Method and system for calibrating gamma radiation flux levels in a solid state gamma radiation detection system

• US 10,234,576 B2
• Filed: 04/29/2016
• Issued: 03/19/2019
• Est. Priority Date: 04/30/2015
• Status: Active Grant

• Current Assignee: Ludlum Measurements, Inc.
• Original Assignee: VPI Engineering, Inc.
• Inventors: Marriott, Kevin, Hepworth, Paul, Williams, Jeremy
• Primary Examiner(s): Porta, David P
• Assistant Examiner(s): Valentiner, Jeremy S
• Application Number:
  US15/143,205
• Publication Number:
  US 20160320501A1
• Time in Patent Office: 1,054 Days
• CPC Class Codes: G01T 1/40 Stabilisation of spectrometers
• CPC Class Codes: G01T 7/005 calibration techniques stabilization of spectrometer G01T1/40

Abstract

One aspect of the present disclosure comprises a method for calibrating a drive level of a non-radioactive calibration source. Another aspect of the present disclosure comprises a method for using a non-radioactive calibration source to verify correct operation of a radiation detector. Another aspect of the present disclosure comprises a radiation detection system that comprises a radiation detector and a non-radioactive calibration source that is used to verify correct operation of the radiation detector.

Claims

1. A method for calibrating a drive level of a non-radioactive calibration source, comprising:

measuring a response of a radiation detector to background radiation, wherein the background radiation has a known, stable level, the known, stable level of background radiation being known through a field measurement or relative check;

measuring a response of the radiation detector to the background radiation plus a radiation reference, wherein the radiation reference is a radiation source with known properties located at a specific distance from the radiation detector to provide a known reference dose rate above the background radiation;

measuring a response of the radiation detector to the background radiation plus the non-radioactive calibration source; and

adjusting the drive level of the non-radioactive calibration source until the response of the radiation detector to the background radiation plus the non-radioactive calibration source substantially matches the response of the radiation detector to the background radiation plus the radiation reference.

2. The method of claim 1, wherein the non-radioactive calibration source comprises a light-emitting diode (LED).

3. The method of claim 1, wherein:

the radiation reference is not within range of the radiation detector and the non-radioactive calibration source is off when the response of the radiation detector to the background radiation is measured;

the non-radioactive calibration source is off when the response of the radiation detector to the background radiation plus the radiation reference is measured; and

the radiation reference is not within range of the radiation detector when the response of the radiation detector to the background radiation plus the non-radioactive calibration source is measured.

4. The method of claim 1, further comprising storing verification data comprising the drive level of the non-radioactive calibration source that caused the response of the radiation detector to the background radiation plus the non-radioactive calibration source to substantially match the response of the radiation detector to the background radiation plus the radiation reference.

5. The method of claim 4, wherein the verification data further comprises at least one of:

the response of the radiation detector to the background radiation;

the response of the radiation detector to the background radiation plus the non-radioactive calibration source;

a difference between the response of the radiation detector to the background radiation plus the non-radioactive calibration source and the response of the radiation detector to the background radiation;

a known dose rate of the radiation reference; and

a temperature of at least one of the radiation detector and the non-radioactive calibration source when the response of the radiation detector to the background radiation plus the non-radioactive calibration source is measured.

6. The method of claim 1, further comprising:

measuring at least one temperature corresponding to at least one of the radiation detector and the non-radioactive calibration source when the response of the radiation detector to the background radiation is measured;

measuring at least one temperature corresponding to at least one of the radiation detector and the non-radioactive calibration source when the response of the radiation detector to the background radiation plus the radiation reference is measured; and

measuring at least one temperature corresponding to at least one of the radiation detector and the non-radioactive calibration source when the response of the radiation detector to the background radiation plus the non-radioactive calibration source is measured.

7. The method of claim 6, further comprising restarting calibration if the at least one temperature that is measured when the response of the radiation detector to the background radiation plus the non-radioactive calibration source is measured does not substantially match:

the at least one temperature that is measured when the response of the radiation detector to the background radiation is measured; and

the at least one temperature that is measured when the response of the radiation detector to the background radiation plus the radiation reference is measured.

8. The method of claim 1, further comprising repeating the steps of measuring the response of the radiation detector to the background radiation plus the radiation reference, measuring the response of the radiator detector to the background radiation plus the non-radioactive calibration source, and adjusting the drive level of the non-radioactive calibration source for at least one additional radiation reference.

9. The method of claim 1, further comprising:

configuring a thermoelectric cooling system to maintain a new temperature for at least one of the radiation detector and the non-radioactive calibration source; and

repeating the steps of measuring the response of the radiation detector to the background radiation, measuring the response of the radiation detector to the background radiation plus the radiation reference, measuring the response of the radiation detector to the background radiation plus the non-radioactive calibration source, and adjusting the drive level of the non-radioactive calibration source while maintaining the new temperature.

10. A method for verifying calibration of a radiation detector, comprising:

measuring a response of the radiation detector to background radiation;

driving a non-radioactive calibration source to a drive level that is specified in verification data, the verification data being determined during calibration of the non-radioactive calibration source, wherein calibration of the non-radioactive calibration source comprises adjusting a calibration drive level of the non-radioactive calibration source until a response of the radiation detector to a calibration background radiation plus the non-radioactive calibration source substantially matches a response of the radiation detector to the calibration background radiation plus a radiation reference, wherein the calibration background radiation has a known, stable level, the known, stable level of background radiation being known through a field measurement or relative check, and wherein the radiation reference is a radiation source with known properties located at a specific distance from the radiation detector to provide a known reference dose rate above the calibration background radiation;

measuring a response of the radiation detector to the background radiation plus the non-radioactive calibration source; and

determining whether the radiation detector is calibrated based on the verification data and the response of the radiation detector to the background radiation plus the non-radioactive calibration source.

11. The method of claim 10, further comprising determining that the radiation detector is calibrated if a difference between the response of the radiation detector to the background radiation plus the non-radioactive calibration source and the response of the radiation detector to the background radiation substantially matches a corresponding value in the verification data.

12. The method of claim 10, further comprising determining that the radiation detector is not calibrated if a difference between the response of the radiation detector to the background radiation plus the non-radioactive calibration source and the response of the radiation detector to the background radiation does not substantially match a corresponding value in the verification data.

13. The method of claim 10, wherein:

the non-radioactive calibration source is off when the response of the radiation detector to the background radiation is measured; and

the method is performed without any radiation sources other than the background radiation within range of the radiation detector.

14. The method of claim 10, further comprising:

measuring at least one temperature corresponding to at least one of the radiation detector and the non-radioactive calibration source when the response of the radiation detector to the background radiation is measured; and

measuring at least one temperature corresponding to at least one of the radiation detector and the non-radioactive calibration source when the response of the radiation detector to the background radiation plus the non-radioactive calibration source is measured.

15. The method of claim 10, wherein the verification data comprises data corresponding to a plurality of different radiation references, and further comprising:

identifying a subset of the verification data corresponding to a radiation reference dose rate that is closest to a dose rate of interest; and

using the subset of the verification data to determine whether the radiation detector is operating correctly.

16. The method of claim 10, wherein the verification data comprises data corresponding to a plurality of different temperature points, and further comprising:

identifying a subset of the verification data corresponding to a temperature point that is closest to a current measured temperature; and

using the subset of the verification data to determine whether the radiation detector is operating correctly.

17. A radiation detection system, comprising:

a radiation detector;

a non-radioactive calibration source, wherein the radiation detector and the non-radioactive calibration source are positioned such that photons emitted from the non-radioactive calibration source are detected by the radiation detector;

memory for storing verification data, wherein verification data comprises a drive level of the non-radioactive calibration source determined by adjusting the drive level of the non-radioactive calibration source until a response of the radiation detector to a background radiation plus the non-radioactive calibration source substantially matches a response of the radiation detector to the background radiation plus a radiation reference, wherein the background radiation has a known, stable level, the known, stable level of background radiation being known through a field measurement or relative check, and wherein the radiation reference is a radiation source with known properties located at a specific distance from the radiation detector to provide a known reference dose rate above the background radiation; and

a light shield that shields the radiation detector from outside light sources.

18. The radiation detection system of claim 17, further comprising a thermoelectric cooling system that controls a temperature of the radiation detector.

19. The radiation detection system of claim 17, further comprising a thermoelectric cooling system that controls a temperature of the non-radioactive calibration source.

20. The radiation detection system of claim 17, further comprising a printed circuit board (PCB), wherein:

the radiation detector and the non-radioactive calibration source are mounted to the PCB; and

the light shield is attached to the PCB such that the light shield covers the radiation detector and the non-radioactive calibration source, and a light-tight seal exists between the light shield and the PCB.