Validation and calibration apparatus and method for nuclear density gauges

• US 5,923,726 A
• Filed: 06/12/1997
• Issued: 07/13/1999
• Est. Priority Date: 06/12/1997
• Status: Expired due to Term

• Current Assignee: InstroTek, Inc.
• Original Assignee: InstroTek, Inc.
• Inventors: Regimand, Ali
• Primary Examiner(s): Porta, David P.
• Application Number:
  US08/873,815
• Time in Patent Office: 761 Days
• Field of Search: 378/53, 378/54, 378/56, 378/86, 378/88, 378/89, 378/90, 378/207, 250/252.1, 250/390.01, 250/390.04
• US Class Current: 378/207
• CPC Class Codes: G01N 23/06 and measuring the absorption

Abstract

A cost effective, field-usable validation and calibration apparatus and method for nuclear density gauges comprises an absorption element, where absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge. The absorption element may be positioned inside an enclosure, which also may include an insertion hole capable of receiving a source rod from a nuclear density gauge. The absorption element also can be capable of simulating a plurality of densities, both in backscatter and direct transmission modes. A method of validating and re-calibrating a nuclear density test gauge is also provided, where only a single block of a known density, either a reference block or a field block with a simulated density, is required.

Claims

1. A field block for use with a nuclear density gauge comprising an absorption element, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, said field block further comprising an enclosure, said absorption element being positioned inside said enclosure, and wherein said enclosure comprises a material having a density sufficient to substantially block radiation generated by the nuclear density gauge from exiting said enclosure.

2. A field block for use with a nuclear density gauge comprising an absorption element, wherein said absorbtion element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field block further comprises an insertion tube positioned within said enclosure and capable of receiving the source rod for the purpose of conducting direct transmission nuclear density readings, and wherein said absorption element is positioned on said insertion tube.

3. A field block for use with a nuclear density gauge comprising an absorption element, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein said absorption element is capable of simulating a plurality of different densities when subjected to testing by the nuclear density gauge.

4. A field block for use with a nuclear density gauge comprising an absorption element, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, said field block further comprising an enclosure, said absorption element being positioned inside said enclosure, and wherein said absorption element has a plurality of positions within said enclosure, and the nuclear density gauge will perceive a corresponding plurality of simulated density readings, when said absorption element is placed in said plurality of positions.

5. A field block for use with a nuclear density gauge comprising an absorption element, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field block further comprises an insertion tube positioned within said enclosure and capable of receiving the source rod for the purpose of conducting direct transmission nuclear density readings, wherein said insertion tube has a depth allowing the source rod of the nuclear density gauge to take a plurality of readings at increments along the depth, and wherein said absorption element substantially simulates at least one desired density at each of the plurality of depth positions.

6. A field block for use with a nuclear density gauge comprising an absorption element, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, and wherein said absorption element is lead.

7. A field block for use with a nuclear density gauge comprising an absorption element, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field block further comprises an insertion tube positioned within said enclosure and capable of receiving the source rod for the purpose of conducting direct transmission nuclear density readings, wherein said absorption element increases in thickness as the depth of the insertion tube increases.

8. A field block for use with a nuclear density gauge comprising an absorption element, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field block further comprises an insertion tube positioned within said enclosure and capable of receiving the source rod for the purpose of conducting direct transmission nuclear density readings, and wherein said absorption element increases in thickness radially from said insertion tube.

9. The field block of claim 8 where the absorption element is rotatably mounted within the enclosure.

10. The field block of claim 8 where the absorption element has the same shape along the length of the insertion tube.

11. A method of constructing a field block for use with a nuclear density gauge comprising:

a. providing an absorption element;

b. taking a reading using the absorption element with a calibrated nuclear density gauge to determine if the field block simulates a desired density;

c. if necessary, altering the composition or configuration of the absorption element and retaking the reading with the nuclear test gauge until the gauge gives a density reading substantially the same as the desired density.

12. The method of claim 11, further comprising providing an enclosure for the absorption element, wherein said enclosure is lined with a photon absorbing material.

13. A method of validating the calibration of a nuclear density gauge, which is capable of determining densities at incremental depths, comprising:

a. providing a block with known densities per incremental depth;

b. providing a nuclear density gauge;

c. taking counts and density readings of the block using the nuclear gauge;

d. validating the calibration of the gauge by comparing the nuclear density gauge readings with the known densities per incremental depth.

14. The method of claim 13 where the block with a known density is a field block comprising an absorption element which simulates a known density.

15. A method of validating a nuclear density gauge at multiple desired densities, where the gauge has an existing calibration and related constants, comprising:

a. selecting a plurality of desired densities;

b. providing a nuclear density gauge with the ability to take readings incrementally at a plurality of source rod depths;

c. providing a block with a known density;

d. obtaining counts on the block with a known density;

e. calculating counts at each selected desired density at each incremental depth, using the gauge'"'"'s existing calibration constants;

f. correcting all counts for decay;

g. correcting all counts for electronic and mechanical changes in the gauge;

h. calculate densities for all corrected counts at all incremental depths;

i. validate gauge by comparing calculated densities with selected desired densities.

16. The method of claim 15, wherein said block with a known density is a field instrument comprising an absorption element which simulates a known density.

17. The method of claim 15 wherein said block with a known density is a reference block of known density and composition.

18. A method of re-calibrating a nuclear density gauge comprising

a. selecting a plurality of desired densities;

b. providing a nuclear density gauge with the ability to take readings incrementally at a plurality of source rod depths;

c. providing a block with a known density;

d. obtaining counts on the block with a known density;

e. calculating counts at each selected desired density at each incremental depth, using the gauge'"'"'s existing calibration constants;

f. correcting all counts for decay;

g. correcting all counts for electronic and mechanical changes in the gauge;

h. calculate count ratio by dividing calculated counts by a daily standard count taken on reference block provided with gauge;

i. re-calibrating the gauge by determining constants A, B and C at each depth according to following equation at each depth using a curve-fitting method

space="preserve" listing-type="equation">CR=A e.sup.(-BD) -C

where CR is a ratio of the count on the block of known density and the daily standard count;

A, B and C are gauge parameters for each depth; and

D is the material density.

19. The method of claim 18 where the block with a known density is a field block comprising an absorption element which simulates the known density.

20. The method of claim 18, wherein said block with a known density is a reference block of known density and composition.

21. A method of validating a nuclear density gauge at multiple desired densities, where the gauge has an existing calibration and related constants, comprising:

a. selecting a plurality of desired densities;

b. providing a nuclear density gauge;

c. providing a block with a known density;

d. obtaining counts on the block with a known density;

e. calculating counts at each selected desired density, using the gauge'"'"'s existing calibration constants;

f. correcting all counts for decay;

g. correcting all counts for electronic and mechanical changes in the gauge;

h. calculate densities for all corrected counts;

i. validate gauge by comparing calculated densities with selected desired densities.

22. A method of re-calibrating a nuclear density gauge comprising

a. selecting a plurality of desired densities;

b. providing a nuclear density gauge;

c. providing a block with a known density;

d. obtaining counts on the block with a known density;

e. calculating counts at each selected desired density, using the gauge'"'"'s existing calibration constants;

f. correcting all counts for decay;

g. correcting all counts for electronic and mechanical changes in the gauge;

h. calculate count ratio by dividing calculated counts by a daily standard count taken on reference block provided with gauge;

i. re-calibrating the gauge by determining constants A, B and C according to the following equation at each depth using a curve-fitting method

space="preserve" listing-type="equation">CR=A e.sup.(-BD) -C

where CR is a ratio of the count on the block of known density and the daily standard count;

A, B and Care gauge calibration constants, and D is the material density.

23. The method of claim 22 where the block with a known density is a field block comprising an absorption element which simulates the known density.

24. The method of claim 22, wherein said block with a known density is a reference block of known density and composition.

25. A field-useable instrument for use with a nuclear density gauge comprising an absorption element and an enclosure for holding said absorption element therein, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, and wherein said enclosure is configured to substantially block radiation emitted by the nuclear density gauge from exiting said enclosure.

26. An instrument for use with a nuclear density gauge comprising an absorption element, wherein said absorption element is capable of simulating a plurality of different densities when subjected to analysis using the nuclear density gauge.

27. A field useable instrument for use with a nuclear density gauge comprising an absorption element and an enclosure for holding said absorption element therein wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field instrument further comprises an insertion tube positioned within said enclosure configured to receive the source rod for the purpose of conducting direct transmission nuclear density readings, and wherein said absorption element is translatable into a plurality of positions within said enclosure, and wherein the nuclear density gauge will perceive a corresponding plurality of simulated density readings when said absorption element is placed in said plurality of positions.

28. A field useable instrument for use with a nuclear density gauge comprising an absorption element and an enclosure for holding said absorption element therein wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field instrument further comprises an insertion tube positioned within said enclosure configured to receive the source rod for the purpose of conducting direct transmission nuclear density readings, and wherein said absorption element is positioned on said insertion tube, and wherein said insertion tube has a longitudinal depth allowing the source rod of the nuclear density gauge to generate a plurality of readings at increments along said longitudinal depth, and wherein said absorption element simulates at least one density at each of said increment depth positions.

29. A field useable instrument for use with a nuclear density gauge comprising an absorption element and an enclosure for holding said absorption element therein, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field instrument further comprises an insertion tube positioned within said enclosure configured to receive the source rod for the purpose of conducting direct transmission nuclear density readings, and wherein said absorption element increases in thickness along the longitudinal depth of said insertion tube.

30. A field useable instrument for use with a nuclear density gauge comprising an absorption element and an enclosure for holding said absorption element therein, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field instrument further comprises an insertion tube positioned within said enclosure configured to receive the source rod for the purpose of conducting direct transmission nuclear density readings, and wherein said absorption element has a radial thickness and an associated longitudinal length extending between the top and bottom of said absorption element, and wherein said radial thickness increases along said longitudinal length.

31. The field-useable instrument of claim 30, wherein said absorption element is moveable within said enclosure.

32. A field useable instrument for use with a nuclear density gauge comprising an absorption element and an enclosure for holding said absorption element therein, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, wherein the nuclear density gauge comprises a source rod and a detector and the field instrument further comprises an insertion tube positioned within said enclosure configured to receive the source rod for the purpose of conducting direct transmission nuclear density readings, and wherein said absorption element comprises at least two different materials, a first material and a second material, and wherein said first material is a high density material.

33. A field useable instrument for use with a nuclear density gauge comprising an absorption element and an enclosure for holding said absorption element therein, wherein said absorption element is capable of simulating at least one known density when subjected to analysis using the nuclear density gauge, and wherein the nuclear density gauge includes a radiation source which is longitudinally extendable within said enclosure to desired source depths, and wherein said absorption element represents three different material densities at a single source depth.

34. A method of determining the measurements of a nuclear gauge material measurement device at a field-use site, comprising the steps of:

a. engaging a nuclear gauge having a radiation source capable of emitting radiation and a radiation detector to a nuclear verification device;

b. transmitting radiation from the radiation source into a path defined by the positions of the radiation source, the nuclear gauge verification device, and the radiation detector;

c. positioning a material specimen absorption element configured to simulate a known material density in the radiation path;

d. measuring the radiation emissions generated from said transmitting step received at the radiation detector to establish a nuclear gauge material density reading value;

e. comparing the reading value with a corresponding known material density value associated with the material specimen absorption element, thereby determining the nuclear gauge measurement accuracy; and

further comprising the step of translating one or more of the radiation source and the material specimen absorption element in the radiation path from a first position to a second position by one or more of rotating and translating said absorption element in at least one direction from a first reading position to a second reading position relative to the nuclear gauge radiation source.

35. A method of determining the measurements of a nuclear gauge material measurement device at a field-use site, comprising the steps of:

a. engaging a nuclear gauge having a radiation source capable of emitting radiation and a radiation detector to a nuclear gauge verification device;

b. transmitting radiation from the radiation source into a radiation path defined by the positions of the radiation source, the nuclear gauge verification device, and the radiation detector;

c. positioning a material specimen absorption element configured to simulate a known material density in the radiation path;

d. measuring the radiation emissions generated from said transmitting step received at the radiation detector to establish a nuclear gauge material density reading value; and

e. comparing the reading value with a corresponding known material density value associated with the material specimen absorption element, thereby determining the nuclear gauge measurement accuracy,

wherein said method steps (b), (c), (d) and (e) are repeated at multiple longitudinal depths within the verification device to verify measurement accuracy of the nuclear gauge at corresponding selected radiation depths.

36. A method of determining the measurements of a nuclear gauge material measurement device at a field-use site, comprising the steps of:

a. engaging a nuclear gauge having a radiation source capable of emitting radiation and a radiation detector to a nuclear gauge verification device;

b. transmitting radiation from the radiation source into a radiation path defined by the positions of the radiation source, the nuclear gauge verification device, and the radiation detector;

c. positioning a material specimen absorption element configured to simulate a known material density in the radiation path;

d. measuring the radiation emissions generated from said transmitting step received at the radiation detector to establish a nuclear gauge material density reading value; and

e. comparing the reading value with a corresponding known material density value associated with the material specimen absorption element, thereby determining the nuclear gauge measurement accuracy,

wherein said positioning step further includes the step of positioning a material specimen absorption element in the radiation path to simulate a second material density different from the first material density.

37. A method of determining the measurements of a nuclear gauge material measurement device at a field-use site, comprising the steps of:

a. engaging a nuclear gauge having a radiation source capable of emitting radiation and a radiation detector to a nuclear gauge verification device;

b. transmitting radiation from the radiation source into a radiation path defined by the positions of the radiation source, the nuclear gauge verification device, and the radiation detector;

c. positioning a material specimen absorption element configured to simulate a known material density in the radiation path;

d. measuring the radiation emissions generated from said transmitting step received at the radiation detector to establish a nuclear gauge material density reading value; and

e. comparing the reading value with a corresponding known material density value associated with the material specimen absorption element, thereby determining the nuclear gauge measurement accuracy,

wherein said absorption element is sized and configured to represent two different material densities.

38. A method of determining the measurements of a nuclear gauge material measurement device at a field-use site, comprising the steps of:

a. engaging a nuclear gauge having a radiation source capable of emitting radiation and a radiation detector to a nuclear gauge verification device;

b. transmitting radiation from the radiation source into a radiation path defined by the positions of the radiation source, the nuclear gauge verification device, and the radiation detector;

c. positioning a material specimen absorption element configured to simulate a known material density in the radiation path;

d. measuring the radiation emissions generated from said transmitting step received at the radiation detector to establish a nuclear gauge material density reading value; and

e. comparing the reading value with a corresponding known material density value associated with the material specimen absorption element thereby, determining the nuclear gauge measurement accuracy, and

further comprising the step of re-calibrating the nuclear gauge based upon the measured material density value, wherein said re-calibrating step includes the step of determining at least one correction factor associated with one or more of mechanical geometry changes, electronic changes, and nuclear decay.

39. A method of determining the measurements of a nuclear gauge material measurement device at a field-use site, comprising the steps of:

a. engaging a nuclear gauge having a radiation source capable of emitting radiation and a radiation detector to a nuclear gauge verification device;

b. transmitting radiation from the radiation source into a radiation path defined by the positions of the radiation source, the nuclear gauge verification device, and the radiation detector;

c. positioning a material specimen absorption element configured to simulate a known material density in the radiation path;

d. measuring the radiation emissions generated from said transmitting step received at the radiation detector to establish a nuclear gauge material density reading value; and

e. comparing the reading value with a corresponding known material density value associated with the material specimen absorption element, thereby determining the nuclear gauge measurement accuracy,

wherein said engaging step includes positioning the nuclear gauge radiation source and detector on a planar surface of the verification device to verify measurements taken in the backscatter mode.

40. A method of determining the measurements of a nuclear gauge material measurement device at a field-use site, comprising the steps of:

a. engaging a nuclear gauge having a radiation source capable of emitting radiation and a radiation detector to a nuclear gauge verification device;

b. transmitting radiation from the radiation source into a radiation path defined by the positions of the radiation source the nuclear gauge verification device, and the radiation detector;

c. positioning a material specimen absorption element configured to simulate a known material density in the radiation path;

d. measuring the radiation emissions generated from said transmitting step received at the radiation detector to establish a nuclear gauge material density reading value; and

e. comparing the reading value with a corresponding known material density value associated with the material specimen absorption element, thereby determining the nuclear gauge measurement accuracy, and

further comprising the step of re-calibrating the nuclear gauge including establishing three new gauge counts.

41. A method of representing a solid standard reference block for use in a portable field-usable nuclear gauge measurement verification and/or calibration device, comprising the step of:

simulating a standard reference block by sizing and configuring a material specimen absorption element to represent a known material density and absorption value associated with the standard reference block material when operationally engaged with a nuclear gauge, wherein said simulating step includes one or more of configuring, positioning, and translating said absorption element in a measurement device to represent a plurality of different standard reference block materials when engaged with a nuclear gauge having a radiation source and detector.

42. A method of representing a solid standard reference block for use in a portable field-usable nuclear gauge measurement verification and/or calibration device, comprising the step of:

simulating a standard reference block by sizing and configuring a material specimen absorption element to represent a known material density and absorption value associated with the standard reference block material when operationally engaged with a nuclear gauge, wherein said simulating step includes one or more of configuring, positioning, and translating said absorption element in a measurement device to represent a plurality of different standard reference block materials when engaged with a nuclear gauge having a radiation source and detector, and wherein said source can be manipulated into different source depths in the field useable device, and wherein said representation of a plurality of different standard reference block materials includes representing at least three different material densities at a single source depth.

43. A method of representing a solid standard reference block for use in a portable field-usable nuclear gauge measurement verification and/or calibration device, comprising the step of:

simulating a standard reference block by sizing and configuring a material specimen absorption element to represent a known material density and absorption value associated with the standard reference block material when operationally engaged with a nuclear gauge, wherein said simulating step includes one or more of configuring, positioning, and translating said absorption element in a measurement device to represent a plurality of different standard reference block materials when engaged with a nuclear gauge having a radiation source and detector, and, wherein said source can be manipulated into different source depths in the field useable device, and wherein said simulating step includes simulating a plurality of different standard reference block material densities at a plurality of source depths.