ASTM E3398-23

Standard Guide for Digital Neutron Radiography

SIGNIFICANCE AND USE
4.1 Purpose—Practices to be employed for the radiographic examination of materials and components with neutrons using digital neutron detectors are outlined herein. They are intended as a guide for the assessment of a digital neutron radiograph’s characteristics. For information on neutron beam lines for imaging and film neutron radiography, refer to Guide E748.  
4.2 Limitations—Acceptance standards have not been established for any material or production process. Neutron radiography, whether performed by means of a reactor, an accelerator, subcritical assembly, or radioactive source, will be consistent in sensitivity and spatial resolution only if the consistency of all details of the technique, such as neutron source, collimation, geometry, imaging system, etc., are maintained. This guide is limited to the use of digital neutron detectors in combination with neutron conversion materials for image recording. This guide is intended for use with thermal and cold neutron spectrums. The production of thermal neutron radiographs by employing the use of film and appropriate conversion screens is covered in Guide E748.  
4.3 Interpretation and Acceptance Standards—Interpretat- ion and acceptance standards are not covered by this guide. Designation of accept-reject standards is recognized to be within the cognizance of product specifications.  
4.4 Other Aspects of the Neutron Radiographic Process—For many important aspects of neutron radiography such as technique, files, viewing of radiographs, storage of radiographs, film processing, and record keeping, refer to Guide E94, which covers these aspects for X-ray radiography. (See Section 2.)
SCOPE
1.1 This guide covers the evaluation, qualification, and quantification of digital neutron images. These images can be acquired by many methods, including: neutron sensitive imaging plates (Computed Radiography – CR), Digital Detector Arrays – DDA’s (amorphous silicon, CMOS, CCD, etc.), micro-channel plates, neutron sensitive fluoroscopes, neutron sensitive scintillators coupled to optical cameras, digitized radiographic films, and linear diode arrays.  
1.2 This guide does not purport to establish what is considered an acceptable image but is intended to only give guidance on digital neutron imaging, as well as image quality metrics of importance, and how they can be measured and reported.  
1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Published
• Publication Date: 30-Jun-2023
• ICS: 11.040.50 - Radiographic equipment
• ICS: 35.240.80 - IT applications in health care technology
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.05 - Radiology (Neutron) Method

Relations

• Refers: ASTM E1316-24 - Standard Terminology for <?Pub Dtl?>Nondestructive Examinations
• Effective Date: 01-Feb-2024
• Refers: ASTM E803-20 - Standard Test Method for Determining the <emph type="ital">L/D&#x2009;</emph>Ratio of Neutron Radiography Beams
• Effective Date: 01-Jul-2020
• Refers: ASTM E1316-19b - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2019
• Refers: ASTM E545-19 - Standard Test Method for Determining Image Quality in Direct Thermal Neutron Radiographic Examination
• Effective Date: 01-May-2019
• Refers: ASTM E748-19 - Standard Guide for Thermal Neutron Radiography of Materials
• Effective Date: 01-May-2019
• Refers: ASTM E1316-19 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Mar-2019
• Refers: ASTM E1316-18 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Jan-2018
• Refers: ASTM E803-17 - Standard Test Method for Determining the <emph type="ital">L/D&#x2009;</emph>Ratio of Neutron Radiography Beams
• Effective Date: 01-Nov-2017
• Refers: ASTM E1316-17a - Standard Terminology for Nondestructive Examinations
• Effective Date: 15-Jun-2017
• Refers: ASTM E1316-17 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2017
• Refers: ASTM E1316-16a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Aug-2016
• Refers: ASTM E748-16 - Standard Guide for Thermal Neutron Radiography of Materials
• Effective Date: 15-Feb-2016
• Refers: ASTM E1316-16 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Feb-2016
• Refers: ASTM E1316-15a - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Dec-2015
• Refers: ASTM E1316-15 - Standard Terminology for Nondestructive Examinations
• Effective Date: 01-Sep-2015

Overview

ASTM E3398-23: Standard Guide for Digital Neutron Radiography provides comprehensive guidelines for conducting radiographic examinations of materials and components using neutrons with digital neutron detectors. Developed by ASTM International, this standard helps ensure consistent evaluation, qualification, and quantification of digital neutron images. It offers practical procedures on utilizing various types of digital neutron detectors and conversion materials, and is intended for thermal and cold neutron spectrums. Digital neutron radiography presents several advantages over traditional film methods, including shorter exposure times, digital file management, and advanced imaging options.

Key Topics

• Digital Neutron Imaging Methods:

  • Computed Radiography (CR) using neutron-sensitive imaging plates.
  • Digital Detector Arrays (DDAs) such as amorphous silicon, CMOS, and CCD sensors.
  • Camera-Based Systems (CBS) with neutron-sensitive scintillators.
  • Other methods, including micro-channel plates and digitized radiographic film.

• Image Quality Assessment:

  • Guidance on evaluating contrast, spatial resolution, and signal-to-noise ratio (SNR).
  • Use of reference objects like line pair gauges and contrast sensitivity indicators.
  • Correction of bad pixels, background normalization, and post-processing for image enhancement.

• Neutron Conversion and Detection:

  • Usage of neutron absorbers (e.g., gadolinium, boron) to convert neutrons into detectable radiation.
  • Considerations for detector efficiency, gamma sensitivity, and field of view.

• Tomography and Advanced Techniques:

  • Application of digital neutron radiography to 3D image reconstruction (tomography).
  • Possibility for dynamic imaging and advanced investigative methods such as phase contrast and Bragg-edge imaging.

Applications

Digital neutron radiography, guided by ASTM E3398-23, is widely used in:

• Industrial Non-Destructive Testing (NDT):

  • Inspection of complex assemblies, internal features, or encapsulated components that are challenging for other imaging methods.
  • Evaluation of high-density or multi-layered materials not easily penetrated by X-rays.

• Research and Development:

  • Materials characterization, quality control, and comparative imaging in laboratories.
  • Dynamic studies requiring fast digital readout and the ability to analyze time-resolved processes.

• Aerospace & Defense:

  • Inspection of turbine blades, rocket motors, and pyrotechnical devices for structural integrity.
  • Validation of internal mechanisms without disassembly.

• Cultural Heritage and Archaeology:

  • Non-invasive examination of artifacts and valuable historical objects to study manufacturing techniques or preservation status.

Benefits of digital neutron radiography include faster data acquisition, improved contrast and resolution options, easier archiving and sharing of digital images, and adaptability to advanced computing and analysis techniques.

Related Standards

ASTM E3398-23 references several other important ASTM standards, such as:

• ASTM E748: Guide for Thermal Neutron Radiography - foundational information on traditional film-based neutron imaging and beam line setup.
• ASTM E94: Guide for Radiographic Examination Using Industrial Radiographic Film - referenced for imaging, file handling, and storage aspects.
• ASTM E545: Test Method for Determining Image Quality in Direct Thermal Neutron Radiographic Examination.
• ASTM E803: Method for Determining the L/D Ratio of Neutron Radiography Beams.
• ASTM E2736: Guide for Digital Detector Array Radiography.
• ASTM E2007: Guide for Computed Radiography.
• ASTM E2597: Practice for Manufacturing Characterization of Digital Detector Arrays.
• ASTM E1316: Terminology for Nondestructive Examinations.

These related documents provide critical context and supplementary procedures for effective application of digital neutron radiography and further enhancement of image quality assessment techniques.

---

Keywords: digital neutron radiography, ASTM E3398, nondestructive testing, imaging plate, digital detector array, computed radiography, camera-based system, neutron imaging, industrial radiography, tomography, image quality.

Standards Content (Sample)

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: E3398 − 23
Standard Guide for
Digital Neutron Radiography
This standard is issued under the fixed designation E3398; 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 E748 Guide for Thermal Neutron Radiography of Materials
E803 Test Method for Determining the L/D Ratio of Neutron
1.1 This guide covers the evaluation, qualification, and
Radiography Beams
quantification of digital neutron images. These images can be
E1316 Terminology for Nondestructive Examinations
acquired by many methods, including: neutron sensitive imag-
E1647 Practice for Determining Contrast Sensitivity in Ra-
ing plates (Computed Radiography – CR), Digital Detector
diology
Arrays – DDA’s (amorphous silicon, CMOS, CCD, etc.),
E2007 Guide for Computed Radiography
micro-channel plates, neutron sensitive fluoroscopes, neutron
E2597 Practice for Manufacturing Characterization of Digi-
sensitive scintillators coupled to optical cameras, digitized
tal Detector Arrays
radiographic films, and linear diode arrays.
E2736 Guide for Digital Detector Array Radiography
1.2 This guide does not purport to establish what is consid-
E2861 Test Method for Measurement of Beam Divergence
ered an acceptable image but is intended to only give guidance
and Alignment in Neutron Radiologic Beams
on digital neutron imaging, as well as image quality metrics of
importance, and how they can be measured and reported.
3. Terminology
1.3 The values stated in SI units are to be regarded as
3.1 Definitions—For definitions of terms used in these
standard. No other units of measurement are included in this
practices, see Terminology E1316, Section H.
standard.
4. Significance and Use
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 4.1 Purpose—Practices to be employed for the radiographic
examination of materials and components with neutrons using
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter- digital neutron detectors are outlined herein. They are intended
as a guide for the assessment of a digital neutron radiograph’s
mine the applicability of regulatory limitations prior to use.
1.5 This international standard was developed in accor- characteristics. For information on neutron beam lines for
dance with internationally recognized principles on standard- imaging and film neutron radiography, refer to Guide E748.
ization established in the Decision on Principles for the
4.2 Limitations—Acceptance standards have not been estab-
Development of International Standards, Guides and Recom-
lished for any material or production process. Neutron
mendations issued by the World Trade Organization Technical
radiography, whether performed by means of a reactor, an
Barriers to Trade (TBT) Committee.
accelerator, subcritical assembly, or radioactive source, will be
consistent in sensitivity and spatial resolution only if the
2. Referenced Documents
consistency of all details of the technique, such as neutron
2.1 ASTM Standards:
source, collimation, geometry, imaging system, etc., are main-
E94 Guide for Radiographic Examination Using Industrial
tained. This guide is limited to the use of digital neutron
Radiographic Film
detectors in combination with neutron conversion materials for
E545 Test Method for Determining Image Quality in Direct
image recording. This guide is intended for use with thermal
Thermal Neutron Radiographic Examination
and cold neutron spectrums. The production of thermal neutron
radiographs by employing the use of film and appropriate
conversion screens is covered in Guide E748.
This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-
tive Testing and is the direct responsibility of Subcommittee E07.05 on Radiology
4.3 Interpretation and Acceptance Standards—Interpretat-
(Neutron) Method.
ion and acceptance standards are not covered by this guide.
Current edition approved July 1, 2023. Published July 2023. DOI: 10.1520/
Designation of accept-reject standards is recognized to be
E3398-23
For referenced ASTM standards, visit the ASTM website, www.astm.org, or within the cognizance of product specifications.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
4.4 Other Aspects of the Neutron Radiographic Process—
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. For many important aspects of neutron radiography such as
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E3398 − 23
technique, files, viewing of radiographs, storage of 5.4 Though there are numerous methods that can be used to
radiographs, film processing, and record keeping, refer to produce digital neutron images, two methods are used com-
Guide E94, which covers these aspects for X-ray radiography. monly; these are Computed Radiography and Camera-Based
(See Section 2.) systems.
5.5 Computed Radiography (CR) Systems:
TEST METHODS
5.5.1 For general information on CR systems, refer to Guide
5. Background E2007. Only elements unique to neutron CR (nCR) are
discussed here.
5.1 Neutron radiography in industry has been performed
5.5.2 X-ray CR (XCR) and nCR are fundamentally the same
predominately using single emulsion X-ray film and gado-
process, except that nCR includes the use of a neutron
linium conversion screens using the direct method. The devel-
converter. Neutrons are not directly detectable by any reaction,
opment of standards may allow applications to move to digital
and therefore must be converted to some other particle that is
neutron imaging methods. There are some drawbacks to using
detectable, such as ionizing radiation (for example, beta
digital neutron imaging, such as the typically smaller field of
particles, gamma-rays). The storage phosphor and scanner are
view, high cost per detector, and the difficulty to simultane-
the same for both XCR and nCR.
ously achieve a high spatial resolution and a large field of view.
5.5.3 X-ray CR imaging plates (IP) are not efficient at
However, digital neutron imaging offers many advantages over
detecting neutrons since they do not usually contain a signifi-
film methods. These include:
cant amount of a strong neutron absorber. To overcome this,
5.1.1 Shorter exposure times,
two approaches are utilized: (1) embedding a neutron converter
5.1.2 Expanded bit-depth (increased contrast and latitude),
in an imaging plate built specifically for neutron imaging, and
5.1.3 Post processing (artifact correction, normalization,
(2) pressing a neutron converter against the surface of an X-ray
and filtering),
imaging plate.
5.1.4 Digital files (transport, duplication, and storage),
5.5.4 A strong neutron absorber (for example, gadolinium
5.1.5 Possibility for higher spatial resolution (neutron
oxide, Gd O ) can be mixed into the imaging plate’s storage
2 3
microscopes, single-event imaging),
phosphor. By mixing the neutron absorber into the phosphor
5.1.6 Dynamic (time-resolved) imaging, layer, radiation emitted in any direction from the conversion
material can be recorded in the phosphor layer, which can
5.1.7 Ability to obtain 3D information via tomography, and
improve efficiency, shorten exposure times, and potentially
5.1.8 Advanced techniques such as phase contrast imaging,
increase spatial resolution. The disadvantage of using imaging
spin-polarized imaging, time-of-flight imaging, and Bragg-
plates with embedded conversion materials is they are not
edge imaging.
widely available, have high cost, and generally lack durability
5.2 Neutrons are neutral particles that are challenging to
compared to standard high-resolution X-ray imaging plates.
detect. As a result, to image with thermal neutrons, the
Since the imaging plate is flexible, a flexible cassette can be
neutrons are absorbed (or scattered) to produce some other
used to allow imaging on a curved surface with reduced
form of radiation that is more easily detected. With film
geometric unsharpness.
imaging, a thin layer of a strong neutron absorber (such as
5.5.5 The second approach that can be utilized is to press a
gadolinium, boron, or indium) is generally employed to con-
thin layer of a neutron converter (often 25 μm of gadolinium on
vert neutrons into radiation that can expose the film (such as
an aluminum back plate) to the surface of an X-ray imaging
electrons and photons). Similarly, most approaches used for
plate, just like film neutron radiography. This approach allows
digital X-ray imaging can be used to produce images from
the use of X-ray imaging plates and potentially the conversion
neutrons with the use of a suitable material to convert neutrons
screens and cassettes utilized for film neutron radiography.
into a more detectable radiation. After this neutron conversion
This approach has several limitations. Firstly, with the conver-
process, the image recording, advantages, and disadvantages
sion screen on the surface, not more than half of the emissions
for producing images will be similar to those of X-ray imaging
from the conversion screen will be traveling towards the IP,
with the same method. However, the neutron conversion
limiting conversion efficiency. Secondly, the conversion screen
process and the presence of multiple types of radiation add
is normally placed behind the CR IP. As a result, the neutrons
other factors that will affect the image.
pass through the IP before reaching the conversion screen.
Since the IP is reasonably thick and hydrogenous this results in
5.3 Neutron imaging setups always have some gamma
some neutron scattering.
content as a result of neutron production and subsequent
neutron interactions, as is discussed in Guide E748. The effect 5.5.6 Spatial resolution of nCR is limited by several factors,
of this gamma radiation should be considered specifically with including:
relation to the image acquisition method. In some cases, it may (1) The laser spot size, laser power, pixel pitch, and raster
be possible for a digital imaging system to establish which rate of the scanner,
detections are the result of gamma radiation and which are (2) Light diffusion in the imaging plate phosphor layer, and
from neutrons, and so ignore the gamma detections. These (3) Thickness of the phosphor layer, and other factors that
systems, however, have too slow of count rates for practical affect spatial resolution in all CR systems. If a neutron absorber
imaging applications currently. is added to the phosphor layer it may affect the light spread.
E3398 − 23
Additionally, there is lost spatial resolution in the neutron period of time as the converter decays. Imaging plates are more
conversion process as the neutron’s original position is not sensitive than film, so shorter transfer times are often employed
recorded by the imaging plate but rather the detection location compared to transfer method with film.
of the conversion radiation emitted by the neutron absorber as
5.6 Camera-Based System (CBS):
the radiation traverses the phosphor layer. Generally, a basic
5.6.1 For general information on DDA systems refer to
spatial resolution of around 100 μm is obtainable by using a
Guide E2736. Only elements unique to neutron imaging with
high-resolution IP with a thin conversion screen (for example,
such systems are discussed here. A CBS consists of a neutron-
25 μm gadolinium on an aluminum substrate).
sensitive scintillator screen, a digital camera, and optics that
5.5.7 Contrast in nCR is driven by the attenuation charac-
couple the camera to the scintillator screen. The scintillator
teristics of neutrons in the object, for which behavior can be
screen contains a neutron converter material that absorbs
very different and complementary compared to X-rays.
incident neutrons and releases ionizing radiation. The second-
5.5.8 Field of View, imaging plates and scanners for XCR
ary radiation interacts with the surrounding scintillator material
are widely available in the common film sizes, allowing a
to emit visible light, which is then recorded by the digital
reasonably large field of view compared to other digital
camera. Fig. 1 depicts a typical system. The resulting image
methods. Smaller formats are also widely available.
quality is affected by numerous factors including the material
5.5.9 Counting statistics are affected by the flux and expo-
absorbing the neutron, the thickness of the scintillation screen,
sure time as with other digital methods. Film generally requires
the optics between the scintillation screen and the camera, and
9 2
a fluence of around 10 neutrons per cm when using a
the camera system.
gadolinium conversion screen. nCR could produce an image
5.6.2 The scintillation screens utilized need to have a
with similar contrast sensitivity in nearly half the fluence.
sufficiently high probability of detecting neutrons, produce a
Generally, the exposure time would be of the same order of
suitable quantity of light, and adequately maintain the position
magnitude as for film imaging. Typically, the longer the
of the incident neutron. Several suitable materials are com-
exposure the better the image until the IP becomes saturated.
monly used: gadolinium oxysulfide Gd O S(Tb) (Gadox),
2 2
5.5.10 X-ray CR imaging plate phosphors are designed for
lithium-6 fluoride zinc sulfide (ZnS/ LiF), and boron-10 oxide
X-ray imaging, and thus contain high-Z materials for high
zinc sulfide ( B O /ZnS).
2 3
X-ray attenuation. As a result, gamma-rays typically represent
5.6.3 These neutron scintillator screens contain a conver-
a significant portion of the recorded image, reducing contrast,
sion material to absorb neutrons and subsequently emit sec-
and complicating the interpretation of the image.
ondary decay radiation which can be detected more easily. The
5.5.11 The lifetime of imaging plates is generally limited by
secondary radiation (usually electrons or alpha particles) then
physical damage to the phosphor surface of the plate. Some
interacts with the scintillator that emits visible light. The higher
damage occurs during the scanning process from imaging plate
the neutron absorption cross section for the converter material,
feeding as well as from physical handling of the imaging plate.
the more efficient the detector will be, which allows for shorter
Damage usually takes the form of scratches which are visible
exposure times, improved counting statistics, and can indi-
on the resulting digital images. Generally, plates are expected
rectly improve spatial resolution by allowing the use of thinner
to last hundreds of uses, and potentially thousands for X-ray
scintillation screens. Having a thicker scintillation screen can
imaging plates.
increase the neutron detection efficiency and the light output.
5.5.12 Plastic (X-ray) cassettes are readily available for
However, as the light travels through the scintillation screen, it
imaging plates, but plastic will scatter a large number of
diffuses in the scintillator, diminishing spatial resolution.
neutrons and significantly reduce the spatial resolution. Alu-
Additionally, some light will be attenuated as it passes through
minum or magnesium alloy film cassettes should be utilized. If
the scintillation screen. As a general guideline, the scintillation
using a conversion screen with an X-ray imaging plate, the
screen thickness should not vastly exceed the imaging system’s
cassette needs to ensure intimate contact with the conversion
target basic spatial resolution, with scintillation screens be-
screen.
tween 20 μm and 100 μm in thickness being common.
5.5.13 While direct nCR uses a converter material (for
5.6.4 Gadox can be used in higher spatial resolution imag-
example, gadolinium) that emits radiation promptly upon
ing setups as a result of gadolinium’s large neutron absorption
absorption of a neutron, the indirect, or transfer, method uses a
cross section for thermal neutrons and to a lesser extent, the
converter material (for example, indium or dysprosium) that
range of the electrons emitted on neutron absorption, which is
absorbs a neutron, becomes radioactive, and emits its conver-
about 5 μm to 10 μm. A basic spatial resolution of around
sion radiation over a period of time. The transfer method can be
30 μm is achievable with a 20 μm thick scintillator.
employed by activating a separate conversion screen or em-
5.6.5 In scintillation screens containing lithium, neutron
bedded material in the neutron beam before producing the
image on the plate. If using an embedded neutron converter, absorption in the lithium-6 isotope results in the emission of an
the screen should be cleared using the CR scanner following alpha and a triton of relatively high energy (4.78 MeV total).
activation and prior to recording the transfer image. If using a As a result, these particles can travel further and so can emit
separate conversion screen, the imaging plate is not exposed to light at a greater distance from the incident neutron. Basic
the neutron beam line and instead the activated transfer screen spatial resolution around 50 μm can be achieved with a 100 μm
is placed in contact with the imaging plate in a cassette outside thick scintillator. These ZnS/ LiF scintillator screens typically
of the beam to record the image on the imaging plate over a emit substantially more light than Gadox scintillator screens.
E3398 − 23
FIG. 1 General Layout for a CBS
5.6.6 Scintillator screens are also sensitive to gamma 5.6.8 The cameras used are most commonly black and white
exposure, which will similarly produce light that will be CCD or CMOS digital cameras. These are usually either
included in the image. In many cases the signal produced by produced for astronomy or other scientific applications. The
these gamma interactions may locally significantly exceed that resulting image is limited to the number of pixels present in the
of the
...