ASTM E1931-16(2022)
(Guide)Standard Guide for Non-computed X-Ray Compton Scatter Tomography
Standard Guide for Non-computed X-Ray Compton Scatter Tomography
SIGNIFICANCE AND USE
5.1 Principal Advantage of Compton Scatter Tomography—The principal advantage of CST is the ability to perform three-dimensional X-ray examination without the requirement for access to the back side of the examination object. CST offers the possibility to perform X-ray examination that is not possible by any other method. The CST sub-surface slice image is minimally affected by examination object features outside the plane of examination. The result is a radioscopic image that contains information primarily from the slice plane. Scattered radiation limits image quality in normal radiographic and radioscopic imaging. 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 examination object scatters, the better the CST result. Low subject contrast materials that cannot be imaged well by conventional radiographic and radioscopic means are often excellent candidates for CST. Very high contrast sensitivities and excellent spatial resolution are possible with CST tomography.
5.2 Limitations—As with any nondestructive testing method, CST has its limitations. The technique is useful on reasonably thick sections of low-density materials. While a 25 mm (1 in.) depth in aluminum or 50 mm (2 in.) in plastic is achievable, the examination depth is decreased dramatically as the material density increases. Proper image interpretation requires the use of standards and examination objects with known internal conditions or representative quality indicators (RQIs). The examination volume is typically small, on the order of a few cubic inches and may require a few minutes to image. Therefore, completely examining large structures with CST requires intensive re-positioning of the examination volume that can be time-consuming. As with other penetrating radiation methods, the radiation hazard must be properly addressed.
SCOPE
1.1 Purpose—This guide covers a tutorial introduction to familiarize the reader with the operational capabilities and limitations inherent in a single non-computed X-ray Compton Scatter Tomography (CST). Also included is a brief description of the physics and typical hardware configuration for CST. This single technique is still used for a small number of inspections. This is not meant as comprehensive guide covering the variety of Compton scattering techniques that are now used for non-destructive testing and security screen screening.
1.2 Advantages—X-ray Compton Scatter Tomography (CST) is a radiologic nondestructive examination method with several advantages that include:
1.2.1 The ability to perform X-ray examination without access to 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 and 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 images when using traditional transmitted beam X-ray imaging methods; and
1.2.5 The ability to obtain depth information of object features thereby providing a three-dimensional examination. The ability to obtain depth information presupposes the use of a highly collimated detector system having a narrow angle of acceptance.
1.3 Applications—This guide does not specify which examination objects are suitable, or unsuitable, for CST. As with most nondestructive examination techniques, CST is highly application specific thereby requiring the suitability of the method to be first demonstrated in the application laboratory. This guide does not provide guidance in the standardized practice or application of CST techniques. No guidance is provided co...
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This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E1931 − 16 (Reapproved 2022)
Standard Guide for
Non-computed X-Ray Compton Scatter Tomography
This standard is issued under the fixed designation E1931; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope provided concerning the acceptance or rejection of examina-
tion objects examined with CST.
1.1 Purpose—This guide covers a tutorial introduction to
familiarize the reader with the operational capabilities and 1.4 Limitations—As with all nondestructive examination
limitations inherent in a single non-computed X-ray Compton
methods, CST has limitations and is complementary to other
ScatterTomography(CST).Alsoincludedisabriefdescription NDE methods. Chief among the limitations is the difficulty in
ofthephysicsandtypicalhardwareconfigurationforCST.This
performing CST on thick sections of high-Z materials. CST is
single technique is still used for a small number of inspections. best applied to thinner sections of lower Z materials. The
This is not meant as comprehensive guide covering the variety
following provides a general idea of the range of CST
of Compton scattering techniques that are now used for applicability when using a 160 keV constant potential X-ray
non-destructive testing and security screen screening.
source:
Material Practical Thickness Range
1.2 Advantages—X-ray Compton Scatter Tomography
(CST) is a radiologic nondestructive examination method with
Steel Up to about 3 mm ( ⁄8 in.)
several advantages that include:
Aluminum Up to about 25 mm (1 in.)
Aerospace composites Up to about 50 mm (2 in.)
1.2.1 The ability to perform X-ray examination without
Polyurethane Foam Up to about 300 mm (12 in.)
access to the opposite side of the examination object;
The limitations of the technique must also consider the
1.2.2 The X-ray beam need not completely penetrate the
required X, Y, and Z axis resolutions, the speed of image
examination object allowing thick objects to be partially
formation, image quality and the difference in the X-ray
examined. Thick examination objects become part of the
scattering characteristics of the parent material and the internal
radiation shielding thereby reducing the radiation hazard;
features that are to be imaged.
1.2.3 The ability to examine and image object subsurface
features with minimal influence from surface features;
1.5 The values stated in both inch-pound and SI units are to
1.2.4 The ability to obtain high-contrast images from low
be regarded separately as the standard. The values given in
subject contrast materials that normally produce low-contrast
parentheses are for information only.
imageswhenusingtraditionaltransmittedbeamX-rayimaging
1.6 This standard does not purport to address all of the
methods; and
safety concerns, if any, associated with its use. It is the
1.2.5 The ability to obtain depth information of object
responsibility of the user of this standard to establish appro-
features thereby providing a three-dimensional examination.
priate safety, health, and environmental practices and deter-
The ability to obtain depth information presupposes the use of
mine the applicability of regulatory limitations prior to use.
a highly collimated detector system having a narrow angle of
1.7 This international standard was developed in accor-
acceptance.
dance with internationally recognized principles on standard-
1.3 Applications—Thisguidedoesnotspecifywhichexami-
ization established in the Decision on Principles for the
nation objects are suitable, or unsuitable, for CST. As with
Development of International Standards, Guides and Recom-
most nondestructive examination techniques, CST is highly
mendations issued by the World Trade Organization Technical
application specific thereby requiring the suitability of the
Barriers to Trade (TBT) Committee.
method to be first demonstrated in the application laboratory.
This guide does not provide guidance in the standardized
2. Referenced Documents
practice or application of CST techniques. No guidance is
2.1 ASTM Standards:
This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-
tiveTesting and is the direct responsibility of E07.01 on Radiology (X and Gamma)
Method. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
CurrenteditionapprovedJune1,2022.PublishedJuly2022.Originallyapproved contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
in 1997. Last previous edition approved in 2016 as E1931 – 16. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
E1931-16R22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1931 − 16 (2022)
E747 Practice for Design, Manufacture and Material Group- respect to the examination object thickness (slice images) and
ing Classification of Wire Image Quality Indicators (IQI) which are at right angles to the X-ray beam. Each two-
Used for Radiology dimensional slice image (X–Y axes) is produced at an incre-
E1025 Practice for Design, Manufacture, and Material mental distance along and orthogonal to the X-ray beam
Grouping Classification of Hole-Type Image Quality In-
(Z–axis). A stack of CST images therefore represents a solid
dicators (IQI) Used for Radiography volume within the examination object. Each slice image
E1255 Practice for Radioscopy
contains examination object information which lies predomi-
E1316 Terminology for Nondestructive Examinations nantly within the desired slice. To make an analogy as to how
E1441 Guide for Computed Tomography (CT)
CST works, consider a book. The examination object may be
E1453 Guide for Storage of Magnetic Tape Media that larger or smaller (in length, width and depth) then the analo-
Contains Analog or Digital Radioscopic Data
gous book. The CST slice images are the pages in the book.
E1475 Guide for Data Fields for Computerized Transfer of
Paging through the slice images provides information about
Digital Radiological Examination Data
examination object features lying at different depths within the
E1647 Practice for Determining Contrast Sensitivity in Ra-
examination object.
diology
4.2 Image Formation—CST produces one or more digital
2.2 ANSI/ASNT Standards:
slice plane images per scan. Multiple slice images can be
SNT-TC-1A ASNT Recommended Practice for Personnel
producedintimesrangingfromafewsecondstoafewminutes
Qualification and Certification in Nondestructive Testing
depending upon the examined area, desired spatial resolution
ANSI/ASNT CP-189 Standard for Qualification and Certifi-
and signal-to-noise ratio. The image is digital and is typically
cation in Nondestructive Testing Personnel
assembled by computer. CST images are free from reconstruc-
2.3 Military Standard:
tion artifacts as the CST image is produced directly and is not
MIL-STD-410 Nondestructive Testing Personnel Qualifica-
a calculated image. Because CST images are digital, they may
tion and Certification
be enhanced, analyzed, archived and in general handled as any
2.4 Aerospace Standard:
other digital information.
AIA-NAS-410 Aerospace Industries Association, National
Aerospace Standard-4105 Certification and Qualification 4.3 Calibration Standards—As with all nondestructive
of Nondestructive Test Personnel examinations, known standards are required for the calibration
and performance monitoring of the CST method. Practice
2.5 ISO Standard:
E1255 calibration block standards that are representative of the
ISO 9712 Nondestructive Testing—Qualification and Certi-
actual examination object are the best means for CST perfor-
fication of NDT Personnel
mance monitoring. Conventional radiologic performance mea-
3. Terminology
suring devices, such as Test Method E747 and Practice E1025
image quality indicators or Practice E1647 contrast sensitivity
3.1 Definitions:
gagesaredesignedfortransmittedX-raybeamimagingandare
3.1.1 CST, being a radiologic examination method, uses
of little use for CST. With appropriate calibration, CST can be
much the same vocabulary as other X-ray examination meth-
utilized to make three-dimensional measurements of internal
ods. A number of terms used in this standard are defined in
examination object features.
Terminology E1316. It may also be helpful to read Guide
E1441.
5. Significance and Use
4. Summary of Guide
5.1 Principal Advantage of Compton Scatter Tomography—
4.1 Description—Compton Scatter Tomography is a
The principal advantage of CST is the ability to perform
uniquely different nondestructive test method utilizing pen-
three-dimensional X-ray examination without the requirement
etrating X-ray or gamma-ray radiation. Unlike computed
for access to the back side of the examination object. CST
tomography(CT),CSTproducesradioscopicimageswhichare
offers the possibility to perform X-ray examination that is not
not computed images. Multiple slice images can be simultane-
possible by any other method. The CST sub-surface slice
ously produced so that the time per slice image is in the range
image is minimally affected by examination object features
of a few seconds. CST can produce images that are thin with
outside the plane of examination. The result is a radioscopic
image that contains information primarily from the slice plane.
Scattered radiation limits image quality in normal radiographic
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
and radioscopic imaging. Scatter radiation does not have the
4th Floor, New York, NY 10036, http://www.ansi.org.
Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,
same detrimental effect upon CST because scatter radiation is
Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http://
used to form the image. In fact, the more radiation the
www.dodssp.daps.mil.
5 examination object scatters, the better the CST result. Low
Available from Federal Aviation Administration (FAA), 800 Independence
subject contrast materials that cannot be imaged well by
Ave., SW, Washington, DC 20591, http://www.faa.gov.
This document has superseded MIL-STD-410; however, MIL-STD-410 is still
conventional radiographic and radioscopic means are often
acceptable to the FAA
excellent candidates for CST. Very high contrast sensitivities
Available from International Organization for Standardization (ISO), ISO
and excellent spatial resolution are possible with CST tomog-
Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
Geneva, Switzerland, http://www.iso.org. raphy.
E1931 − 16 (2022)
5.2 Limitations—As with any nondestructive testing
method, CST has its limitations. The technique is useful on
reasonably thick sections of low-density materials. While a 25
mm (1 in.) depth in aluminum or 50 mm (2 in.) in plastic is
achievable, the examination depth is decreased dramatically as
the material density increases. Proper image interpretation
requires the use of standards and examination objects with
known internal conditions or representative quality indicators
(RQIs). The examination volume is typically small, on the
order of a few cubic inches and may require a few minutes to
image. Therefore, completely examining large structures with
CST requires intensive re-positioning of the examination
volume that can be time-consuming.As with other penetrating
radiation methods, the radiation hazard must be properly
addressed.
FIG. 1 Relationship Between Photoelectric, Compton, and Pair
6. Basis of Application
Production Effects
5 7/2
6.1 Personnel Qualification is subject to contractual agree-
Photoelectric Effect: τ = Z / E
Compton Scattering: σ = Z / E
ment between the parties using or referencing this standard.
Pair Production : κ = Z (lnE - constant)
6.1.1 If specified in the contractual agreement, personnel
performing examinations to this standard shall be qualified in
accordance with a nationally or internationally recognized
moving left to right in the graph, the green lines represent the
NDT personnel qualification practice or standard such as
boundaries of the regions where the photoelectric, Compton
ANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, MIL-STD-
and pair-production events are dominant, respectively. The
410E, ISO 9712, or a similar document and certified by the
graph is useful for understanding the X-ray properties of a
employer or certifying agency, as applicable. The practice or
material, by knowing its predominant mass number Z. For
standard used and its applicable revision shall be identified in
example, it could be used to estimate its interaction regime
the contractual agreement between the using parties.
based on the Z of the material and energy of interrogation
photons.
7. Technical Description
7.1.1 CST is best suited for lower Z materials such as
7.1 General Description of Compton Scatter Tomography—
aluminum ( Z=13 ) using a commercially available 160 keV
Transmitted beam radiologic techniques used in radiography,
X-ray generating system. Somewhat higher Z materials may be
radioscopy and computed tomography have dominated the use
examined by utilizing a higher energy X-ray generator rated at
of penetrating radiation for industrial nondestructive examina-
225, 320, or 450 keV.
tion. The transmitted beam technique depends upon the pen-
7.1.2 It is useful to envision the CST process as one where
etrating radiation attenuation mechanisms of photoelectric
the X-rays that produce the CST image originate from many
absorption and Compton scattering. For low- Z materials at
discrete points within the examined volume. Each Compton
energies up to about 50 keV, the photoelectric effect is the
scatter event generates a lower energy X ray that emanates
dominant attenuation mechanism. As X-ray energy increases,
from the scattering site. Singly scattered X rays that reach the
Compton scattering becomes the dominant attenuation mecha-
detector carry information about the examination object mate-
nism.Pairproductioncomesintoplayabove1.02MeVandcan
rial characteristics at the site where it was generated. The
become the dominant effect for higher X-ray energies. The
scatter radiation is also affected by the material through which
following relationships are plotted in Fig. 1 and show the
it passes on the way to the detector. The external source of
approximate dependence of the photoelectric effect and Co
...
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