1、Designation: E1931 09E1931 16Standard Guide forNon-computed X-Ray Compton Scatter Tomography1This standard is issued under the fixed designation E1931; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A nu
2、mber in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 PurposeThis guide covers a tutorial introduction to familiarize the reader with the operational capabilities and limitationsinherent in a
3、 single non-computed X-ray Compton Scatter Tomography (CST). Also included is a brief description of the physicsand typical hardware configuration for CST. This single technique is still used for a small number of inspections. This is not meantas comprehensive guide covering the variety of Compton s
4、cattering techniques that are now used for non-destructive testing andsecurity screen screening.1.2 AdvantagesX-ray Compton Scatter Tomography (CST) is a radiologic nondestructive examination method with severaladvantages that include:1.2.1 The ability to perform X-ray examination without access to
5、the opposite side of the examination object;1.2.2 The X-ray beam need not completely penetrate the examination object allowing thick objects to be partially examined.Thick examination objects become part of the radiation shielding thereby reducing the radiation hazard;1.2.3 The ability to examine an
6、d image object subsurface features with minimal influence from surface features;1.2.4 The ability to obtain high-contrast images from low subject contrast materials that normally produce low-contrast imageswhen using traditional transmitted beam X-ray imaging methods; and1.2.5 The ability to obtain
7、depth information of object features thereby providing a three-dimensional examination. The abilityto obtain depth information presupposes the use of a highly collimated detector system having a narrow angle of acceptance.1.3 ApplicationsThis guide does not specify which examination objects are suit
8、able, or unsuitable, for CST. As with mostnondestructive examination techniques, CST is highly application specific thereby requiring the suitability of the method to be firstdemonstrated in the application laboratory. This guide does not provide guidance in the standardized practice or application
9、of CSTtechniques. No guidance is provided concerning the acceptance or rejection of examination objects examined with CST.1.4 LimitationsAs with all nondestructive examination methods, CST has limitations and is complementary to other NDEmethods. Chief among the limitations is the difficulty in perf
10、orming CST on thick sections of high-Z materials. CST is best appliedto thinner sections of lower Z materials. The following provides a general idea of the range of CST applicability when using a 160keV constant potential X-ray source:Material Practical Thickness RangeSteel Up to about 3 mm (18 in.)
11、Aluminum Up to about 25 mm (1 in.)Aerospace composites Up to about 50 mm (2 in.)Polyurethane Foam Up to about 300 mm (12 in.)The limitations of the technique must also consider the required X,Y, and Z axis resolutions, the speed of image formation, imagequality and the difference in the X-ray scatte
12、ring characteristics of the parent material and the internal features that are to beimaged.1.5 The values stated in both inch-pound and SI units are to be regarded separately as the standard. The values given inparentheses are for information only.1.6 This standard does not purport to address all of
13、 the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and to determine the applicability of regulatorylimitations prior to use.1 This guide is under the jurisdiction ofASTM Committee E07 on Non
14、destructive Testing and is the direct responsibility of E07.01 on Radiology (X and Gamma) Method.Current edition approved June 1, 2009June 1, 2016. Published July 2009June 2016. Originally approved in 1997. Last previous edition approved in 20032009 asE1931 - 97E1931(2003). 09. DOI: 10.1520/E1931-09
15、.10.1520/E1931-16.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users
16、 consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12. Referenced Documents2.1 AST
17、M Standards:2E747 Practice for Design, Manufacture and Material Grouping Classification of Wire Image Quality Indicators (IQI) Used forRadiologyE1025 Practice for Design, Manufacture, and Material Grouping Classification of Hole-Type Image Quality Indicators (IQI)Used for RadiologyE1255 Practice for
18、 RadioscopyE1316 Terminology for Nondestructive ExaminationsE1441 Guide for Computed Tomography (CT) ImagingE1453 Guide for Storage of Magnetic Tape Media that Contains Analog or Digital Radioscopic DataE1475 Guide for Data Fields for Computerized Transfer of Digital Radiological Examination DataE16
19、47 Practice for Determining Contrast Sensitivity in Radiology2.2 ANSI/ASNT Standards:3SNT-TC-1A ASNT Recommended Practice for Personnel Qualification and Certification in Nondestructive TestingANSI/ASNT CP-189 Standard for Qualification and Certification in Nondestructive Testing Personnel2.3 Milita
20、ry Standard:MIL-STD-410 Nondestructive Testing Personnel Qualification and Certification42.4 Aerospace Standard:5AIA-NAS-410 Aerospace Industries Association, National Aerospace Standard-4105 Certification and Qualification ofNondestructive Test Personnel62.5 ISO Standard:7ISO 9712 Nondestructive Te
21、stingQualification and Certification of NDT Personnel3. Terminology3.1 Definitions:3.1.1 CST, being a radiologic examination method, uses much the same vocabulary as other X-ray examination methods. Anumber of terms used in this standard are defined in Terminology E1316. It may also be helpful to re
22、ad GuideE1441.4. Summary of Guide4.1 DescriptionCompton Scatter Tomography is a uniquely different nondestructive test method utilizing penetrating X-rayor gamma-ray radiation. Unlike computed tomography (CT), CST produces radioscopic images which are not computed images.Multiple slice images can be
23、 simultaneously produced so that the time per slice image is in the range of a few seconds. CST canproduce images that are thin with respect to the examination object thickness (slice images) and which are at right angles to theX-ray beam. Each two-dimensional slice image (XY axes) is produced at an
24、 incremental distance along and orthogonal to theX-ray beam (Zaxis). A stack of CST images therefore represents a solid volume within the examination object. Each slice imagecontains examination object information which lies predominantly within the desired slice. To make an analogy as to how CSTwor
25、ks, consider a book. The examination object may be larger or smaller (in length, width and depth) then the analogous book.The CST slice images are the pages in the book. Paging through the slice images provides information about examination objectfeatures lying at different depths within the examina
26、tion object.4.2 Image FormationCST produces one or more digital slice plane images per scan. Multiple slice images can be producedin times ranging from a few seconds to a few minutes depending upon the examined area, desired spatial resolution andsignal-to-noise ratio. The image is digital and is ty
27、pically assembled by computer. CST images are free from reconstructionartifacts as the CST image is produced directly and is not a calculated image. Because CST images are digital, they may beenhanced, analyzed, archived and in general handled as any other digital information.4.3 Calibration Standar
28、dsAs with all nondestructive examinations, known standards are required for the calibration andperformance monitoring of the CST method. Practice E1255 calibration block standards that are representative of the actualexamination object are the best means for CST performance monitoring. Conventional
29、radiologic performance measuring devices,such as Test Method E747 and Practice E1025 image quality indicators or Practice E1647 contrast sensitivity gages are designed2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual B
30、ook of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.4 Available from Standardization Documents Order Desk, DODSSP, Bl
31、dg. 4, Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http:/www.dodssp.daps.mil.5 Available from Federal Aviation Administration (FAA), 800 Independence Ave., SW, Washington, DC 20591, http:/www.faa.gov.6 This document has superseded MIL-STD-410; however, MIL-STD-410 is still acceptable t
32、o the FAA7 Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,Switzerland, http:/www.iso.org.E1931 162for transmitted X-ray beam imaging and are of little use for CST. With appropriate calibratio
33、n, CST can be utilized to makethree-dimensional measurements of internal examination object features.5. Significance and Use5.1 Principal Advantage of Compton Scatter TomographyThe principal advantage of CST is the ability to performthree-dimensional X-ray examination without the requirement for acc
34、ess to the back side of the examination object. CST offersthe possibility to perform X-ray examination that is not possible by any other method. The CST sub-surface slice image isminimally affected by examination object features outside the plane of examination. The result is a radioscopic image tha
35、t containsinformation primarily from the slice plane. Scattered radiation limits image quality in normal radiographic and radioscopicimaging. Scatter radiation does not have the same detrimental effect upon CST because scatter radiation is used to form the image.In fact, the more radiation the exami
36、nation object scatters, the better the CST result. Low subject contrast materials that cannotbe imaged well by conventional radiographic and radioscopic means are often excellent candidates for CST. Very high contrastsensitivities and excellent spatial resolution are possible with CST tomography.5.2
37、 LimitationsAs with any nondestructive testing method, CST has its limitations. The technique is useful on reasonablythick sections of low-density materials. While a 25 mm (1 in.) depth in aluminum or 50 mm (2 in.) in plastic is achievable, theexamination depth is decreased dramatically as the mater
38、ial density increases. Proper image interpretation requires the use ofstandards and examination objects with known internal conditions or representative quality indicators (RQIs). The examinationvolume is typically small, on the order of a few cubic inches and may require a few minutes to image. The
39、refore, completelyexamining large structures with CST requires intensive re-positioning of the examination volume that can be time-consuming. Aswith other penetrating radiation methods, the radiation hazard must be properly addressed.6. Basis of Application6.1 Personnel Qualification is subject to c
40、ontractual agreement between the parties using or referencing this standard.6.1.1 If specified in the contractual agreement, personnel performing examinations to this standard shall be qualified inaccordance with a nationally or internationally recognized NDT personnel qualification practice or stan
41、dard such as ANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, MIL-STD-410E, ISO 9712, or a similar document and certified by the employer or certifyingagency, as applicable. The practice or standard used and its applicable revision shall be identified in the contractual agreementbetween the using parties.7. Te
42、chnical Description7.1 General Description of Compton Scatter TomographyTransmitted beam radiologic techniques used in radiography,radioscopy and computed tomography have dominated the use of penetrating radiation for industrial nondestructive examination.The transmitted beam technique depends upon
43、the penetrating radiation attenuation mechanisms of photoelectric absorption andCompton scattering. For low- Z materials at energies up to about 50 keV, the photoelectric effect is the dominant attenuationmechanism.As X-ray energy increases, Compton scattering becomes the dominant attenuation mechan
44、ism. Pair production comesinto play above 1.02 MeV and can become the dominant effect for higher X-ray energies. The following relationships are plottedin Fig. 1 and show the approximate dependence of the photoelectric effect and Compton scattering upon target material atomicFIG. 1 Relationship Betw
45、een Photoelectric, Compton, and Pair Production EffectsPhotoelectric Effect: = Z 5 / E 7/2Compton Scattering: = Z / EPair Production : = Z 2 (lnE - constant)E1931 163number (Z) and incident X-ray energy (E:):Photoelectric Effect Z 5 / E 7/2Compton Scattering Z / EPair Production: Z 2 (lnE - constant
46、)The terms , , and represent the cross sections of the photoelectric, Compton scatter and pair-production interaction of a givenX-ray photon that has energy level E. There is no analytic expression for the probability of photoelectric absorption as it variesas a function of E and Z. For the gamma an
47、d X-ray energies of interest, the exponent of Z can vary between 4 and 5.8 The greenlines are contours where the indicated cross sections are equal. Since the cross sections are proportional to the probability of theparticular type of interaction, moving left to right in the graph, the green lines r
48、epresent the boundaries of the regions where thephotoelectric, Compton and pair-production events are dominant, respectively. The graph is useful for understanding the X-rayproperties of a material, by knowing its predominant mass number Z. For example, it could be used to estimate its interactionre
49、gime based on the Z of the material and energy of interrogation photons.7.1.1 CST is best suited for lower Z materials such as aluminum ( Z=13 ) using a commercially available 160 keV X-raygenerating system. Somewhat higher Z materials may be examined by utilizing a higher energy X-ray generator rated at 225, 320,or 450 keV.7.1.2 It is useful to envision the CST process as one where the X-rays that produce the CST image originate from many discretepoints within the examined volume. Each Compton scatter event generates a lower energy X-ray X ray that e
