Method for detecting an explosive in an object under investigation

• US 6,928,131 B2
• Filed: 04/24/2002
• Issued: 08/09/2005
• Est. Priority Date: 11/08/2001
• Status: Expired due to Fees

• Current Assignee: "Scientific and Technical Center Inntech" Limited
• Original Assignee: Ratec LLC
• Inventors: Gjibovski, Nikolai Erikovich, Philippov, Sergey Galievich, Olshansky, Yury Iosiphovich
• Primary Examiner(s): Carone, Michael J.
• Assistant Examiner(s): PALABRICA, RICARDO J
• Application Number:
  US10/221,819
• Publication Number:
  US 20030147484A1
• Time in Patent Office: 1,203 Days
• Field of Search: 376/157, 376/158, 376/166, 376/159, 250/370.09, 250/390.01, 250/390.04, 378/57, 378/53
• US Class Current: 376/158
• CPC Class Codes: G01N 23/04 and forming images of the material
• CPC Class Codes: G01N 23/222 using neutron activation analysis [NAA]
• CPC Class Codes: G01V 5/223 Mixed interrogation beams, e.g. using more than one type of radiation beam
• CPC Class Codes: G01V 5/234 Measuring induced radiation, e.g. thermal neutron activation analysis
• CPC Class Codes: G21K 5/10 with provision for relative movement of beam source and object to be irradiated

Abstract

A method for detecting an explosive in an object under investigation involves the initial X-ray irradiation of the object under investigation, e.g. a piece of luggage or mailing, and forming its X-ray images; using the X-ray images to detect areas with a high density of organic materials and identifying articles therein; determining the location, dimensions and supposed mass of an unidentified article; determining and forming a directional pattern of the neutron radiator corresponding to the dimensions of the unidentified article. The method further includes subsequent thermal neutron irradiation of the area with the unidentified article; recording gamma-ray quanta having the energy of 10.8 MeV and cascade gamma-ray quanta with energies of 5.534 and 5.266 MeV by at least two gamma-ray detectors; counting of simultaneously recorded pairs of cascade gamma-ray quanta; determination of the overall gamma-ray intensity, taking into account weight factors in readings of the detectors; determination of the threshold value for the overall gamma-ray intensity basing on the supposed mass of explosive being detected; and making a decision in the event the threshold value of overall gamma-ray intensity is exceeded. When checking small-size objects, the neutron irradiation step is preceded by replacing the ambient air by a gaseous medium not containing nitrogen.

Claims

1. A method for detecting an explosive in an object under investigation, comprising the following steps:

(a) initially exposing the object under investigation to X-rays for purposes of detecting whether the object contains a nitrogen-containing explosive having an average density range of 1.25 to 2.00 g/cm³;

(b) recording the X-rays that have passed through the object under investigation;

(c) finding areas of the object under investigation with a density of organic materials exceeding a pre-established value, on a basis of a value of X-ray attenuation;

(d) identifying articles contained in the aforementioned found areas of the object under investigation with said density of organic materials higher than the pre-established value, on a basis of an analysis of said recorded X-rays;

(e) selecting among said areas of the object under investigation an area containing an unidentified article;

(f) in case all the articles are identified as not containing a nitrogen-containing explosive having an average density range of 1.25 to 2.00 g/cm³ the process of detecting is stopped;

(g) in case any article is unidentified the method of detecting further comprising;

(h) determining the dimensions and position of said unidentified article in the object under investigation, on a basis of an analysis of said recorded X-rays;

(i) evaluating a mass of a nitrogen-containing explosive being detected based on an average density range of 1.25 to 2.00 g/cm³ which corresponds to said dimensions of the unidentified article;

(k) exposing to thermal neutrons the selected area of the object under investigation containing the unidentified article;

(l) recording, using at least two gamma-ray detectors, gamma-ray quanta with the energy of 10.8 MeV and pairs of simultaneously emitted cascade gamma-ray quanta emitted by said area of the object under investigation exposed to thermal neutrons;

(m) counting pairs of said cascade gamma-ray quanta recorded simultaneously;

(n) determining the overall intensity of gamma rays emitted by the object under investigation;

(o) determining a threshold value for said overall intensity of gamma rays emitted by the object under investigation, on a basis of said evaluated mass of the explosive being detected which corresponds to the dimensions of the unidentified article;

(p) making a decision about presence of a nitrogen-containing explosive having an average density range of 1.25 to 2.00 g/cm³ in the object under investigation in the event that said overall intensity of gamma rays emitted by the object under investigation exceeds the said threshold value.

2. A method as set forth in claim 1, wherein said exposure to thermal neutrons of said area of the object under investigation that contains an unidentified article is carried out using a controlled thermal neutron radiator with a variable thermal neutron fluence pattern, which controlled thermal neutron radiator is based on the deuterium-deuterium reaction and is equipped with a neutron moderator.

3. A method as set forth in claim 1, wherein when said recording of the cascade gamma-ray quanta the gamma-ray quanta having the energies of 5.534 MeV and 5.266 MeV are recorded.

4. A method as set forth in claim 1, wherein said determination of overall intensity of gamma rays emitted by the object under investigation is carried out by summing up the numbers of recordings of said 10.8 MeV gamma-ray quanta by each of said gamma-ray detectors multiplied by a weight factor of readings of detector, and the numbers of pairs of said cascade gamma-ray quanta, simultaneously recorded by each of pairs of said gamma-ray detectors, multiplied by weight factor of readings of the pair of detectors.

5. A method as set forth in claim 4, wherein said determination of the weight factor for readings of a pair of detectors is carried out as the arithmetic mean of said weight factors of readings of detectors composing said pair.

6. A method as set forth in claim 1, which includes a reduction of the mass of air surrounding the object under investigation by means other than physical location of said thermal neutron radiator or gamma-ray detectors prior to said exposure to thermal neutrons.

7. A method as set forth in claim 1 which includes a reduction of the mass of air surrounding the object under investigation wherein said reduction of the mass of air surrounding the object under investigation is carried out through air displacement.

8. A method as set forth in claim 7, wherein said exposure to thermal neutrons of said area of the object under investigation that contains an unidentified article is carried out using a controlled thermal neutron radiator with a variable directional pattern, which controlled thermal neutron radiator is based on the deuterium-deuterium reaction and is equipped with a neutron moderator.

9. A method as set forth in claim 7, wherein when said recording of the cascade gamma-ray quanta the gamma-ray quanta having the energies of 5.534 MeV and 5.266 MeV are recorded.

10. A method as set forth in claim 7, wherein said determination of overall intensity of gamma rays emitted by the object under investigation is carried out by summing up the numbers of recordings of said 10.8 MeV gamma-ray quanta by each of said gamma-ray detectors multiplied by a weight factor of readings of detector, and the numbers of pairs of said cascade gamma-ray quanta, simultaneously recorded by each of pairs of said gamma-ray detectors, multiplied by weight factor of readings of the pair of detectors.

11. A method as set forth in claim 10, wherein said determination of the weight factor for readings of a pair of detectors is carried out as the arithmetic mean of said weight factors of readings of detectors composing said pair.

12. A method as set forth in claim 7, wherein said air displacement is carried out with the use of a gaseous medium not containing nitrogen.