Multi-sensor explosive detection system

• US 5,078,952 A
• Filed: 01/10/1990
• Issued: 01/07/1992
• Est. Priority Date: 06/16/1989
• Status: Expired due to Term

• Current Assignee: Rapiscan Laboratories Incorporated (OSI Systems Incorporated)
• Original Assignee: Science Applications International Corporation
• Inventors: Shea, Patrick M., Sawa, Z. Peter, Gozani, Tsahi
• Primary Examiner(s): Walsh, Donald P.
• Assistant Examiner(s): Chelliah, Meena
• Application Number:
  US07/463,036
• Time in Patent Office: 727 Days
• Field of Search: 376/159, 376/161, 376/158, 382/16, 382/17, 364/513
• US Class Current: 376/159
• CPC Class Codes: G01N 23/222 using neutron activation analysis [NAA]
• CPC Class Codes: G01V 5/234 Measuring induced radiation, e.g. thermal neutron activation analysis
• CPC Class Codes: Y10S 706/933 Law, law enforcement, or government

Abstract

A nuclear detection system and method efficiently detects explosives in checked airline baggage or other parcels with a high probability of detection (PD) and a low probability of false alarms (PFA). The detection system detects the presence of nitrogen and its rough density distribution within the object under investigation by performing a nuclear-based analysis of the object. The detection system includes a source of thermal neutrons; an array of gamma ray detectors; a neutron detector; means for irradiating the object being examined to neutrons from the neutron source, which neutrons interact with the atomic nuclei of one or more specific elements, e.g., nitrogen, chlorine, or hydrogen present within the object so as to cause elemental-specific gamma rays to be emitted; means for capturing and counting the elemental-specific gamma rays and determining their approximate origin within the object, thereby providing a rough measure of the density distribution of these specific elements within the object; and means for detecting neutrons that pass through the object without substantially interacting with atomic nuclei, thereby providing an image of the atomic density distribution of the object similar to conventional neutron radiography. One embodiment of the invention includes an artificial neural system (ANS) of analyzing the recorded gamma rays and efficiently discriminating between objects carrying explosives and objects not carrying explosives. Another embodiment utilizes a spectral correlation method (SCM) to remove undesirable background noise from the spectrum of detected gamma rays. Still another embodiment uses a X-ray system to generate an electron density image of the object being investigated, which electron density image helps confirm the presence of explosives within the object.

Claims

1. An explosive detection system comprising:

(a) a source of neutrons;

(b) a detector array comprising a plurality of gamma ray detectors, each of said gamma ray detectors providing a detection signal in the event a gamma ray is captured by said detector, and at least one neutron detector, said neutron detector providing a neutron detection signal in the event a neutron is captured by said neutron detector;

(c) means for irradiating an object being examined with neutrons from the neutron source and for positioning the detector array relative to the object so that gamma rays emitted from the elements within the object as a result of said neutron irradiation are detected by the gamma ray detectors of said detector array; and

(d) parallel distributed processing means responsive to the detection signals of said detector array for discriminating between objects carrying explosives and objects not carrying explosives, said parallel distributed processing means including an artificial neural system (ANS), said ANS having a parallel network of processors, each processor of said parallel network of processors including means for receiving at least one input signal, and means for generating an output signal as a function of said at least one input signal.

2. The explosive detection system as set forth in claim 1 further including spectral correlation means for removing noise from the gamma ray detection signals generated by said gamma ray detectors, whereby only gamma rays having a selected energy level are accepted by said parallel distributed processing means.

3. The explosive detection system as set forth in claim 1 further including X-ray means for generating an electron density image of said object, said means for utilizing said electron density image in combination with the detection signals from said detector array to discriminate between objects carrying explosives and objects not carrying explosives.

4. The explosive detection system as set forth in claims 1, 2, or 3 wherein said parallel network of processors includes a plurality of layers of said processors, a first layer of said processors receiving as an input signal a detection signal from one of said plurality of detectors, a last layer of said processors providing a plurality of output signals that classify said objects as objects carrying explosives and objects not carrying explosives.

5. The explosive detection system as set forth in claim 4, further including means for applying an adjustable weighting factor to the at least one input signal of each processor, whereby the output signals that classify said objects can be adjusted to properly classify said objects through adjustment of said weighting factors.

6. The explosive detection system as set forth in claims 1, 2 or 3 wherein said parallel network of processors includes a plurality of layers of said processors, a first layer of said processors receiving as an input signal a feature signal derived from a selected combination of said detector signals, a last layer of said processors providing a plurality of output signals that classify said objects as objects carrying explosives and objects not carrying explosives.

7. The explosive detection system as set forth in claim 6 further including means for applying an adjustable weighting factor to the at least one input signal of each processor, whereby the output signals that classify said objects can be adjusted to properly classify said objects through adjustment of said weighting factors.

8. An explosive detection system comprising:

(a) a source of neutrons;

(b) at least one detector array comprising a plurality of gamma ray detectors, each of said detectors providing a detection signal in the event a gamma ray is captured by said detector;

(d) a neutron detector;

(c) means for bombarding an object being examined with neutrons from the neutron source and for positioning the detector array relative to the object so that gamma rays emitted from the elements within the object as a result of said neutron bombardment are detected by the gamma ray detectors of said detector array; and

(d) parallel distributed processing means responsive to the detection signals of said detector array and neutron detector for discriminating between objects carrying explosives and objects not carrying explosives, said parallel distributed processing means comprising a parallel network of processors, each processor of said parallel network of processors including means for receiving at least one input signal, and means for generating an output signal as a function of said at least one input signal, said parallel network of processors including a plurality of layers of said processors, a first layer of said processors receiving as an input signal a feature signal derived from a selected combination of said detection signals, a last layer of said processors providing a plurality of output signals that classify said objects as either objects having a high probability of carrying explosives or objects having a high probability of not carrying explosives.

9. Apparatus for non-invasively detecting explosives in an object under investigation comprising:

means for generating thermal neutrons;

means for irradiating said object with said thermal neutrons, the interactions of said thermal neutrons with atomic nuclei within said object giving rise to the emission of gamma rays, said gamma rays having an energy level characteristic of the nuclear species contained in said object;

gamma ray detection means for detecting emitted gamma rays having an energy level characteristic of at least one element and for roughly determining the location within said object from which the detected gamma rays originated, the detection of said gamma rays and their source location thereby providing a measure of the density distribution of said at least one element within said object;

neutron detection means for detecting neutrons that pass through said object without interacting with atomic nuclei, the detection of said neutrons thereby providing a measure of the density distribution of all materials within said object, including said at least one element;

image means responsive to said gamma ray and neutron detection means for generating a three-dimensional density image of said at least one element within said object; and

an artificial neural system, said artificial neural system including recognition means responsive to said gamma ray and neutron detection means for recognizing a pattern of detected gamma rays and neutrons indicative of an explosive.

10. Explosive detection apparatus as set forth in claim 9 further including:

means for generating at least one two-dimensional electron density image of said object; and

means for combining said at least one element density image and said electron density image and for determining whether said combined image indicates the presence of explosives within said object.

11. Explosive detection apparatus as set forth in claim 10 wherein said electron density image generation means includes means for generating two two-dimensional electron density images of said object, a first electron density image lying in a first plane, and a second electron density image lying in a second plane that is orthogonal to said first plane.

12. Explosive detection apparatus as set forth in claim 9 wherein said recognition means of said artificial neural system includes means for automatically adjusting the patterns it recognizes as belonging to explosives based on detected patterns of gamma rays and neutrons from objects containing known explosives.

13. Explosive detection apparatus as set forth in claim 9 or 10 wherein said gamma ray detection means includes means for rejecting background noise in the detected gamma rays, said background noise including the detection of gamma rays emitted from non-explosive elements.

14. Explosive detection means as set forth in claim 13 wherein said means for rejecting background noise includes spectral correlation means for measuring background noise at a first location in the detected gamma ray spectrum and subtracting said background noise from a second location in the gamma ray spectrum, said second location in the gamma ray spectrum corresponding to gamma rays resulting from neutron interaction with nitrogen nuclei.

15. Apparatus for non-invasively detecting explosives in an object under investigation comprising:

means for generating thermal neutrons;

means for irradiating said object with said thermal neutrons, the interactions of said thermal neutrons with atomic nuclei within said object giving rise to the emission of gamma rays, said gamma rays having an energy level characteristic of the nuclear species contained in said object;

gamma ray detection means for detecting emitted gamma rays having an energy level characteristic of at least one specific element and for roughly determining the location within said object from which the detected gamma rays originated, the detection of said gamma rays and their source location thereby providing a measure of the density distribution of said at least one specific element within said object;

neutron detection means for detecting neutrons that pass through said object without interacting with atomic nuclei, the detection of said neutrons thereby providing a measure of the density distribution of all materials within said object, including said at least one element;

X-ray means for generating at least one two-dimensional electron density image of said object; and

determining means for combining said measure of the density distribution of all materials within said object, including said at least one specific element, with said electron density image, and for determining whether said combined measure and image indicate the presence of explosives within said object, said determining means including an artificial neural system, said artificial neural system having recognition means responsive to said gamma ray and neutron detection means for recognizing a pattern of detected gamma rays and neutrons indicative of an explosive.

16. Explosive detection apparatus as set forth in claim 15 wherein said electron density image generation means includes means for generating two two-dimensional electron density images of said object, a first electron density image lying in a first plane, and a second electron density image lying in a second plane that is orthogonal to said first plane.

17. Explosive detection apparatus as set forth in claim 15 wherein said recognition means of said artificial neural system includes means for automatically adjusting the patterns it recognizes as belonging to explosives based on detected patterns of gamma rays from objects containing known explosives.

18. Explosive detection apparatus as set forth in claim 15 wherein said artificial neural system is further responsive to the electron density images obtained from said X-ray means.

19. Explosive detection apparatus as set forth in claim 15 wherein said gamma ray detection means includes means for rejecting background noise in the detected gamma rays, said background noise including the detection of gamma rays emitted from non-explosive elements.

20. Explosive detection apparatus as set forth in claim 19 further including neutron detection means for detecting neutrons that pass through said object without interacting with atomic nuclei, the detection of said neutrons thereby providing a measure of the density distribution of all materials within said object, including nitrogen, hydrogen, and chlorine.

21. Apparatus for non-invasively detecting explosives in an object under investigation comprising:

means for generating thermal neutrons;

means for irradiating said object with said thermal neutrons, the interactions of said thermal neutrons with atomic nuclei within said object giving rise to the emission of gamma rays, said gamma rays having an energy level characteristic of the nuclear species contained in said object;

gamma ray detection means for detecting emitted gamma rays having an energy level characteristic of at least one specific element and for roughly determining the location within said object from which the detected gamma rays originated, the detection of said gamma rays and their source location thereby providing a measure of the density distribution of said at least one specific element within said object;

neutron detection means for detecting neutrons that pass through said object without interacting with atomic nuclei, the detection of said neutrons thereby providing a measure of the density distribution of all materials within said object, including said at least one element;

an artificial neural system, said artificial neural system including recognition means responsive to said gamma ray detection means for recognizing a pattern of detected gamma rays and neutrons indicative of an explosive, said recognition means including means for automatically adjusting the patterns it recognizes as belonging to explosives based on detected patterns of gamma rays and neutrons from objects containing known explosives;

image means responsive to said gamma ray detection means for generating a three-dimensional density image of said at least one specific element within said object;

determining means responsive to said artificial neural system and said image means for determining whether said three-dimensional density image of said at least one specific element density image indicates the presence of explosives within said object.

22. Explosive detection apparatus as set forth in claim 21 wherein said gamma ray detection means includes means for rejecting background noise in the detected gamma rays, said background noise including the detection of gamma rays emitted from non-explosive elements.

23. Explosive detection means as set forth in claim 22 wherein said means for rejecting background noise includes spectral correlation means for measuring background noise at a first location in the detected gamma ray spectrum and subtracting said background noise from a second location in the gamma ray spectrum, said second location in the gamma ray spectrum corresponding to gamma rays resulting from neutron interaction with nuclei.

24. Apparatus for non-invasively detecting explosives in an object under investigation comprising:

means for generating thermal neutrons;

means for irradiating said object with said thermal neutrons, the interactions of said thermal neutrons with atomic nuclei within said object giving rise to the emission of gamma rays, said gamma rays having an energy level characteristic of the nuclear species contained in said object;

gamma ray detection means for detecting emitted gamma rays having an energy level characteristic of at least one specific element and for roughly determining the location within said object from which the detected gamma rays originated, said gamma ray detection means including means for rejecting background noise in the detected gamma rays, said background noise including the detection of gamma rays emitted from non-explosive elements, the detection of said gamma rays and their source location thereby providing a measure of the density distribution of said at least one specific element within said object;

neutron detection means for detecting neutrons that pass through said object without interacting with atomic nuclei, the detection of said neutrons thereby providing a measure of the density distribution of all materials within said object, including said at least one element;

determining means responsive to said measure of the density distribution of the materials, including said at least one specific element, within said object for determining whether said object likely contains an explosive, said determining means including an artificial neural system.

25. Explosive detection means as set forth in claim 24 wherein said means for rejecting background noise within said gamma ray detection means includes spectral correlation means for measuring background noise at a first location in the detected gamma ray spectrum and subtracting said background noise from a second location in the gamma ray spectrum, said second location in the gamma ray spectrum corresponding to gamma rays resulting from neutron interaction with nuclei.