Detection of buried nitrogen rich materials

• US 5,410,575 A
• Filed: 01/27/1993
• Issued: 04/25/1995
• Est. Priority Date: 01/27/1993
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Uhm, Han S.
• Primary Examiner(s): BEHREND, HARVEY E
• Application Number:
  US08/010,036
• Time in Patent Office: 818 Days
• Field of Search: 376/159, 376/160, 376/161, 89/1.13, 102/402, 342/459
• 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

Fast neutrons from a moving source are thermalized by travel through water to a soil embedded body of nitrogen-rich material causing emission of gamma rays therefrom. Emitted gamma rays are detected at a location adjacent the neutron source for measurement of radiation energy from which location of nitrogen-rich materials in the soil is mapped, based on a predetermined signature energy level of the measured radiation.

Claims

1. In a method of sensing nitrogen-rich explosives within an embedding medium by capture therein of neutrons emitted from a continuously moving source in spaced relation to said explosive, causing emission therefrom of-gamma rays, the steps of:

thermalizing said emitted neutrons prior to reaching the nitrogen-rich explosives by penetration of said embedding medium;

detecting said gamma rays in spaced adjacency to the continuously moving source; and

tracking the nitrogen-rich explosives in response to measurement of the detected gamma rays above a predetermined signature energy level corresponding to said explosives.

2. The method of claim 1 wherein said step of thermalizing the emitted neutrons comprises location of the continuously moving neutron source within water as a hydrogen-rich surrounding medium different from said embedding medium.

3. The method of claim 2 wherein said embedding medium is underwater soil.

4. The method of claim 1 wherein said embedding medium is underwater soil.

5. The method of claim 4 wherein said neutrons are emitted from the moving source at an energy level of substantially 14 MeV and a flux density of 10¹¹ neutrons per second while the predetermined signature energy level of the detected gamma rays is 8 MeV.

6. The method of claim 1 wherein said neutrons are emitted from the moving source at an energy level of substantially 2 MeV and a flux density of 10¹⁰ neutrons per second while the predetermined signature energy level of the detected gamma rays is 8 MeV.

7. In a method of sensing nitrogen-rich materials buried in soil and water by capture of neutrons causing emission of gamma rays therefrom, the steps of:

emitting said neutrons from a source during movement within the water in spaced relation to the soil and at a predetermined energy level enabling sequential penetration of the soil and the nitrogen-rich materials after thermalization by the water;

detecting said gamma rays in spaced adjacency to said source; and

measuring energy level of the detected gamma rays above a predetermined energy signature to map location of the nitrogen-rich materials during said movement of the source.

8. The method of claim 7 wherein said soil is a sea bed located below the water.

9. The method of claim 7 wherein said soil and water form an earth mixture.

10. The method of claim 8 wherein said predetermined energy signature level is 8 meV.

11. The method of claim 10 wherein said nitrogen-rich materials are explosives of underwater mines.