Use of spectral information to extend temperature range of gamma-ray detector

Patent metadata

Field	Value
Publication number	US-9329302-B2
Application number	US-201213629268-A
Country	US
Kind code	B2
Filing date	Sep 27, 2012
Priority date	Sep 27, 2012
Publication date	May 3, 2016
Grant date	May 3, 2016

Abstract

A method is for detecting gamma rays using a gamma ray detector, and includes determining a first count of gamma rays having an energy in a first energy interval, using a controller coupled to the gamma ray detector. A second count of gamma rays having an energy in a second energy interval is determined, the second energy interval having a higher energy than the first energy interval, using the controller. A third count of gamma rays having an energy in a third energy interval is determined, the third energy interval having a higher energy than the second energy interval, using the controller. The second count of gamma rays is compensated for noise based upon a ratio of the second count and the third count, using the controller.

First claim

The invention claimed is:

1. A method of detecting gamma rays using a gamma ray detector comprising:
determining a first count of gamma rays having an energy in a first energy interval, using a controller coupled to the gamma ray detector;
determining a second count of gamma rays having an energy in a second energy interval, the second energy interval having a higher energy than the first energy interval, using the controller;
determining a third count of gamma rays having an energy in a third energy interval, the third energy interval having a higher energy than the second energy interval, using the controller;
compensating the second count of gamma rays for noise based upon a ratio of the second count and the third count, using the controller;
adjusting a system gain of the gamma ray detection system such that the ratio of the second count and the third count is constant in an absence of noise in the first energy interval; and
detecting noise in the first energy interval based upon a ratio of the first count to the second count exceeding a given ratio, and ceasing system gain adjustment based thereupon.

2. A method as in claim 1 , wherein the gamma ray detector is configured to detect a gamma ray spectrum; wherein the gamma ray spectrum has a backscatter peak; and wherein the second and third intervals are on opposite sides of the backscatter peak.

3. A method as in claim 1 , further comprising adjusting the system gain so as to match the ratio of the second count and the third count to a borehole environment.

4. A method as in claim 1 , further comprising decreasing the system gain after ceasing the system gain adjustment based upon detecting the noise in the first energy interval.

5. A method as in claim 1 , further comprising resuming system gain adjustment based upon the ratio of the first count to the second count falling below a given ratio.

6. A method as in claim 1 , wherein the first, second, and third energy intervals are contiguous.

7. A method as in claim 1 , wherein the first, second, and third energy intervals are not contiguous.

8. A method as in claim 1 , wherein the noise comprises temperature induced noise.

9. A method as in claim 1 , wherein the noises comprises shock induced noise.

10. A method of measuring a spectrum of gamma rays in a borehole comprising:
detecting a gamma ray spectrum using a gamma ray detector positioned in the borehole;
determining a first count of gamma rays having an energy in a first energy interval, using a controller coupled to the gamma ray detector;
determining a second count of gamma rays having an energy in a second energy interval, the second energy interval having a higher energy than the first energy interval, using the controller;
determining a third count of gamma rays having an energy in a third energy interval, the third energy interval having a higher energy than the second energy interval, using the controller;
adjusting a system gain such that a ratio of the second count and the third count is constant in an absence of noise in the first energy interval; and
detecting noise in the first energy interval based upon a ratio of the first count to the second count exceeding a given ratio, and ceasing system gain adjustment based thereupon.

11. A method as in claim 10 , further comprising decreasing the system gain after ceasing the system gain adjustment based upon detecting the noise in the first energy interval.

12. A method as in claim 10 , further comprising resuming system gain adjustment based upon the ratio of the first count to the second count falling below a given ratio.

13. A method as in claim 10 , further comprising compensating the second count of gamma rays for the noise based upon the known ratio of the second count and the third count as

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14. A method as in claim 7 , wherein the gamma ray spectrum has a backscatter peak;
and wherein the second and third intervals are on opposite sides of the backscatter peak.

15. A method of detecting gamma rays using a gamma ray detector comprising:
determining an absence of noise in a first energy interval, using a controller coupled to the gamma ray detector;
in the absence of noise in the first energy interval, determining a second noise free count of gamma rays having an energy in a second energy interval, the second energy interval having a higher energy than the first energy interval, using the controller;
in the absence of noise in the first energy interval, determining a third noise free count of gamma rays having an energy in a third energy interval, the third energy interval having a higher energy than the second energy interval, using the controller;
determining a presence of noise in the first energy interval, using the controller;
in the presence of noise in the first energy interval, determining a second count of gamma rays having an energy in the second energy interval, using the controller;
in the presence of noise in the first energy interval, determining a third count of gamma rays having an energy in the third energy interval, using the controller; and
compensating the second count for noise in the second energy interval based upon a ratio of the second noise free count to the third noise free count, and based upon the third count obtained in the presence of noise.

16. A method as in claim 15 , further comprising adjusting a system gain via a gain regulation scheme not based upon a ratio of the second noise free count to the third noise free count, and not based upon a ratio of the second count to the third count.

17. A method as in claim 15 , wherein the absence of noise in the first energy interval is determined by determining a first count of gamma rays having an energy in the first energy interval, determining a second count of gamma rays having an energy in the second energy interval, and determining that the ratio of the first count to the second count does not exceed a given ratio.

18. A method as in claim 15 , wherein the presence of noise in the first energy interval is determined by determining a first count of gamma rays having an energy in the first energy interval, determining a second count of gamma rays having an energy in the second energy interval, and determining that the ratio of the first count to the second count exceeds a given ratio.

19. A radiation detection system comprising:
a radiation detector;
a controller coupled to the radiation detector and configured to
determine a first count of radiation having an energy in a first energy interval,
determine a second count of radiation having an energy in a second energy interval, the second energy interval having a higher energy than the first energy interval,
determine a third count of radiation having an energy in a third energy interval, the third energy interval having a higher energy than the second energy interval, and
compensate the second count o

Assignees

• Stoller Christian
• Schlumberger Technology Corp

Inventors

• Stoller Christian

Classifications

• G01T1/20 Primary

  with scintillation detectors · CPC title

• G01T1/362

  with scintillation detectors · CPC title

• G01V5/06 Primary

  for detecting naturally radioactive minerals · CPC title

• G01V5/04

  specially adapted for well-logging · CPC title