1、Designation: C1718 10Standard Test Method forNondestructive Assay of Radioactive Material byTomographic Gamma Scanning1This standard is issued under the fixed designation C1718; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the y
2、ear of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the nondestructive assay(NDA) of gamma ray emitting radionuclides inside containersu
3、sing tomographic gamma scanning (TGS). High resolutiongamma ray spectroscopy is used to detect and quantify theradionuclides of interest. The attenuation of an external gammaray transmission source is used to correct the measurement ofthe emission gamma rays from radionuclides to arrive at aquantita
4、tive determination of the radionuclides present in theitem.1.2 The TGS technique covered by the test method may beused to assay scrap or waste material in cans or drums in the 1to 500 litre volume range. Other items may be assayed as well.1.3 The test method will cover two implementations of theTGS
5、procedure: (1) Isotope Specific Calibration that usesstandards of known radionuclide masses (or activities) todetermine system response in a mass (or activity) versuscorrected count rate calibration, that applies to only thosespecific radionuclides for which it is calibrated, and (2)Response Curve C
6、alibration that uses gamma ray standards todetermine system response as a function of gamma ray energyand thereby establishes calibration for all gamma emittingradionuclides of interest.1.4 This test method will also include a technique to extendthe range of calibration above and below the extremes
7、of themeasured calibration data.1.5 The assay technique covered by the test method isapplicable to a wide range of item sizes, and for a wide rangeof matrix attenuation. The matrix attenuation is a function ofthe matrix composition, photon energy, and the matrix density.The matrix types that can be
8、assayed range from lightcombustibles to cemented sludge or concrete. It is particularlywell suited for items that have heterogeneous matrix materialand non-uniform radioisotope distributions. Measured trans-mission values should be available to permit valid attenuationcorrections, but are not needed
9、 for all volume elements in thecontainer, for example, if interpolation is justified.1.6 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7 This standard does not purport to address all of thesafety concerns, if any, associated
10、 with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C1030 Test Method for Determination of Plutonium Isoto-pic Comp
11、osition by Gamma-Ray SpectrometryC1128 Guide for Preparation of Working Reference Mate-rials for Use in Analysis of Nuclear Fuel Cycle MaterialsC1490 Guide for the Selection, Training and Qualificationof Nondestructive Assay (NDA) PersonnelC1156 Guide for Establishing Calibration for a Measure-ment
12、Method Used to Analyze Nuclear Fuel Cycle Mate-rialsC1592 Guide for Nondestructive Assay MeasurementsC1673 Terminology of C26.10 NondestructiveAssay Meth-ods2.2 ANSI Standards:3ANSI N15.37 Guide to the Automation of NondestructiveAssay Systems for Nuclear Materials Control2.3 Nuclear Regulatory Comm
13、ission (NRC) Guides4NRC Guide 5.9 Guidelines for Germanium SpectroscopySystems for Measurement of Special Nuclear Material,Revision 2, December 19831This test method is under the jurisdiction of ASTM Committee C26 on NuclearFuel Cycle and is the direct responsibility of Subcommittee C26.10 on NonDes
14、tructive Assay.Current edition approved Jan. 1, 2010. Published February 2010. DOI: 10.1520/C1718-10.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards D
15、ocument Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.4Available from U.S. Nuclear Regulatory Commission, Washington, DC 20555-0001, http:/nrc.gov.1Copyright ASTM International, 100 Barr
16、Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.NRC Guide 5.53 Qualification, Calibration, and Error Esti-mation Methods for Nondestructive Assay, Revision 1,February 19843. Terminology3.1 Definitions: Terms shall be defined in accordance withTerminology C1673 except for t
17、he following:3.1.1 Algebraic Reconstruction Technique (ART), nimagereconstruction technique typically used in the TGS method toobtain the transmission map as a function of atomic number (Z)and gamma ray energy (1).53.1.2 aperture, nthe terminology applies to the width ofthe detector collimator. In t
18、he case of a diamond collimator, theaperture is defined as the distance between the parallel sides ofthe diamond. In some designs, the detector collimator can be atruncated diamond that consists of flat trim pieces at the leftand right corners of the diamond. This type of collimator isusually design
19、ed with the distance between the trim pieces setequal to the distance between the parallel surfaces (aperture).3.1.3 voxel, nvolume element; the three-dimensional ana-log of a two-dimensional pixel. Typically 5 cm on a side for a208 L drum.3.1.3.1 DiscussionThe full container volume will be di-vided
20、 into a number of smaller volume elements (typically1002000 or typically 0.1 % of the total container volume),which are not necessarily rectilinear.3.1.4 Beers Law, nthe law states that the fraction ofuncollided gamma rays transmitted through layers of equalthickness of an absorber is a constant. Ma
21、thematically, BeersLaw can be expressed as follows:T 5II05 expHr r tJIn the above equation, I0is the intensity of a pencil beam ofgamma rays incident on a uniform layer of absorber, I is thetransmitted intensity through the layer, /r is the mass attenu-ation coefficient of the absorber material, r i
22、s the density of theabsorber and t is the thickness of the layer. For a heterogeneousmaterial the exponent would be integrated along the ray path.3.1.5 expectation maximization (EM), nimage reconstruc-tion technique typically used in the TGS method to solve forthe emission map as a function of gamma
23、 ray energy (2, 3).3.1.6 grab (or view), na single measurement of the scan,where the scan sequence consists of measurements at variousheights, rotational positions, and translation positions of theassay item.3.1.7 map (transmission and emission), na voxel by voxelrecord of the matrix density or line
24、ar attenuation coefficient(transmission map) or a voxel by voxel record of radionuclidecontent (emission map).3.1.8 material basis set (or MBS), nthe method where thelinear attenuation coefficient map for a matrix material isdetermined in terms of 2 or 3 basis elements that span the Zrange of intere
25、st (4).3.1.9 non-negative least squares (NNLS), nconstrainedleast squares fitting algorithm used in TGS analysis to obtainan initial estimate of the transmission map.3.1.10 pre-scan, na preliminary scan of an assay itememployed by some TGS implementations to optimize the scanprotocol on an item-by-i
26、tem basis.3.1.11 scan, nsequence of measurements at variousheights, rotational positions, and translation positions of theassay item.3.1.12 response function, ndetector efficiency (absolute orrelative) as a function of measurement locus and gamma rayenergy.3.1.13 tomography, nthe mathematical method
27、 in whichgamma ray measurements are used to determine the attenuationand emission characteristics of an item on a voxel-by-voxelbasis.3.1.14 translation, nthe relative motion in the horizontaldirection of the item to be measured perpendicular to thetransmission source-detector axis.3.1.15 TGS Number
28、, nuncalibrated result of a TGS analy-sis representing count rate corrected for geometrical efficiency,gamma ray attenuation , and rate loss at a given emissiongamma ray energy, proportional to the mass or activity of aspecific radionuclide.3.1.16 view, nsee grab.4. Summary of Test Method4.1 Assay o
29、f the radionuclides of interest is accomplishedby measuring the intensity of one or more characteristicgamma rays from each radionuclide utilizing TGS techniques.TGS techniques include translating, rotating and verticallyscanning the assay item such that a 3-dimensional (3D) imagecan be reconstructe
30、d from the data. Generally two 3D imagesare constructed; a transmission image and a passive emissionimage. Corrections are made for count rate-related losses andattenuation by the matrix in which the nuclear material isdispersed. The calibration then provides the relationship be-tween observed gamma
31、 ray intensity and radionuclide content.4.2 Calibration is performed using standards containing theradionuclides to be assayed or using a mixture of radionuclidesemitting gamma rays that span the energy range of interest. Theactivities or masses of the radionuclides and the gamma rayyields are trace
32、able to a national measurement database.4.2.1 Using a traceable mixed gamma ray standard thatspans the energy range of interest will enable the determinationof the TGS calibration parameters at any gamma ray energy ofinterest, not just those that are present in the calibrationstandard. A calibration
33、 curve is generated that parameterizesthe variation of the TGS calibration factor as a function ofgamma ray energy.4.3 The assay item is rotated about its vertical axis. Con-currently, the relative position of the assay item and detectorare translated. This is repeated for every vertical segment.Dur
34、ing this process, a series of measurements (grabs) are takenof gamma rays corresponding to the transmission source andthe emission sources. A transmission scan is performed withthe transmission source exposed. A separate emission scan isperformed with the transmission source shielded.5The boldface n
35、umbers in parentheses refer to a list of references at the end ofthis standard.C1718 1024.3.1 From the transmission measurements, a 3D map of theaverage linear attenuation coefficient across of each voxel isdetermined.4.3.2 From the emission measurements, a 3D map of thelocation of the gamma emittin
36、g radionuclides is determined.These 3D maps are typically low spatial resolution (forexample, approximately110 th the diameter would be a typicalcharacteristic dimension).4.3.3 Through a voxel by voxel application of Beers Law,the emission source strength is corrected for the attenuation ofthe matri
37、x material.4.4 Count rate-dependent losses from pulse pile-up andanalyzer deadtime are monitored and corrected.4.5 The TGS determines an estimate of the average attenu-ation coefficient of each voxel in a layer of matrix using anover determined set of transmission measurements.4.6 Acollimator is use
38、d in front of the detector to restrict themeasurement to a well-defined solid angle.4.7 The TGS technique assumes the following item charac-teristics:4.7.1 The particles containing the radionuclides of interestare small enough to minimize self-absorption of emittedgamma radiation. Corrections to sle
39、f-attenuation may be ap-plied post TGS analysis, but is outside the scope of thisstandard.4.7.2 The mixture of material within each item voxel issufficiently uniform that an attenuation correction factor, com-puted from a measurement of gamma ray transmission throughthe voxel, is appropriate.4.8 Typ
40、ically, a single isotope of an element is measured,therefore when the total element mass is required, it isnecessary to apply a known or estimated radionuclide/totalratio to the radionuclide assay value to determine the totalelement content (see Test Method C1030).5. Significance and Use5.1 The TGS
41、provides a nondestructive means of mappingthe attenuation characteristics and the distribution of theradionuclide content of items on a voxel by voxel basis.Typically in a TGS analysis a vertical layer (or segment) of anitem will be divided into a number of voxels. By comparison,a segmented gamma sc
42、anner (SGS) can determine matrixattenuation and radionuclide concentrations only on a segmentby segment basis.5.2 It has been successfully used to quantify238Pu,239Pu,and235U. SNM loadings from 0.5 g to 200 g of239Pu (5, 6),from1gto25gof235U (7), and from 0.1 to1gof238Pu havebeen successfully measur
43、ed. The TGS technique has also beenapplied to assaying radioactive waste generated by nuclearpower plants (NPP). Radioactive waste from NPP is dominatedby activation products (forexample,54Mn,58Co,60Co,110mAg) and fission products (forexample,137Cs,134Cs). The radionuclide activities measured inNPP
44、waste is in the range from 3.7E+04 Bq to 1.0E+07 Bq.Some results of TGS application to non-SNM radionuclidescan be found in the literature (8).5.3 The TGS technique is well suited for assaying items thathave heterogeneous matrices and that contain a non-uniformradionuclide distribution.5.4 Since the
45、 analysis results are obtained on a voxel byvoxel basis, the TGS technique can in many situations yieldmore accurate results when compared to other gamma raytechniques such as SGS.5.5 In determining the radionuclide distribution inside anitem, the TGS analysis explicitly takes into account the cross
46、talk between various vertical layers of the item.5.6 The TGS analysis technique uses a material basis setmethod that does not require the user to select a massattenuation curve apriori, provided the transmission source hasat least 2 gamma lines that span the energy range of interest.5.7 Acommerciall
47、y available TGS system consists of build-ing blocks that can easily be configured to operate the systemin the SGS mode or in a far-field geometry.5.8 The TGS provides 3-dimensional maps of gamma rayattenuation and radionuclide concentration within an item thatcan be used as a diagnostic tool.5.9 Ite
48、m preparation is limited to avoiding large quantitiesof heavily attenuating materials (such as lead shielding) inorder to allow sufficient transmission through the container andthe matrix.6. Interferences6.1 Radionuclides may be present in an item that producegamma rays with energies the same as or
49、very nearly equal tothe gamma rays of the radionuclide to be measured or of thetransmission source. There may be instances where emissiongamma rays from multiple radionuclides interfere with oneanother or with a gamma ray present in the background. A fewexamples are given below:6.1.1 Interference with Transmission Gamma Rays:6.1.1.1 In TGS systems where an152Eu source is used as thetransmission source, one has to consider the following inter-ferences while assaying plutonium containing waste drums. (1)Transmission data from the 121.78 keV gamma ray from152
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