Apparatus for identifying and tracking a targeted nuclear source

• US 5,109,227 A
• Filed: 08/31/1990
• Issued: 04/28/1992
• Est. Priority Date: 08/31/1990
• Status: Expired due to Fees

• Current Assignee: Wesley L. Godfrey
• Original Assignee: Wesley L. Godfrey
• Inventors: Godfrey, Wesley L.
• Primary Examiner(s): Swann, III, Glen R.
• Application Number:
  US07/575,843
• Time in Patent Office: 606 Days
• Field of Search: 340/600, 250/331.6, 250/358.1, 250/359.1, 364/516, 364/555, 364/527
• US Class Current: 340/600
• CPC Class Codes: G01V 5/281 detecting special nuclear material [SNM], e.g. Uranium-235, Uranium-233 or Plutonium-239
• CPC Class Codes: G08B 13/14 by lifting or attempted removal of hand-portable articles

Abstract

A plurality of fixed gamma ray detectors is deployed along a corridor or other path to be taken by a targeted nuclear source. Each fixed gamma ray detector and its associated electronics splits the spectrum of any gamma rays detected into two energy groups, one on either side of a predetermined and variable discrimination line along the energy base line. A plurality of paired single channel analyzers (dual channel analyzer), each pair collocated and electronically connected with a gamma ray detector, records the count of each portion of the detected gamma ray spectrum. A host computer computes the ratio between the radiation counts of the two energy groups on a recurring basis and compares the ratio taken on one reading of the detectors with the ratio taken on a previous reading of the detectors. An audible or visual alarm, connected to the computer, is produces when the ratio between the two energy groups has changed or has not met an expected value. To avoid simulation of the nuclear source, the coverage of the two energy groups together, in relation to the total spectrum of the detected gamma ray, or to each other, can be varied and the ratios between the upper and lower portions can be manipulated by changing the position of the discrimination line between the two energy groups. A series of the ratios obtained could be used collectively to identify the gamma emitting sample.

Claims

1. Apparatus for identifying and tracking a targeted nuclear source comprising:

detector means to detect any gamma rays emitted by said nuclear source and to convert readings of any gamma ray detected into electrical signals;

analyzing means, which measures the radiation count of any gamma rays detected", electronically connected to said detector means,

to split the spectrum of any gamma rays detected on either side of a predetermined and variable discrimination line into two energy groups, an upper portion and a lower portion, and

to compute and compare the ratio of the radiation count of said upper portion and the radiation count of said lower portion of said gamma ray spectrum taken on one reading of said detector means with the ratio of radiation counts between said upper portion and said lower portion taken on a previous reading of said detector means or with an expected value;

alarm means, electronically connected to said analyzing means, for indicating, in a particular reading by said detector means, when the ratio of radiation counts between said two energy groups has changed or has not met an expected value.

2. The apparatus of claim 1, wherein said detector means is a plurality of fixed gamma ray detectors, each said fixed gamma ray detector feeding into a photomultiplier, preamplifier and pulse amplifier, located along a corridor or other path to be taken by said targeted nuclear source.

3. The apparatus of claim 1, wherein said analyzing means is

a plurality of paired single channel analyzers, deployed in close association with said detector means, each said single channel analyzer having a count rate meter to determine the radiation count of said upper and lower portions of said gamma ray spectrum,

a host computer to determine the ratio of the radiation counts between said upper portion and said lower portion of said gamma ray spectrum and automatically compare said ratio:

to another ratio taken previously, or

to a library of ratios for various targeted nuclear sources,

actuating said alarm means when an unexpected ratio value is detected.

4. The apparatus of claim 1, wherein said alarm means produces an audible sound.

5. The apparatus of claim 1, wherein said alarm means produces a visual signal.

6. The apparatus of claim 1, wherein said alarm means produces a radio frequency signal.

7. The apparatus of claim 1, wherein said alarm means produces an infrared signal.

8. The apparatus of claim 1, wherein said two energy groups together exactly cover the spectrum of said detected gamma rays without overlapping each other.

9. The apparatus of claim 1, wherein said two energy groups do not entirely cover the spectrum of said detected gamma rays.

10. The apparatus of claim 1, wherein said two energy groups overlap in whole or in part.

11. The apparatus of claim 1, wherein the ratio of said two energy groups is the same for each said fixed gamma ray detector.

12. The apparatus of claim 1, wherein the ratio of said two energy groups is not the same for each said fixed gamma ray detector.

13. The apparatus of claim 1, wherein the series of ratios between said two energy groups obtained is used collectively to identify said targeted nuclear source.

14. The apparatus of claim 1, wherein said alarm means is actuated if the series of ratios between said two energy groups does not match a series of corresponding ratios from a known sample of a targeted nuclear source.