1、Designation: E748 02 (Reapproved 2008)E748 16Standard PracticesGuide forThermal Neutron Radiography of Materials1This standard is issued under the fixed designation E748; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of
2、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. Scope Scope*1.1 PurposePractices to be employed for the radiographic examination of materials and components with thermal neutr
3、onsare outlined herein. They are intended as a guide for the production of neutron radiographs that possess consistent qualitycharacteristics, as well as aiding the user to consider the applicability of thermal neutron radiology (radiology, radiographic, andrelated terms are defined in Terminology r
4、adiology. E1316). Statements concerning preferred practice are provided without adiscussion of the technical background for the preference. The necessary technical background can be found in Refs (1-16).21.2 LimitationsAcceptance standards have not been established for any material or production pro
5、cess (see Section 5 on BasisofApplication).Adherence to the practicesguide will, however, produce reproducible results that could serve as standards. results.Neutron radiography, whether performed by means of a reactor, an accelerator, subcritical assembly, or radioactive source, will beconsistent i
6、n sensitivity and resolution only if the consistency of all details of the technique, such as neutron source, collimation,geometry, film, etc., is maintained through the practices. These practices are are maintained. This guide is limited to the use ofphotographic or radiographic film in combination
7、 with conversion screens for image recording; other imaging systems areavailable. Emphasis is placed on the use of nuclear reactor neutron sources.1.3 Interpretation and Acceptance StandardsInterpretation and acceptance standards are not covered by these practices.thisguide. Designation of accept-re
8、ject standards is recognized to be within the cognizance of product specifications.1.4 Safety PracticesGeneral practices for personnel protection against neutron and associated radiation peculiar to the neutronradiologic process are discussed in Section 17. For further information on this important
9、aspect of neutron radiology, refer tocurrent documents of the National Committee on Radiation Protection and Measurement, the Code of Federal Regulations, the U.S.Nuclear Regulatory Commission, the U.S. Department of Energy, the National Institute of Standards and Technology, and toapplicable state
10、and local codes.Jurisdictional nuclear regulations will also apply.1.5 Other Aspects of the Neutron Radiographic ProcessFor 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.
11、, which covers theseaspects for x-ray radiography. (See Section 2.)1.6 The values stated in either SI or inch-pound units are to be regarded as the standard.1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user
12、of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.(For more specific safety information see 1.4.)2. Referenced Documents2.1 ASTM Standards:3E94 Guide for Radiographic ExaminationE543 Specification for Agencies
13、Performing Nondestructive TestingE545 Test Method for Determining Image Quality in Direct Thermal Neutron Radiographic ExaminationE803 Test Method for Determining the L/D Ratio of Neutron Radiography BeamsE1316 Terminology for Nondestructive Examinations1 These practices are under the jurisdiction o
14、f ASTM Committee E07 on Nondestructive Testing and are the direct responsibility of Subcommittee E07.05 on Radiology(Neutron) Method.Current edition approved July 1, 2008Feb. 15, 2016. Published September 2008February 2016. Originally approved in 1980. Last previous edition approved in 20022008as E7
15、48 02.E748 02(2008). DOI: 10.1520/E0748-02R08.10.1520/E0748-16.2 The boldface numbers in parentheses refer to the list of references at the end of these practices.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book
16、of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.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 technica
17、lly possible to adequately depict all changes accurately, ASTM recommends that users 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.*A Summary of Changes section appears at the end of this sta
18、ndardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1E1496 Test Method for Neutron Radiographic Dimensional Measurements (Withdrawn 2012)42.2 ASNT Standard:Recommended Practice SNT-TC-1A for Personnel Qualification and Certification42
19、.3 ANSI Standard:ANSI/ASNT-CP-189 Standard for Qualification and Certification of Nondestructive Testing Personnel52.4 AIA Document:NAS-410 Nondestructive Testing Personnel Qualification and Certification62.5 ISO Standard:ISO 9712 Non-Destructive TestingQualification and Certification of NDT Personn
20、el73. Terminology3.1 DefinitionsFor definitions of terms used in these practices, see Terminology E1316, Section H.3.1 DefinitionsFor definitions of terms used in these practices, see Terminology E1316, Section H.4. Significance and Use4.1 These practices includeThis guide covers types of materials
21、to be examined, neutron radiographic examination techniques,neutron production and collimation methods, radiographic film, and converter screen selection. Within the present state of theneutron radiologic art, these practices are generally applicable to specific material combinations, processes, and
22、 techniques.5. Basis of Application5.1 Personnel QualificationNondestructive testing (NDT) personnel If specified in the contractual agreement, personnelperforming examinations to this standard shall be qualified in accordance with a nationally or internationally recognized NDTpersonnel qualificatio
23、n practice or standard such as ANSI/ASNT-CP-189, SNT-TC-1A, NAS-410, ISO 9712, or a similardocument. document and certified by the employer or certifying agency, as applicable. The practice or standard used and itsapplicable revision shall be specifiedidentified in the contractual agreement between
24、the using parties.5.2 Qualification of Nondestructive AgenciesIf specified in the contractual agreement, NDT agencies shall be qualified andevaluated as described in Practice E543. The applicable edition of Practice E543 shall be specified in the contractual agreement.5.3 Procedures and TechniquesTh
25、e procedures and techniques to be used shall be as described in these practices unlessotherwise specified. Specific techniques may be specified in the contractual agreement.5.4 Extent of ExaminationThe extent of examination shall be in accordance with Section 16 unless otherwise specified.5.4 Report
26、ing Criteria/Acceptance CriteriaReporting criteria for the examination results shall be in accordance with 1.3unless otherwise specified. Acceptance criteria (for example, for reference radiographs) shall be specified in the contractualagreement.5.6 Reexamination of Repaired/Reworked ItemsReexaminat
27、ion of repaired/reworked items is not addressed in these practicesand, if required, shall be specified in the contractual agreement.6. Neutron Radiography6.1 The MethodNeutron radiography is basically similar to XX-ray radiography in that both techniques employ radiationbeam intensity modulation by
28、an object to image macroscopic object details. X rays X-rays or gamma rays are replaced by neutronsas the penetrating radiation in a through-transmission examination. Since the absorption characteristics of matter for X rays X-raysand neutrons differ drastically, the two techniques in general serve
29、to complement one another.6.2 FacilitiesThe basic neutron radiography facility consists of a source of fast neutrons, a moderator, a gamma filter, acollimator, a conversion screen, a film image recorder or other imaging system, a cassette, and adequate biological shielding andinterlock systems. A sc
30、hematic diagram of a representative neutron radiography facility is illustrated in Fig. 1.6.3 ThermalizationThe process of slowing down neutrons by permitting the neutrons to come to thermal equilibrium withtheir surroundings; see definition of thermal neutrons in Terminology E1316, Section H.7. Neu
31、tron Sources7.1 GeneralThe thermal neutron beam may be obtained from a nuclear reactor, a subcritical assembly, a radioactive neutronsource, or an accelerator. Neutron radiography has been achieved successfully with all four sources. In all cases the initial neutronsgenerated possess high energies a
32、nd must be reduced in energy (moderated) to be useful for thermal neutron radiography. This may4 Available from the American Society for Nondestructive Testing, 1711 Arlingate Lane, P.O. Box 28518, Columbus, OH 43228-0518.5 Available from American National Standards Institute (ANSI), 25 W. 43rd St.,
33、 4th Floor, New York, NY 10036.6 Available from Aerospace Industries Association of America, Inc., 1250 Eye St., NW, Washington, DC 200057 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.E748 162be achieved by surrounding
34、 the source with light materials such as water, oil, plastic, paraffin, beryllium, or graphite. The preferredmoderator will be dependent on the constraints dictated by the energy of the primary neutrons, which will in turn be dictated byneutron beam parameters such as thermal neutron yield requireme
35、nts, cadmium ratio, and beam gamma ray contamination. Thecharacteristics of a particular system for a given application are left for the seller and the buyer of the service to decide.Characteristics and capabilities of each type of source are referenced in the References section. A general compariso
36、n of sourcesis shown in Table 1.7.2 Nuclear ReactorsNuclear reactors are the preferred thermal neutron source in general, since high neutron fluxes areavailable and exposures can be made in a relatively short time span. The high neutron intensity makes it possible to provide atightly collimated beam
37、; therefore, high-resolution radiographs can be produced.7.3 Subcritical AssemblyA subcritical assembly is achieved by the addition of sufficient fissionable material surrounding amoderated source of neutrons, usually a radioisotope source. Although the total thermal neutron yield is smaller than th
38、at of anuclear reactor, such a system offers the attractions of adequate image quality in a reasonable exposure time, relative ease oflicensing, adequate neutron yield for most industrial applications, and the possibility of transportable operation.7.4 Accelerator SourcesAccelerators used for therma
39、l neutron radiography have generally been of the low-voltage type whichutilize the 3H(d,n)4He reaction, high-energy X-ray machines in which the (x,n) reaction is applied and Van de Graaff and otherhigh-energy accelerators which employ reactions such as 9Be(d,n)10B. In all cases, the targets are surr
40、ounded by a moderator toreduce the neutrons to thermal energies. The total neutron yields of such machines can be on the order of 1012ns1; the thermalneutron flux of such sources before collimation can be on the order of 109ncm2s1, for example, the yield from a Van de Graaffaccelerator.7.5 Isotopic
41、SourcesMany isotopic sources have been employed for neutron radiologic applications. Those that have beenmost widely utilized are outlined in Table 2. Radioactive sources offer the best possibility for portable operation. However, becauseof the relatively low neutron yield, the exposure times are us
42、ually long for a given image quality. The isotopic source 252Cf offersa number of advantages for thermal neutron radiology, namely, low neutron energy and small physical size, both of which leadto efficient neutron moderation, and the possibility for high total neutron yields.8. Imaging Methods and
43、Conversion Screens8.1 GeneralNeutrons are nonionizing indirectly ionizing particulate radiation that have little direct effect on radiographic film.To obtain a neutron radiographic image on film, a conversion screen is normally employed; upon neutron capture, screens emitprompt and delayed decay pro
44、ducts in the form of nuclear radiation or light. In all cases the screen should be placed in intimatecontact with the radiographic film in order to obtain sharp images.8.2 Direct MethodIn the direct method, a film is placed on the source side of the conversion screen (front film) and exposedto the n
45、eutron beam together with the conversion screen. Electron emission upon neutron capture is the mechanism by which thefilm is primarily exposed in the case of gadolinium conversion screens. The screen is generally one of the following types: (1) afree-standing gadolinium metal screen accessible to fi
46、lm on both sides; (2) a sapphire-coated, vapor-deposited gadolinium screenon a substrate such as aluminum; or (3) a light-emitting fluorescent screen such as gadolinium oxysulfide or 6LiF/ZnS. ExposureFIG. 1 Typical Neutron Radiography Facility with Divergent CollimatorTABLE 1 Comparison of Thermal
47、Neutron SourcesType of Source Typical Radiographic Flux, n/cm2s Radiographic Resolution CharacteristicsNuclear reactor 105 to 108 excellent stable operation, not portableSubcritical assembly 104 to 106 good stable operation, portability difficultAccelerator 103 to 106 medium on-off operation, transp
48、ortableRadioisotope 101 to 104 poor to medium stable operation, portability possibleE748 163of an additional film (without object) is often useful to resolve artifacts that may appear in radiographs. Such artifacts could resultfrom screen marks, excess pressure, light leaks, development, or nonunifo
49、rmnon-uniform film. In the case of light-emittingconversion screens, it is recommended that the spectral response of the light emission be matched as closely as possible to thatof the film used for optimum results. The direct method should be employed whenever high-resolution radiographs are required,and high beam contamination of low-energy gamma rays or highly radioactive objects do not preclude its use.8.3 Indirect MethodThis method makes use of conversion screens that can be made temporarily radioactive by neutroncapture. The conversion sc
