Hybrid radiation detection system

• US 7,636,638 B2
• Filed: 11/27/2007
• Issued: 12/22/2009
• Est. Priority Date: 11/27/2007
• Status: Expired due to Fees

• Current Assignee: Mirion Technologies Incorporated (American Capital Limited)
• Original Assignee: Canberra Industries, Inc. (American Capital Limited)
• Inventors: Morichi, Massimo, Russ, William Robert
• Primary Examiner(s): Le; John H
• Application Number:
  US11/945,851
• Publication Number:
  US 20090134337A1
• Time in Patent Office: 756 Days
• Field of Search: 702/76, 702/85, 702/22, 250/363.02, 250/370.01, 250/363, 250/370.13, 252/644
• US Class Current: 702/22
• CPC Class Codes: G01T 1/361 with a combination of detectors of different types, e.g. anti-Compton spectrometers intensity measurement with a combination of detectors G01T1/1603; with coincidence circuit G01T1/172; se provisionally also G01T1/36
• CPC Class Codes: G01V 5/20 Detecting prohibited goods, e.g. weapons, explosives, hazardous substances, contraband or smuggled objects

Abstract

A system for combining the spectral data from multiple ionizing radiation detectors of different types and having different photopeak energy resolutions. First, baseline estimation is performed on each spectral histogram separately, discerning peak regions from underlying continuum using respective peak response functions. All spectra are subsequently rebinned to the same energy calibration and the peak spectra are convolved to produce a single convolution spectrum. All peak counts are redistributed locally according to the convolution spectrum in energy regions proportional to respective local energy resolution. The summation of these redistributed peak spectra can then be analyzed as a single spectrum using a common photopeak response and energy calibration. This process can be embodied in software or firmware. A preferred hybrid system might include a combination of lower resolution, higher efficiency detectors and higher resolution, lower efficiency detectors.

Claims

1. A method for combining the individual spectral data from a plurality of ionizing radiation detectors to produce a single combined spectrum radiation analysis, the method comprising:

providing a first computing device, wherein the first computing device accepts input from a plurality of calibrated spectroscopic detectors;

detecting, using the spectroscopic detectors, the radiation level from a radioactive source;

computing spectral histograms for at least two of the spectroscopic detectors;

separating the photopeak counts from the underlying continuum counts using baseline estimation for each spectral histogram to create a respective peak spectral array;

rebinning each peak spectral array to conform to a common energy calibration;

convolving the rebinned peak spectral arrays to create a convolution array;

redistributing counts, according to the local convolution array distribution, in each rebinned spectral array over a symmetrical energy region proportional to the respective photopeak shape calibration at the channel energy;

summing the redistributed counts to obtain the combined spectrum; and

preparing a report related to the combined spectrum for display to a user.

2. The method of claim 1 wherein the rebinned spectral arrays are convolved by multiplying photopeak counts plus uncertainty in each energy bin raised to a specified power.

3. The method of claim 1 wherein the rebinned spectral arrays are convolved by multiplying channel values of amplitude weighted photopeak correlations.

4. The method of claim 1 wherein the detectors are of the same type.

5. The method of claim 1 wherein at least one of the detectors is of a different type.

6. The method of claim 1 wherein at least one of the detectors differs in efficiency and/or resolution than the other detectors.

7. A hybrid ionizing radiation detection system, the system comprising:

two or more ionizing radiation detectors, each with dedicated output conditioning circuitry; and

a processing device, wherein the processing device performs the method steps comprising;

(a) obtaining spectral histograms from two or more calibrated spectroscopic detectors;

(b) separating the photopeak counts from the underlying continuum counts using baseline estimation for each spectral histogram to create a respective peak spectral array;

(c) rebinning each peak spectral array to conform to a common energy calibration;

(d) convolving the rebinned peak spectral arrays to create a convolution array;

(e) redistributing counts, according to the local convolution array distribution, in each rebinned spectral array over a symmetrical energy region proportional to the respective photopeak shape calibration at the channel energy; and

(f) summing the redistributed counts to obtain the combined spectrum.

8. The system of claim 7 wherein the detectors are of the same type.

9. The system of claim 7 wherein at least one of the detectors is of a different type.

10. The system of claim 7 wherein at least one of the detectors differs in efficiency and/or resolution than the other detectors.

11. The system of claim 7 wherein the rebinned spectral arrays are convolved by multiplying photopeak counts plus uncertainty in each energy bin raised to a specified power.

12. The system of claim 7 wherein the rebinned spectral arrays are convolved by multiplying channel values of amplitude weighted photopeak correlations.

13. A computer readable medium embodying a computer program product, the program product comprising instructions, operable to enable a processing device to execute a procedure for combining the spectral data from a plurality of ionizing radiation detectors to produce a single combined spectrum, the program instructions comprising:

obtaining the outputs from a plurality of calibrated spectroscopic detectors positioned to detect the radiation level from a radioactive source;

computing spectral histograms for at least two of the spectroscopic detectors;

separating the photopeak counts from the underlying continuum counts using baseline estimation for each spectral histogram to create a respective peak spectral array;

rebinning each peak spectral array to conform to a common energy calibration;

convolving the rebinned peak spectral arrays to create a convolution array;

redistributing counts, according to the local convolution array distribution, in each rebinned spectral array over a symmetrical energy region proportional to the respective photopeak shape calibration at the channel energy;

summing the redistributed counts to obtain the combined spectrum and

preparing a report related to the combined spectrum for display to a user.

14. The computer readable medium of claim 13 wherein the rebinned spectral arrays are convolved by multiplying photopeak counts plus uncertainty in each energy bin raised to a specified power.

15. The computer readable medium of claim 13 wherein the rebinned spectral arrays are convolved by multiplying channel values of amplitude weighted photopeak correlations.

16. The computer readable medium of claim 13 wherein the detectors are of the same type.

17. The computer readable medium of claim 13 wherein at least one of the detectors is of a different type.

18. The computer readable medium of claim 13 wherein at least one of the detectors differs in efficiency and/or resolution than the other detectors.