Correction of a radioactivity measurement using particles from atmospheric source

• US 8,275,567 B2
• Filed: 03/21/2007
• Issued: 09/25/2012
• Est. Priority Date: 03/22/2006
• Status: Active Grant

• Current Assignee: Cavendish Nuclear (Overseas) Ltd. (Babcock International Group PLC)
• Original Assignee: VT Nuclear Services Limited
• Inventors: Lightfoot, John
• Primary Examiner(s): Le, Toan M
• Application Number:
  US12/281,970
• Publication Number:
  US 20100010764A1
• Time in Patent Office: 2,015 Days
• Field of Search: 702/104, 702/1, 702/23, 702 26- 32, 702/81, 702 84- 85, 702/101, 702127-129, 702/137, 702173-174, 702181-183, 702188-190, 250/251, 250/301, 250305-308, 250/332, 250/334, 25037008-37011, 250/390.02, 250/390.04, 250/390.06, 250/390.11, 250/393, 250/396.R, 250/397, 250/492.1, 250/492.3, 250/580, 250/591
• US Class Current: 702/104
• CPC Class Codes: G01T 1/167 Measuring radioactive content of objects, e.g. contamination whole body counters G01T1/163
• CPC Class Codes: G01V 5/22 Active interrogation, i.e. by irradiating objects or goods using external radiation sources, e.g. using gamma rays or cosmic rays
• CPC Class Codes: G01V 5/26 Passive interrogation, i.e. by measuring radiation emitted by objects or goods

Abstract

A method of correcting a measure of radioactive material within a body of material includes measuring a characteristic of the radioactive material to provide a measure, such as gamma emissions; detecting muons and/or electrons generated by muons which have not passed through the body of material to give a first value; detecting muons and/or electrons generated by muons which have passed through the body of material to give a second value; processing the first value and second value to give a factor, for instance indicative of the density of the body of material; and correcting the measure using the factor to obtain a corrected measure of the radioactive material with the body of material, for instance to correct for the density of the body of material and attendant issues such as attenuation and shielding.

Claims

1. A method of determining an amount of radioactive material within a body of material, the method comprising:

determining a preliminary measure of an amount of radioactive material within a body of material by directly and/or indirectly measuring emissions generated by the radioactive material;

detecting muons and/or electrons generated by muons which have not passed through the body of material to give a first value;

detecting muons and/or electrons generated by muons which have passed through the body of material to give a second value;

processing the first value and second value to determine a factor, the factor being an expression of density and being a function of the second value divided by a product of a calibration factor and the first value; and

applying the factor to the preliminary measure of the amount of radioactive material within the body of material to obtain a corrected measure of the amount of radioactive material within the body of material.

2. A method according to claim 1 in which the preliminary measure of the radioactive material within a body of material is corrected for density.

3. A method according to claim 1 in which the preliminary measure of the radioactive material within a body of material is corrected differently for different parts of the body of material.

4. A method according to claim 1 in which the method further comprises determining the weight and/or mass of a container and its body of material or the weight or mass of the body of material to provide a determined weight.

5. A method according to claim 4 in which a calculated mass or weight for the body of material and/or the container and body of material is obtained and the calculated mass or weight is compared with the determined mass or weight.

6. A method according to claim 5 in which one or more expressions of areal density or areal densities are adjusted if the calculated weight or mass is different from the determined weight or mass.

7. A method according to claim 6 in which the adjusted expression of areal density or adjusted areal density is used in determining the factor.

8. A method according to claim 5 in which one or more expressions of areal density or areal density are normalised based upon the calculated weight or mass compared with the determined weight or mass.

9. A method according to claim 1 in which the muons and/or electrons contributing to the first value and second value provide a coincidence count value, and the ratio of the coincidence count value to the first value is considered in the calculation of the factor.

10. A method according to claim 9 in which the first value is corrected before being used.

11. A method according to claim 10 in which the first value is corrected for the effect of geometry in respect of a pair of first and second detectors and/or a pair of first and third detectors used to obtain the second value.

12. A method according to claim 10 in which a separate correction is provided for each first value, with the correction being specific to the pair of first and second detectors giving the second value and/or the pair of first and third detectors giving the second value.

13. A method according to claim 9 in which the ratio of the coincidence count value to the first value is used to account for the effect of the body of material and/or container and body of material on particles passing through the second detector and on a path which would have taken them through the first detector if the body of material and/or container and body of material were absent.

14. A method according to claim 9 in which the ratio of the coincidence count value to the first value is used to account for the effect of the body of material and/or container and body of material on particles passing through the first detector and on a path which would have taken them through the third detector if the body of material and/or container and body of material were absent.

15. A method according to claim 9 in which the ratio of the coincidence count value to the first value is used to calculate an expression of areal density or an areal density for the body of material or segment thereof.

16. A method according to claim 9 in which two or more first detectors and/or two or more second detectors and/or two or more third detectors are provided and the ratio of the coincidence count value to the first value is considered for two or more different pairs of detectors.

17. A method according to claim 16 in which a pair of detectors is formed of a first and third detector or first and second detector.

18. A method according to claim 16 in which a calculation of an expression of areal density or of an areal density is provided for two or more pairs of detectors.

19. A method according to claim 1 in which a plurality of expressions of areal density or a plurality of areal densities are obtained for the body of material or for segments thereof.

20. A method according to claim 19 in which, where a plurality of expressions of areal density or a plurality of areal densities are obtained, those expressions or densities are combined to give a combined areal density expression or combined areal density.

21. A method according to claim 20 in which a weighted combination of two or more expressions of areal density or of areal densities is provided.

22. A method according to claim 1 in which an expression of areal density or an areal density is used to calculate a calculated mass or weight for the body of material and/or the container and body of material.

23. A method according to claim 1 in which corrected measure is greater than the preliminary measure.

24. A method according to claim 1 in which the first value is obtained from one or more first detectors provided below a measuring location at which the body of material is provided when the preliminary measure of radioactive material within the body of material is made, the first value being obtained with the body of material absent.

25. A method according to claim 24 in which the second value is obtained from one or more first detectors provided below a measuring location at which the body of material is provided when the preliminary measure of radioactive material within the body of material is made, the second value being obtained with the body of material present.

26. A method according to claim 25 in which the ratio or reciprocal ratio of the second value to the first value provides an indication or measure of the density for the body of material.

27. A method according to claim 1 in which the first value is obtained from one or more second detectors provided above a measuring location at which the body of material is provided when the preliminary measure of radioactive material within the body of material is made.

28. A method according to claim 1 in which the second value is obtained from one or more first detectors provided below a measuring location at which the body of material is provided when the preliminary measure of radioactive material within the body of material is made, the second value being obtained with the body of material present.

29. A method according to claim 28 in which the ratio or reciprocal ratio of the coincidence count value observed in the first value and second value, to the first value provides an indication or measure of the density for the body of material.

30. A method according to claim 28 in which the second value is obtained from one or more first detectors together with one or more third detectors.

31. A method according to claim 30 in which the ratio or reciprocal ratio of the coincidence count value obtained from the first detectors and third detectors to the first value provides an indication or measure of the density for the body of material.

32. A method according to claim 1 in which all of the detectors are provided within 2 m of the edge of the measuring location and/or a part of a container for the body of material and/or the body of material.

33. A method according to claim 1, wherein the preliminary and corrected measures of the amount of radioactive material within the body of material is expressed as one or more from the group including:

a count, a count rate, an activity level, and a mass equivalent value.

34. Apparatus for determining an amount of radioactive material within a body of material, the apparatus comprising:

one or more detectors that measure a characteristic of radioactive material, the one or more detectors providing a preliminary measure of the amount of radioactive material within a body of material by directly and/or indirectly measuring emissions generated by the radioactive material;

one or more first detectors positioned above a measuring location, the one or more first detectors detecting one or more types of particle from an atmospheric source which have not passed through the body of material to give a first value;

one or more second detectors positioned below a measuring location, the one or more second detectors detecting one or more types of particle from an atmospheric source which have passed through the body of material to give a second value;

a processor for processing the first value and second value to give a factor, wherein the factor is an expression of density and wherein the factor is a function of the second value divided by a product of a calibration factor and the first value, the processor further applying the factor to preliminary measure of the amount of radioactive material within the body of material to obtain a corrected measure of the amount of radioactive material within the body of material.

35. A method of determining an amount of radioactive material within a body of material, the method comprising:

determining a preliminary measure of an amount of radioactive material within a body of material by directly and/or indirectly measuring emissions generated by the radioactive material;

using a second detector to detect one or more types of particle from an atmospheric source which have not passed through the body of material to give a first value;

using a first detector to detect one or more types of particle from an atmospheric source which have passed through the second detector and the body of material to give a second value;

processing the first value and second value to give a factor, the factor being an expression of density and being a function of the second value divided by a product of a calibration factor and the first value; and

applying the factor to the preliminary measure of the amount of radioactive material within the body of material to obtain a corrected measure of the amount of radioactive material with the body of material.

36. A method of establishing an error in a factor, the factor being used in a method of correcting a measure of radioactive material within a body of material, the method comprising:

determining a preliminary measure of an amount of radioactive material within a body of material by directly and/or indirectly measuring emissions generated by the radioactive material;

using a second detector to detect one or more types of particle from an atmospheric source which have not passed through the body of material to give a first value;

using a first detector to detect one or more types of particle from an atmospheric source which have passed through the second detector and the body of material to give a second value;

processing the first value and second value to give the factor, the factor being an expression of density and being a function of the second value divided by a product of a calibration factor and the first value;

applying the factor to the preliminary measure of the amount of radioactive material within the body of material to obtain a corrected measure of the amount of radioactive material with the body of material; and

determining the error in the factor by;

considering the first value as being accurately measured, considering the calibration factor as being accurately known and considering the second value as being the first value multiplied by a probability, the probability being that of a particle contributing to the first value and to the second value.