NUCLEAR TECHNIQUES FOR DETECTING THE PRESENCE OF EXPLOSIVES

• US 3,832,545 A
• Filed: 09/28/1972
• Issued: 08/27/1974
• Est. Priority Date: 09/28/1972
• Status: Expired due to Term

• Current Assignee: John Bartko
• Original Assignee: John Bartko
• Inventors: Bartko, John
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Dixon, Harold A.
• Application Number:
  US05/290,901
• Time in Patent Office: 698 Days
• Field of Search: 250/83.3R,71.5R,16T,312,359,367,492
• US Class Current: 376/159
• CPC Class Codes: G01V 5/20 Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects
• CPC Class Codes: G01V 5/234 Measuring induced radiation, e.g. thermal neutron activation analysis

Abstract

The invention pertains to a nuclear technique for monitoring objects such as luggage and parcels to determine the presence of specified nitrogen containing materials such as explosives as a function of the nitrogen content and concentration profile. Objects to be analyzed to determine the presence of nitrogen are subjected to a thermal neutron environment and the gamma ray radiation produced by the object in response to nitrogen reactions is monitored by gamma ray detectors. The gamma ray detectors produce indications of the nitrogen content of the object and the concentration profile of the nitrogen in the object. The information provided by the gamma ray detectors is processed to determine if the measured nitrogen content and concentration corresponds to a class of nitrogen containing material of interest, i.e. explosives.

Claims

1. Apparatus for monitoring discrete portions of an object to determine the concentration of nitrogen in the respective portions and to develop output signals indicative of the concentration of nitrogen in the respective portions to permit the development of the nitrogen concentration profile of the object, comprising, first means for subjecting an object to a thermal neutron environment, second means including an array of gamma detectors each positioned to view a predetermined portion of said object and produce an output signal indicative of the nitrogen present within the respective portion of said object in response to the gamma ray energy proDuced by reactions between the nitrogen contained in said portion of the object and the thermal neutron environment, each of said gamma detectors including a scintillator having an end surface for viewing said respective portion of said object, the length of said scintillator being substantially greater than the effective diameter of the end surface, and third means operatively connected to said second means for determining the level of gamma radiation emitted from each of a plurality of predetermined portions of said object.

2. Apparatus as claimed in claim 1 wherein said first means includes a fast neutron source comprised of californium 252, and a neutron moderator.

3. Apparatus as claimed in claim 1 wherein said third means includes means associated with said plurality of gamma detectors to respond to the output signals of said gamma detectors to characterize the output of each of said gamma detectors as a pulse of a different predetermined width, the number of pulses produced by each gamma detector being a function of the nitrogen content of the corresponding discrete portion of said object.

4. Apparatus as claimed in claim 3 further including means for identifying each of said gamma detectors according to said pulse width and producing a representation of the array of said gamma detectors illustrating the nitrogen concentration profile of said object as a function of the number of pulses associated with the respective gamma detectors.

5. Apparatus as claimed in claim 4 further including means for excluding pulses having a magnitude less than 10 MeV.

6. Apparatus as claimed in claim 4 wherein said array of gamma detectors is an X-Y array having a plurality of vertical columns and a plurality of horizontal rows.

7. Apparatus as claimed in claim 6 wherein said means for identifying determines the vertical dimension of the nitrogen concentration profile by monitoring the number of pulses appearing in the rows of said gamma detectors and the horizontal dimension of the nitrogen concentration profile by monitoring the number of pulses present in the columns of gamma detectors.

8. Apparatus as claimed in claim 1 wherein said nitrogen reaction is 14N(n, Nu )15N.

9. Apparatus as claimed in claim 1 further including a second array of a plurality of gamma detectors identical to the other array and being positioned in opposed, aligned relationship such that one gamma detector from each array view the same portion of said object, said combination of arrays being adapted to receive said object between said aligned group.

10. Apparatus as claimed in claim 9 wherein the output signal of the gamma detectors forming each aligned pair are combined for application to said third means.

11. Apparatus as claimed in claim 1, wherein said scintillator is a plastic or liquid scintillator.

12. Apparatus as claimed in claim 1 further including a total nitrogen content measuring means operatively connected to said third means to respond to the electrical to determine the total nitrogen content of said object.

13. Apparatus as claimed in claim 1 and further including means operatively connected to said third means for defining the nitrogen concentration profile of the nitrogen containing material of said object in response thereto.

14. Apparatus as claimed in claim 13 further including means for comparing the nitrogen concentration profile of said nitrogen containing material with nitrogen concentrations profiles of known materials in order to classify the nitrogen containing material of said object.

15. Apparatus as claimed in claim 1 wherein said array further includes at least one gamma detector including a scintillator having an end viewing surface of an effective diameter of five inches or greater for viewing said object and providing an indication of the total nitrogen content of said object.

16. Apparatus as claimed in claim 15 further including means operatively connected to said third means for classIfying the nitrogen containing object on the basis of the total nitrogen content and the nitrogen concentration profile of said object.

17. Apparatus as claimed in claim 1 wherein said first means includes a housing comprised of a neutron moderator material and having a cavity therein for accommodating said object, and a source of fast neutrons positioned within said housing to provide thermal neutron flux within said cavity, said plurality of individual gamma detectors positioned within said housing, each of said gamma detectors viewing a predetermined portion of said object within said cavity and producing an output signal indicative of the nitrogen contained within the respective portion of said object.

18. Apparatus as claimed in claim 8 wherein said cavity is in the form of a passage extending through said housing and further including means for inserting and removing said object in said passage.

19. Apparatus as claimed in claim 18 wherein said means for inserting and removing said object includes spaced apart, vertically disposed members comprised of a neutron moderator material, said spaced apart vertically disposed members define a volume suitable for accommodating said object, said spaced apart vertically disposed members functioning to effectively close the open ends of said passage and cooperate with the walls of said passage to define substantially enclosed thermal neutron flux environment to which said object is subjected.

20. Apparatus as claimed in claim 18 further including means operatively connected to said third to reset said third means in response to the passage of each object.

21. Apparatus as claimed in claim 20 wherein said third means is reset in response to the passage of said spaced apart, vertically disposed members.