Contraband detection apparatus and method

• US 5,606,167 A
• Filed: 01/31/1995
• Issued: 02/25/1997
• Est. Priority Date: 07/11/1994
• Status: Expired due to Term

• Current Assignee: Thomas G. Miller
• Original Assignee: Thomas G. Miller
• Inventors: Miller, Thomas G.
• Primary Examiner(s): Hannaher, Constantine
• Application Number:
  US08/380,953
• Time in Patent Office: 756 Days
• Field of Search: 250/390.04, 250/390.05, 250/390.06, 250/390.07, 250/390.08, 250/390.11, 250/390.12
• US Class Current: 250/390.04
• CPC Class Codes: G01N 23/09 the radiation being neutrons
• CPC Class Codes: G01T 1/201 using scintillating fibres
• CPC Class Codes: G01T 3/06 with scintillation detectors
• CPC Class Codes: G01V 5/22 Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays

Abstract

A contraband detection system (18) using a single, cone shaped neutron beam determines substances concealed in a sample object by developing total neutron cross section spectra for a plurality of elements, including carbon, nitrogen, oxygen, hydrogen and other potential contraband-indicating elements. A processor (26) performs a contraband determination classification based on the neutron total cross section spectra for the plurality of elements, including hydrogen and elements which do not have peaks in the energy range of interest. The contraband detection system (18) includes a neutron source (20) for producing a pulsed, cone shaped beam of fast white neutrons; a spatial neutron detection array (40); a conveyor system (28) for situating a sample object (29) between the source (20) and the detection array (40); a spectra analysis system (24) for determining the neutron total cross section spectra of elements located in the sample object; and the processor (26). The neutron source (20) produces a pulsed beam (36) of fast white neutrons having sufficient energy range whereby removal of neutrons from the beam caused by the presence of a plurality of contraband-indicating elements can be determined. Various techniques of making contraband classification determinations are also disclosed.

Claims

1. Apparatus for detecting a contraband substance internally located in a sample object, wherein all portions of the sample object may be analyzed simultaneously through the use of a single beam of neutrons, the apparatus comprising:

means for producing a pulsed beam of fast white neutrons from a point source, which beam expands to a conical shape and has sufficient intensity in a range over several MeV, so that a plurality of elements have one or more resonance peaks in such energy range;

means for detecting neutrons, which means includes one or more neutron detectors;

means for measuring the time of flight of neutrons from said point source to the said detecting means;

means for situating a sample object between the neutron producing means and the detecting means at a point at which the said neutron beam has expanded sufficiently to allow neutrons in the beam to contact all portions of the sample object sought to be analyzed;

means for determining the neutron attenuation spectra of each portion of the sample object encompassing a solid angle between said point source and a detector of the said detector means; and

means for making a classification determination based upon said neutron attenuation spectra regarding a potential contraband substance located in the sample object.

2. The apparatus of claim 1, wherein the means for detecting neutrons comprises neutron detectors configured to form a curved surface, so that each said detector is on a straight line and approximately equidistant from the said white neutron point source.

3. The apparatus of claim 1, further comprising processing means for evaluating the neutron attenuation spectra for each portion of the sample object encompassing a solid angle between said point source and a detector of the said detector means for the plurality of contraband-indicating elements, by using the measured attenuation spectra and the total cross sections of the elements in the sample object and determining or imaging the concentrations or number densities of a plurality of elements located in the sample object, and for making a classification determination regarding a potential contraband substance located in the sample object.

4. The apparatus of claim 1, further comprising processing means for evaluating the neutron attenuation spectra for each portion of the sample object encompassing a solid angle between said point source and a detector of the said detector means for the plurality of contraband-indicating elements, including elements which do not have a resonance peak in the energy range of said neutron beam such as hydrogen, and determining or imaging the concentrations or number densities of a plurality of elements located in the sample object, and for making a classification determination regarding a potential contraband substance located in the sample object.

5. The apparatus of claim 1, wherein the said means for determining the neutron attenuation spectra consists of a central processing unit which executes instructions for taking the natural log of the ratios of the neutron flux of the beam (as a function of neutron energy) when the sample object is not in the beam and the neutron flux of the beam (as a function of neutron energy) when the sample object is in the beam.

6. The apparatus of claim 1, wherein the said means of making the classification determination regarding the presence of a contraband substance consists of one or more neural networks trained to recognize neutron attenuation spectra of objects containing contraband substances.

7. Apparatus for detecting a contraband substance internally located in a sample object, the apparatus comprising:

(1) means for producing a pulsed beam of fast white neutrons from a point source in an energy range over several MeV, so that a plurality of elements, including but not limited to carbon, nitrogen, and oxygen, have one or more resonance peaks in such energy range;

(2) means for detecting neutrons, including neutrons in the said white neutron beam, with or without a sample object in said beam, and for determining which neutrons are not removed from the beam when a sample object is in the beam;

(3) means for situating a sample object between the neutron producing means and the detecting means;

(4) means for evaluating the neutron attenuation spectra for the sample object; and

,

(5) processing means for evaluating the neutron attenuation spectra to determine the potential presence of hydrogen in the sample object, or the presence of other elements in the sample object which do not have a resonance peak in the energy range of interest, where the processing means further uses the neutron attenuation spectra evaluation and the determination of the potential presence of hydrogen or other such element not containing a resonance peak to make a classification determination regarding a potential presence of a contraband substance located in the sample object.

8. The apparatus of claim 7, wherein the means for detecting neutrons comprises neutron detectors, configured to form a curved surface, so that each said detector is on a straight line and approximately equidistant from the said white neutron point source.

9. The apparatus of claim 7, wherein the processing means uses the said neutron removal spectra evaluation and the determination of the potential presence of hydrogen, or another element which does not have a resonance peak in the energy range of interest, to make a classification determination regarding a potential presence of a contraband substance located in the sample object, through evaluating the following expression:

##EQU1## Where;

N_o =Neutron spectra without sample object in neutron beam

N=Neutron spectra with sample object in neutron beam

C_i =i^th Channel of the multi-channel analyzer

σ

_j =Total cross sections of the j^th element

α

_j =Atoms per cm² of j^th element in the neutron beam,

using linear regression or other method to evaluate α

, wherein the number of elements is given by j and where α

₁ represents the number density of hydrogen, or another element which does not have a resonance peak in the energy range of interest, and the remaining α

_j represent the number densities of other contraband indicating elements;

for example without limitation α

₁ would represent the number density of hydrogen atoms density per square cm, α

₂ could represent the number density of carbon in atoms per square cm, α

₃ could represent the number density of nitrogen atoms in per square cm, and α

₄ could represent the number density of oxygen in atoms per square cm in the neutron beam;

processing means for determining the atomic ratios of contraband-indicating elements, including without limitation C/O, N/O, H/C, and NO/CH;

processing means for determining if said measured atomic ratios match or approximate the same atomic ratios of such elements in known contraband substances; and

means for sounding an alarm to denote the presence of contraband if said measured atomic ratios match or approximate the same atomic ratios of such elements in known contraband substances.

10. Method of detecting a contraband substance internally located in a sample object, comprising the steps of measuring the neutron attenuation spectra of all portions of a sample object simultaneously, evaluating said neutron attenuation spectra, and making a classification determination on the basis of such neutron attenuation spectra regarding whether there is a contraband substance internally located in the sample object.

11. The method of claim 10, wherein the step of measuring said neutron attenuation spectra includes producing a pulsed white neutron beam which has sufficient intensity in a range over several MeV so that a plurality of contraband-indicating elements have one or more resonance peaks in such energy range and which beam is caused to expand from a point source in a conical shape to encompass the portions of the sample object sought to be analyzed;

configuring a plurality of neutron detectors to form a curved surface such that each such neutron detector is on a straight line and approximately equidistant from said point source;

measuring the time of flight of neutrons in said beam from said point source to said detectors; and

determining the neutron attenuation spectra on the basis of such time of flight measurements.

12. The method of claim 11, wherein the step of measuring said neutron attenuation spectra includes measuring the neutron flux of the beam (as a function of neutron energy) when the sample object is not in the beam and measuring the neutron flux of the beam (as a function of neutron energy) when the sample object is in the beam, and then taking the natural log of the ratios of such neutron flux measurements to determine the neutron attenuation spectra.

13. The method of claim 10, wherein the steps of evaluating the neutron spectra and making a classification determination regarding the presence of a contraband substance are performed by one or more neural networks trained to recognize attenuation spectra of objects containing contraband substances.

14. The method of claim 10, wherein the step for evaluating the neutron spectra includes determining or imaging the number densities of the atoms of a plurality of contraband-indicating elements located in the sample object, including hydrogen or other elements which do not have a resonance peak in the energy range of interest, based upon said neutron attenuation spectra and wherein the step of making said classification determination includes comparing the ratios of said number densities of the contraband-indicating elements in such sample object with the known number density ratios of such elements in contraband substances.

15. The method of claim 10, wherein the step of evaluating said neutron attenuation spectra includes using such neutron attenuation spectra along with known total cross sections of contraband-indicating elements to determine or image the number densities of contraband-indicating elements in the sample object, and wherein the step of making the said classification determination includes comparing the measured number densities of contraband-indicating elements in the sample object to known number densities of such elements in contraband substances.

16. The method of claim 10, wherein the step of evaluating said neutron attenuation spectra includes determining the number densities of contraband-indicating elements in the sample object which do not have a resonance peak in the energy range of said neutron beam, such as hydrogen, and the step of making a classification determination regarding a potential contraband substance includes using the absence or presence and amount of hydrogen in the sample object as a basis for the classification determination.

17. The method of claim 10, wherein the step of evaluating the said neutron attenuation spectra includes using known total cross sections of contraband-indicating elements to determine the number densities of elements in the said sample object by using the following expression:

##EQU2## Where;

N_o =Neutron spectra without sample object in neutron beam

N=Neutron spectra with sample object in neutron beam

C_i =i^th Channel of the multi-channel analyzer

σ

_j =Total cross sections of the j^th element

α

_j =Atoms per cm² of j^th element in the neutron beam

using linear regression or other method known in the prior art to evaluate α

, wherein the number of elements is given by j and where α

₁ represents hydrogen, or another element which does not have a resonance peak in the energy range of interest, and the remaining α

_j represent the number densities of other contraband-indicating elements, and thereby obtaining the number densities of contraband-indicating elements located in the sample object; and

wherein the step of making a classification determination includes determining the various ratios of H, C, N, and O contained in the sample object, including without limitation C/O, N/O, H/C, and NO/CH, and comparing said measured atomic ratios to known atomic ratios of such contraband-indicating elements in known contraband substances.

18. Method of detecting a contraband substance internally located in a sample object, comprising the steps of measuring the neutron attenuation spectra of all portions of a sample object, evaluating said neutron attenuation spectra to identify contraband-indicating elements which do not have a resonance peak in the energy range of said neutron attenuation spectra, including hydrogen, and making a classification determination on the basis of such neutron attenuation spectra and absence or presence and amount of said elements which do not have a resonance peak within the energy ranges in said attenuation spectra, including hydrogen, regarding whether there is a contraband substance internally located in the sample object.

19. Apparatus for detecting a contraband substance internally located in a sample object, wherein all portions of the sample object may be analyzed simultaneously through the use of a single beam of neutrons, the apparatus comprising:

(i) an accelerator for generating a pulsed deuteron beam and for directing the pulsed deuteron beam to a target;

(ii) a target with a composition such that impingement of the pulsed deuteron beam produces a single pulsed beam of neutrons which expands in a conical shape from a point source;

(iii) a neutron detector array;

(iv) a conveying system for introducing a sample object, such as a suitcase, between the neutron source and the neutron detector assembly;

(v) a spectra analysis system; and

(vi) a processor for evaluating the said neutron attenuation spectra for the plurality of contraband-indicating elements and for making a classification determination regarding a potential contraband substance located in the sample object.

20. The apparatus of claim 19, wherein the said accelerator is capable of producing a pulsed deuteron beam from 4-7 MeV with a beam width of 1 nanosecond with a repetition rate of 1-3 MHz:

the said target consists of a composition such that impingement of the pulsed deuteron beam produces a pulsed white neutron beam with a relatively flat neutron distribution around 0 degrees which expands in the shape of a cone;

the said neutron detector array is comprised of an θ

-φ

array of a plurality of neutron detector assemblies, wherein each such assembly is comprised of a neutron detector element, a photomultiplier tube, and a voltage divider connected through an amplifier to a spectral analysis system;

the said spectra analysis system consists of a deuteron beam pick-off, a time pick-off, an array of time-to-amplitude converters (TACs), a multi-channel analyzer array, and a background gamma ray reduction circuit; and

the said processor consists of a conventional data processing system having a central processing unit, memory, an arithmetic logic unit, and an input/output interface/controller which is connected to a printer, a CRT display screen, and an alarm.