Explosive detection system

• US 5,114,662 A
• Filed: 12/14/1990
• Issued: 05/19/1992
• Est. Priority Date: 05/26/1987
• Status: Expired due to Term

• Current Assignee: Rapiscan Laboratories Incorporated (OSI Systems Incorporated)
• Original Assignee: Science Applications International Corporation
• Inventors: Gozani, Tsahi, Shea, Patrick M.
• Primary Examiner(s): Behrend, Harvey E.
• Application Number:
  US07/627,702
• Time in Patent Office: 522 Days
• Field of Search: 376/159, 376/157, 376/257
• US Class Current: 376/159
• CPC Class Codes: G01T 3/06 with scintillation detectors
• CPC Class Codes: G01V 5/226 using tomography
• CPC Class Codes: G01V 5/234 Measuring induced radiation, e.g. thermal neutron activation analysis

Abstract

A system for detecting the presence of explosives contained in an object under observation, including a cavity structure for receiving the object and a radiation source for producing thermal neutrons directed to the object under observation. Gamma rays are produced to represent the presence of explosives and as an example the concentration of nitrogen contained in the object. Inorganic scintillators are located within the cavity structure to detect the gamma rays and produce an output signal representative of the presence and concentration of the nitrogen and/or other elements contained in the object. The inorganic scintillators are formed as a ring around the cavity structure to detect the nitrogen and/or other elements within at least one particular plane passing through the object. The object under observation is moved through the cavity structure to detect the nitrogen in successive planes to build up a three dimensional profile of explosives concentration.

Claims

1. A method of producing a three dimensional profile of the concentration of a particular element in a particular object, including the following steps:

providing a cavity structure for receiving the particular object,

providing a source for producing thermal neutrons,

directing the thermal neutrons within the cavity structure to the object to interact with the particular element in the object to form gamma rays of a particular energy,

providing a plurality of detectors around the periphery of the cavity structure in a common plane with the thermal neutron source in the cavity structure and in a C-shaped ring configuration and in a closed loop with the thermal neutron source to detect the concentration of the particular element within the common plane, operating each of the detectors in said plurality of detectors independently of one another,

moving the object through the cavity structure in a direction transverse to the common plane to obtain the detection by the detectors of the presence of the particular element in successive planes of the object parallel to the common plane, processing the detections by the detectors of the particular element in the successive planes of the object parallel to the common plane to obtain the three dimensional profile of the concentration of the particular element within the object.

2. The method of claim 1 additionally including producing an alarm in response to the production of particular three dimensional profiles of the particular element in the object.

3. The method of claim 1 additionally including the detectors being composed of inorganic material.

4. The method of claim 3 wherein the inorganic detectors are provided from a group of materials including:

Sodium Iodide (NaI), Cesium Iodide (CsI), Bismuth Germanate (BGO-Bi₄ Ge₃ O₁₂) and Barium Floride (BaF₂), and solid-state detectors including Lithium-drifted Germanium (GE(Li)), High Purity Germanium (HPGe), and Mercuric Iodine (HgI₂).

5. The method of claim 4 wherein the inorganic detectors provided are formed from Sodium Iodide (NaI).

6. The method of claim 1 wherein the C-shaped ring defining the disposition of the detectors has an open end and the thermal neutron source is disposed in the open end of the C-shaped ring.

7. The method of claim 1 wherein the detectors are formed into a spaced pair of C-shaped rings each having an open end facing the open end in the other C-shaped ring and wherein the two C-shaped rings are spaced from each other in the direction of movement of the object and the two C-shaped rings are parallel to each other.

8. The method of claim 7 wherein each of the C-shaped rings is formed of parallel sets of individual detectors and the detections of the particular element by the detectors of the parallel sets of individual detectors are processed to obtain the three dimensional profile of the concentration of the particular element within the object.

9. A method of producing a three dimensional profile of the concentration of a particular element in a particular object, including the following steps:

providing a cavity structure for receiving the particular object,

producing thermal neutrons from a first source within the cavity structure from a stationary source to interact with the object within the cavity structure in forming gamma rays of a particular energy,

providing for a movement of the object through the cavity structure in a particular direction,

disposing a plurality of detectors within the cavity structure in a common plane with the thermal neutron source so as to enclose the object moving therethrough, said common plane being transverse to the particular direction of movement of the object through the cavity structure, independently producing output signals from each of the detectors representative of the gamma rays detected by such detector in each successive one of the transverse planes in the object as a result of the movement of the object in the particular direction in the cavity structure, and

processing the output signals from the detectors at progressive instants of time to obtain an indication of the three dimensional profile of the particular element in the object.

10. A method as set forth in claim 9, including the step of

producing an alarm when the indication of the three dimensional profile of the particular element in the object represents a particular concentration of the particular element in the object.

11. A method as set forth in either of claims 9 or 10 wherein

the transverse plane is perpendicular to the particular direction.

12. A method as set forth in either of claims 9 or 10 wherein

the detectors have an open configuration at one end of the transverse plane and wherein

the detectors constitute a first plurality and the thermal neutron source constitutes a first thermal neutron source and wherein

thermal neutrons are produced within the cavity structure from a second source displaced in the particular direction from the first source and wherein

a second plurality of detectors are disposed within the cavity structure with the second source in a plane parallel to the transverse plane for an independent production by each of such detectors of output signals representative of the gamma rays detected by such detector in each successive one of the transverse planes in the object as a result of the movement of the object in the particular direction in the cavity structure and wherein

the detectors in the second plurality have an open configuration int he plane defined by such detectors and the second neutron source at the end opposite the open end defined by the detectors in the first plurality and wherein

the output signals from the detectors in the first and second pluralities are processed at the progressive instants of time to obtain the indication of the three dimensional profile of the particular element in the object.

13. A method as set forth in either of claims 9 or 10 wherein

the thermal neutron source and the detectors are disposed in the cavity structure around the periphery of the cavity structure and wherein the detectors are disposed in a C-ring configuration having an open end and the thermal neutron source is disposed in the open end of the C-ring configuration.

14. A method as set forth in claim 12 wherein

the first thermal neutron source and the detectors in the first plurality are disposed in the cavity structure around the periphery of the cavity structure and wherein the detectors in the first plurality are disposed in a first C-ring configuration having an open end and the first thermal neutron source is disposed in the open end of the first C-ring configuration and wherein

the second thermal neutron source and the detectors in the second plurality are disposed in the cavity structure around the periphery of the cavity structure and wherein the detectors in the second plurality are disposed in a second C-ring configuration having an open end opposite the open end in the first C-ring configuration and wherein the second thermal neutron source is disposed in the open end of the second C-ring configuration.

15. A method as set forth in either of claims 9 or 10 wherein

the detectors are inorganic.