the CT system provides enough intelligence to allow the NI to form a scan and bag pixelation strategy and, if desired, determine the optimal orientation of the bag.
  • the bag is stationary for a residence time between the gamma detector array and the neutron sources.
  • the optimal GSO (to be described below) couplings are enforced and the geometry is not varied to maintain low real time computational loads for the GSOs and to keep systematic errors and their variability to a low level. Some systematic errors due to histogrammed background or peripheral incoherent reactions cause a count rate sensitivity.
  • the NI data rates and statistical errors are extracted for pulse on and off phases from separate histograms and are passed to a DSEX solver/inverter (to be described below) which employs bag densities and a covariance matrix.
  • This data is presented in terms of contour plots of ratios of species, normalized by the CT information, and consistency checks for partial pixel analysis for CT, and the main CT physical density distribution is expressed in contour maps.
  • the zetatron neutron sources are operated at a 10% duty factor and are tightly coupled geometrically to the baggage.
  • the source flux is isotropic and yields 14 MeV monoenergetic neutrons from d+t reactions.
  • Signals from the pixelated wall of BGO scintillation detectors are used in conjunction with individual channel pulse processing and pulse height analysis to create histograms of the secondary flux distribution due to prompt and delayed (n, ⁇ ) reactions.
  • the ⁇ spectra are accumulated in separate histograms for the source on and off phases for reasons of background differentiation.
  • Each of the species carbon, oxygen and nitrogen has a ⁇ energy signature with an associated energy resolution. The energy resolution is dominated by the BGO detector total energy capture efficiency, but the energy resolution is also a function of Compton scattering between the reaction position in the baggage and the detector location due to intervening material.
  • the moment (s) of inertia (i.e., lopsidedness) of the bag can be determined prior to CT imaging to provide additional information to identify suspect regions.
  • a first Monte Carlo analysis generates a neutron fluence for both fast and thermal neutrons at each location in the baggage.
  • the effects included in this first Monte Carlo calculation are:
  • reaction rate and attenuation and scattering based on a real time model of atomic densities derived from a prior CT procedure.
  • the output of this first Monte Carlo analysis is compactly represented by a coupling matrix relating NS positions and bag-pixels and is addressed in the form of a generalized source-to-bag solid angle, ⁇ sb .
  • a second Monte Carlo analysis relates each bag-pixel to each detector pixel, at a standard fluence, accounting for:
  • the output of the second Monte Carlo analysis is compactly represented by a coupling matrix relating bag-pixels and detector pixels and is addressed in the form of a generalized bag-to-detector solid angle, ⁇ M .
  • GSOs Generalized solid angle matrices
  • the preceding description relates to fluences (n/cm 2 ) and ( ⁇ /cm 2 ).
  • the detector observations are based on flux (fluence per unit time).
  • a separate integrating detector channel measuring the neutron flux directly based on, for example, *He for thermal neutrons and (n, ⁇ ) for fast neutrons is used as a continuous flux calibration standard based on a standard geometry and yields the NS neutron current.
  • the main BGO integrated detectors are calibrated periodically using phantoms.
  • N d is ⁇ generic fluence expression for a thin target, where N d , ⁇ , p , and L are the observed reaction rate per unit input rate, the reaction partial cross section, the target density and the target thickness, respectively.
  • the second equation expresses the relationship between neutrons from the neutron sources, a particular pixel, and the gammas detected by the gamma detector array.
  • the first term is a vector
  • the second term ⁇ sb is a matrix which represents the solid angle between a particular neutron source and a particular pixel (plus additional attenuation and scattering effects indicated above).
  • the third term ⁇ (n, ⁇ ) is the cross section of one of the three elements (carbon, nitrogen, or oxygen) of interest.
  • the fourth term ⁇ is a vector representing the density within a pixel and the fifth term ⁇ L bag-pixel > n represents the integrated path length of a particular pixel.
  • the sixth term is a matrix which represents
  • the seventh term f BGO represents the efficiency of the detector elements.
  • the term on the right-hand side is a vector which represents the gammas received at the detector array for each specific source position.
  • the equation for R ds which is really three or more equations relating to each detectable species, is a more accurate representation than the first equation because it relates to a thick target in which reactions are treated on a bag-pixel by bag-pixel basis, with each bag-pixel being relatively equivalent to the simple fluence equation.
  • the (n, ⁇ ) cross section ⁇ (n, ⁇ ) is moderated by the GSO ⁇ sb .
  • the bag-pixel density and transit length ⁇ b and ⁇ L bag- pixel >, respectively, are expressed more specifically in terms of species density, per specific pixel, and are represented as an integral of neutron track length per transverse geometrical cross section, N ⁇ L/V>.
  • the remaining factors to be considered are the NS rate ds n /dt, the detector observation rate R ⁇ and the BGO efficiency for ⁇ energy collection, f BGO .
  • the second equation is in a matrix form. There are several quantities which are considered sealers: the ⁇ (n, ⁇ ) partial cross sections and the detector efficiency at the proper species energy, f BGO .
  • Both the bag and the detector are pixelated, the former algorithmically and the latter physically by discrete detectors.
  • Two arrays of all respective bag and detector locations form the density times pixel thickness and detection rate and are vectors.
  • the NS is allowed to move to various inspection locations so its rate is a vector although the actual entries are all equal to the NS neutrons/second rate.
  • the remaining matrix quantities, the GSOs, relate phase spaces of the NS to the bag and the bag to the detectors. Both matrices encompass geometric solid angles, attenuation, scattering, and the like, for the respective beam-target process.
  • the flux equation can be rearranged to represent more closely its ultimate utilization. Reinterpreting the variables we have: We call this equation the density solution equation (DSE). The relations to the flux equations are:
  • the denominator in this equation is a normalization current for reactions that eventually terminate in the properly detected species, promptly or as half-life decays. It is apparent that the above equations have a relationship to a detector integrating time interval and the time interval's phasing with respect to the NS time domain modulation.
  • ⁇ bd Data is collected in separate histograms for the NS on and off times because background events and dead times are expected to be different. This is not shown specifically but is lumped into the character of ⁇ bd .
  • the ⁇ bd matrix in the DSE relates the number of detector channels, that is, detector pixels, to the algorithmic bag-pixels. A solution exists only if the dimension of the R ds vector is larger than the dimension of the bag-pixels vector.
  • NS for neutron source(s) is used in a broad sense to encompass the detailed physics of the intrinsic zetatron NS and the construction of the neutron thermalization blanket.
  • the zetatron quasi point source becomes more extended in the context of thermal neutrons.
  • Time domain aspects of the DSE account for a slow activation process from exposure start and thermal neutron transients relating to zetatron on and off pulse structure. These time domain features are reflected in the GSOs.
  • the limited zetatron neutron current may be partially bypassed for long-lived states equal to or longer than the bag residence time near the detector, such as oxygen channel events, by exposure prior to insertion of the bag into the neutron interrogation enclosure.
  • the curly brackets represent the respective one-dimensional and two-dimensional quantities properly weighted to account for the detection statistical errors, ⁇ R ds .
  • Standard theory leads to a solution for the covariance matrix. This matrix then makes available the self and correlation errors relating bag-pixels.
  • the upshot is a bag density with calculated errors in terms of standard deviations, i.e., a signal-to-noise ratio. This relates intimately to the number of both false positives and false negatives at the explosive detection level.
  • the GSOs ⁇ sb and ⁇ bd as well as ⁇ L> n employed in the neutron interrogation data processing procedure described above require knowledge of the densities in the bag.
  • CT system precedes the NI process and provides the required physical density information.
  • a statistical model or equivalent is used to associate a species density to bag-pixels in order to calculate the GSO matrices.
  • the bag density final solution for each species can be iterated in calculating the GSOs. Since the GSOs depend primarily on the solid angle, it is proper to inject an initial estimation of the species densities, which for initial estimation purposes can be considered uniform throughout the bag as long as numerical convergence is guaranteed for the iterative process of recirculating interim density solutions. This is equivalent to a situation in which the structure of the bag is a relatively small perturbation on the GSO's computation, through attenuation and scattering, and the like.
  • NI does not necessarily cover the signature of all feasible atomic species in baggage.
  • practical considerations relating to BGO detectors or any other type of detector place a limit on the maximum number of physical channels per NI system. These considerations include the total energy collection per individual crystal, i.e., the number of radiation lengths for the crystal. Shared crystal events with partial energy in two or more crystals are not considered a viable solution in this context due to high cost and increased system complexity, but are totally compatible with the underlying model developed for NI and reflected in the DSEX model. This then provides an upper threshold for bag pixelation in the final density solution.
  • An additional function of CT is to enable the normalization of the bag-pixel using a physical density which relates in part to C, N and O.
  • the vast majority of all significant content species are represented by C, N and O.
  • the NI pixels for a typical bag are rather large, therefore a combination of high-density explosive in a small amount and a low-density material (say wool) in a large amount, volumetrically, or either extreme of materials choices, cannot be discriminated on the NI basis alone.
  • a subdivision of NI pixels using CT identifies subpixel regions falling within a range density for explosives. It is not enough, however, to identify regions having a density range corresponding to explosives, the proper oxygen and nitrogen densities must be verified. This is accomplished by a consistency check as follows.
  • the consistency check subtracts all of the volume of the suspect density as if it were explosive and finds the remainder pixel volume complement O and N densities. Since O and N are high density for explosives, a false explosive association (false positive) with a high density will cause the remainder to have a negative oxygen and nitrogen density for the pixel volume complement, that is, a false premise of explosive in the subpixel region of the suspect density.
  • a further resolving method is obtained by repixelation of the bag to segregate non-suspicious regions in terms of density to a few in number while dividing the remainder of the bag volume into smaller than average pixel sizes.
  • This CT data biased pixelation is advantageous and is perfectly admissible into the DSEX model. By doing so, the suspect pixel statistics improves and subsequently the consistency checks (using the O/C and N/C ratios and the budget-remainder method described above) obtain a better SNR. Whereas a uniform pixelation would allow only two-dimensional bag-pixels due to the limiting number of detector channels.
  • a focused pixelation based on a CT focused region allows even a local three-dimensional pixel structure with sparse pixelation elsewhere.
  • FIG. 7 is a flowchart which illustrates a specific application example of the present invention.
  • step S1 the bag is weighed.
  • step S2 moment(s) of inertia (i.e., lopsidedness) of the bag are determined by physical measurement. Other low and high order mass moments with respect to multiple axes can also be determined, if necessary.
  • CT imaging is used to derive a density for each pixel, or voxel, with high resolution using uniform local exposure.
  • the CT density information is normalized based on weight and moment information from steps S1 and S2 on a per bag basis. In certain applications it may be necessary or desirable to perform multiple CT passes.
  • step S4 the pixelation for NI is determined. Small pixels, resulting in high resolution, are selected for regions of interest identified by the CT imaging and larger pixels are used elsewhere.
  • step S5 neutron interrogation (NI) is performed and histograms of the resulting gamma energies are created. The spectral contributions for carbon, nitrogen, and oxygen (and any other spectrum distinct species of interest such as hydrogen) are ascertained in step S6, and compensation is made for background events.
  • step S7 neutron attenuation and scattering in intervening material prior to reaction in each bag pixel is calculated.
  • step S8 the neutron-to-target species interaction for neutron reactions and neutron-to-gamma conversion is calculated for each pixel by means of solid angle, attenuation, scattering, and the like.
  • Step S9 computes the number of gammas emitted from each pixel and their attenuation and scattering in intervening material prior to reaching the gamma detectors. Compensation is made for detector registration, detector inefficiencies, detector geometrical losses, and detector reaction-based losses in step S10.
  • step Sll an initial pass to determine the carbon, nitrogen, and oxygen localization in each pixel is performed using the inversion process described above.
  • step S12 numerical constraints are applied to the initial pass from step S11. These constraints include positive density bounds for each pixel for each chemical species separately and constraints for total carbon, nitrogen, and oxygen (plus any other species of interest) with respect to the maximum CT derived physical densities for each pixel.
  • Step S13 determines if prescribed convergence criteria are satisfied. If not, new attenuation and scattering coefficients are calculated in step S7 and the process is iterated, or repeated. Portions of steps S4 to S6 may also be updated or reperformed. Once the prescribed convergence criteria are satisfied, the CT based and NI based information is used to generate a three-dimensional map accurately showing the concentration of each of the three elements nitrogen, carbon, and oxygen (and possibly hydrogen and others) in each pixel of the bag in step S14. This map is displayed on the display along with other information.
  • X-ray CT systeme may be used instead of the X-ray CT system shown in Figure 2.
  • density information can be provided by a non-CT X-ray system or density information for NI can be based on physical measurements of weight and/or moments of inertia or on approximations based on the make-up of typical bags and stored in a memory.
  • NI can be conducted using single or multiple neutron sources.
  • NI image construction can be based on the spatial configuration of neutron sources or on electronically scanning the neutron sources, or both.

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Abstract

La tomodensitométrie et l'interrogation neutronique sont combinées pour former un système d'inspection (1000) et une technique de résolution spatiale pour la détection d'explosifs. La tomodensitométrie (510) est utilisée pour dériver une carte de densité physique d'un sac (B). Cette carte de densité obtenue à partir de la tomodensitométrie (510) et de l'interrogation neutronique sert à produire des cartes en trois dimensions de la constitution chimique du contenu du sac (B). Les informations obtenues à partir de la procédure de tomodensitométrie servent également à concentrer l'interrogation neutronique sur des zones particulièrement suspectes du sac (B)
PCT/US1995/012631 1994-10-31 1995-10-23 Systeme d'inspection et technique de resolution spatiale pour la detection d'explosifs par interrogation neutronique et imagerie par rayons x WO1996013839A1 (fr)

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JP8514586A JPH10510621A (ja) 1994-10-31 1995-10-23 中性子問合せ及びｘ線撮像の組合せを用いた、爆発物を検出するための検査システム及び空間解像技術
EP95936230A EP0792509A1 (fr) 1994-10-31 1995-10-23 Systeme d'inspection et technique de resolution spatiale pour la detection d'explosifs par interrogation neutronique et imagerie par rayons x
MXPA/A/1997/003225A MXPA97003225A (en) 1994-10-31 1997-04-30 Space resolution inspection and technique system for detecting explosives using neutrones interrogation and x-ray image formation, combine

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EP0852717A1 (fr) * 1995-09-26 1998-07-15 Vivid Technologies, Inc. Detection de contrebande au moyen d'un procede de tomographie interactive utilisant des sondes multiples
WO1999049311A2 (fr) * 1998-02-18 1999-09-30 Hienergy Microdevices, Inc. Procede et dispositif permettant de detecter, de localiser et d'analyser des composes chimiques par activation de particules subatomiques
WO2000025268A2 (fr) * 1998-10-26 2000-05-04 Romidot, Ltd. Tomographie assistee par ordinateur pour inspection non destructive
WO2000043760A2 (fr) * 1999-01-20 2000-07-27 Heimann Systems (Societe Anonyme) Systeme de discrimination de matieres organiques et inorganiques
WO2004090576A2 (fr) * 2003-04-02 2004-10-21 Reveal Imaging Technologies, Inc. Systeme et procede de resolution des menaces dans la detection automatisee des explosifs a l'interieur des bagages et autres colis
US6928131B2 (en) * 2001-11-08 2005-08-09 Ratec, Ltd. Method for detecting an explosive in an object under investigation
WO2006012703A1 (fr) * 2004-08-06 2006-02-09 Commonwealth Scientific And Industrial Research Organisation Systeme et procede d'affichage de donnees
US7046761B2 (en) 2003-01-23 2006-05-16 Reveal Imaging Technologies, Inc. System and method for CT scanning of baggage
US7103137B2 (en) 2002-07-24 2006-09-05 Varian Medical Systems Technology, Inc. Radiation scanning of objects for contraband
US7123681B2 (en) 2002-10-02 2006-10-17 L-3 Communications Security And Detection Systems, Inc. Folded array CT baggage scanner
US7162005B2 (en) 2002-07-19 2007-01-09 Varian Medical Systems Technologies, Inc. Radiation sources and compact radiation scanning systems
US7224765B2 (en) 2002-10-02 2007-05-29 Reveal Imaging Technologies, Inc. Computed tomography system
WO2007130857A2 (fr) * 2006-05-05 2007-11-15 American Science And Engineering, Inc. Tomodensitométrie combinée à rayons x/système d'identification à neutrons
US7313221B2 (en) 2002-12-10 2007-12-25 Commonwealth Scientific And Industrial Research Organization Radiographic equipment
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US7440544B2 (en) 2004-02-11 2008-10-21 Reveal Imaging Technologies, Inc. Contraband detection systems and methods
US7440537B2 (en) 2003-10-02 2008-10-21 Reveal Imaging Technologies, Inc. Folded array CT baggage scanner
US7663119B2 (en) 2004-08-12 2010-02-16 John Sved Process for neutron interrogation of objects in relative motion or of large extent
CN1723388B (zh) * 2002-12-10 2011-01-26 联邦科学和工业研究委员会 射线照相设备
CN102279141A (zh) * 2010-06-12 2011-12-14 中国民航科学技术研究院 用于检测ct型安全检查设备的测试箱
EP2259092A3 (fr) * 2009-06-02 2012-03-28 Applied Signal Technology Inc. Système d'inspection pour déterminer la composition du contenu d'un article
US9746583B2 (en) 2014-08-27 2017-08-29 General Electric Company Gas well integrity inspection system
WO2023065671A1 (fr) * 2021-10-18 2023-04-27 同方威视技术股份有限公司 Système et procédé de détection entièrement automatique
WO2024064896A1 (fr) * 2022-09-22 2024-03-28 Analogic Corporation Détermination de propriétés physiques d'éléments introduits dans un système de balayage à rayons x, et systèmes, procédés et appareils associés

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Cited By (43)

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Publication number Priority date Publication date Assignee Title
EP0852717A1 (fr) * 1995-09-26 1998-07-15 Vivid Technologies, Inc. Detection de contrebande au moyen d'un procede de tomographie interactive utilisant des sondes multiples
EP0852717A4 (fr) * 1995-09-26 1999-08-18 Vivid Tech Inc Detection de contrebande au moyen d'un procede de tomographie interactive utilisant des sondes multiples
WO1999049311A2 (fr) * 1998-02-18 1999-09-30 Hienergy Microdevices, Inc. Procede et dispositif permettant de detecter, de localiser et d'analyser des composes chimiques par activation de particules subatomiques
WO1999049311A3 (fr) * 1998-02-18 2000-01-20 Hienergy Microdevices Inc Procede et dispositif permettant de detecter, de localiser et d'analyser des composes chimiques par activation de particules subatomiques
WO2000025268A2 (fr) * 1998-10-26 2000-05-04 Romidot, Ltd. Tomographie assistee par ordinateur pour inspection non destructive
WO2000025268A3 (fr) * 1998-10-26 2000-07-20 Romidot Ltd Tomographie assistee par ordinateur pour inspection non destructive
WO2000043760A2 (fr) * 1999-01-20 2000-07-27 Heimann Systems (Societe Anonyme) Systeme de discrimination de matieres organiques et inorganiques
WO2000043760A3 (fr) * 1999-01-20 2000-11-16 Heimann Systems Sa Systeme de discrimination de matieres organiques et inorganiques
US6928131B2 (en) * 2001-11-08 2005-08-09 Ratec, Ltd. Method for detecting an explosive in an object under investigation
US7162005B2 (en) 2002-07-19 2007-01-09 Varian Medical Systems Technologies, Inc. Radiation sources and compact radiation scanning systems
US7672422B2 (en) 2002-07-24 2010-03-02 Varian Medical Systems, Inc. Radiation scanning of objects for contraband
US7369640B2 (en) 2002-07-24 2008-05-06 Varian Medical Systems Technologies, Inc. Radiation scanning of objects for contraband
US7103137B2 (en) 2002-07-24 2006-09-05 Varian Medical Systems Technology, Inc. Radiation scanning of objects for contraband
US7164747B2 (en) 2002-10-02 2007-01-16 Reveal Imaging Technologies, Inc. Folded array CT baggage scanner
US7224765B2 (en) 2002-10-02 2007-05-29 Reveal Imaging Technologies, Inc. Computed tomography system
US7123681B2 (en) 2002-10-02 2006-10-17 L-3 Communications Security And Detection Systems, Inc. Folded array CT baggage scanner
US7356115B2 (en) 2002-12-04 2008-04-08 Varian Medical Systems Technology, Inc. Radiation scanning units including a movable platform
US7313221B2 (en) 2002-12-10 2007-12-25 Commonwealth Scientific And Industrial Research Organization Radiographic equipment
CN1723388B (zh) * 2002-12-10 2011-01-26 联邦科学和工业研究委员会 射线照相设备
US7046761B2 (en) 2003-01-23 2006-05-16 Reveal Imaging Technologies, Inc. System and method for CT scanning of baggage
US7333589B2 (en) 2003-01-23 2008-02-19 Reveal Imaging Technologies System and method for CT scanning of baggage
WO2004090576A2 (fr) * 2003-04-02 2004-10-21 Reveal Imaging Technologies, Inc. Systeme et procede de resolution des menaces dans la detection automatisee des explosifs a l'interieur des bagages et autres colis
US7116751B2 (en) 2003-04-02 2006-10-03 Reveal Imaging Technologies, Inc. System and method for resolving threats in automated explosives detection in baggage and other parcels
WO2004090576A3 (fr) * 2003-04-02 2005-03-03 Reveal Imaging Technologies In Systeme et procede de resolution des menaces dans la detection automatisee des explosifs a l'interieur des bagages et autres colis
US7440537B2 (en) 2003-10-02 2008-10-21 Reveal Imaging Technologies, Inc. Folded array CT baggage scanner
US7702068B2 (en) 2004-02-11 2010-04-20 Reveal Imaging Technologies, Inc. Contraband detection systems and methods
US7440544B2 (en) 2004-02-11 2008-10-21 Reveal Imaging Technologies, Inc. Contraband detection systems and methods
US7679065B2 (en) 2004-08-06 2010-03-16 Commonwealth Scientific And Industrial Research Organisation Data display system and method
CN101036160B (zh) * 2004-08-06 2011-06-29 澳联邦科学与工业研究组织 数据显示系统和方法
WO2006012703A1 (fr) * 2004-08-06 2006-02-09 Commonwealth Scientific And Industrial Research Organisation Systeme et procede d'affichage de donnees
US7897934B2 (en) 2004-08-12 2011-03-01 John Sved Process for neutron interrogation of objects in relative motion or of large extent
US7663119B2 (en) 2004-08-12 2010-02-16 John Sved Process for neutron interrogation of objects in relative motion or of large extent
WO2007130857A3 (fr) * 2006-05-05 2008-03-13 American Science & Eng Inc Tomodensitométrie combinée à rayons x/système d'identification à neutrons
WO2007130857A2 (fr) * 2006-05-05 2007-11-15 American Science And Engineering, Inc. Tomodensitométrie combinée à rayons x/système d'identification à neutrons
US7864920B2 (en) 2006-05-05 2011-01-04 American Science And Engineering, Inc. Combined X-ray CT/neutron material identification system
US7551714B2 (en) 2006-05-05 2009-06-23 American Science And Engineering, Inc. Combined X-ray CT/neutron material identification system
EP2259092A3 (fr) * 2009-06-02 2012-03-28 Applied Signal Technology Inc. Système d'inspection pour déterminer la composition du contenu d'un article
US8395124B2 (en) 2009-06-02 2013-03-12 Raytheon Applied Signal Technology, Inc. Article inspection system and method
CN102279141A (zh) * 2010-06-12 2011-12-14 中国民航科学技术研究院 用于检测ct型安全检查设备的测试箱
CN102279141B (zh) * 2010-06-12 2013-05-01 中国民航科学技术研究院 用于检测ct型安全检查设备的测试箱
US9746583B2 (en) 2014-08-27 2017-08-29 General Electric Company Gas well integrity inspection system
WO2023065671A1 (fr) * 2021-10-18 2023-04-27 同方威视技术股份有限公司 Système et procédé de détection entièrement automatique
WO2024064896A1 (fr) * 2022-09-22 2024-03-28 Analogic Corporation Détermination de propriétés physiques d'éléments introduits dans un système de balayage à rayons x, et systèmes, procédés et appareils associés

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MX9703225A (es) 1998-03-31
IL115789A (en) 1998-09-24
IL115789A0 (en) 1996-01-19

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