ASTM E1000-1998(2009) 752 Standard Guide for Radioscopy《射线的标准指南》.pdf

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1、Designation: E 1000 98 (Reapproved 2009)Standard Guide forRadioscopy1This standard is issued under the fixed designation E 1000; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses ind

2、icates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide is for tutorial purposes only and to outline thegeneral principles of radioscopic imaging.1.2 This guide describes practices and image quality mea-su

3、ring systems for real-time, and near real-time, nonfilmdetection, display, and recording of radioscopic images. Theseimages, used in materials examination, are generated bypenetrating radiation passing through the subject material andproducing an image on the detecting medium. Although thedescribed

4、radiation sources are specifically X-ray and gamma-ray, the general concepts can be used for other radiationsources such as neutrons. The image detection and displaytechniques are nonfilm, but the use of photographic film as ameans for permanent recording of the image is not precluded.NOTE 1For info

5、rmation purposes, refer to Terminology E 1316.1.3 This standard does not purport to address all of thesafety concerns, if any, associated 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 regul

6、atory limitations prior to use. For specific safetyprecautionary statements, see Section 6.2. Referenced Documents2.1 ASTM Standards:2E 142 Method for Controlling Quality of RadiographicTesting3E 747 Practice for Design, Manufacture and MaterialGrouping Classification of Wire Image Quality Indicator

7、s(IQI) Used for RadiologyE 1025 Practice for Design, Manufacture, and MaterialGrouping Classification of Hole-Type Image Quality Indi-cators (IQI) Used for RadiologyE 1316 Terminology for Nondestructive ExaminationsE 2002 Practice for Determining Total Image Unsharpnessin Radiology2.2 National Counc

8、il on Radiation Protection and Mea-surement (NCRP) Standards:NCRP 49 Structural Shielding Design and Evaluation forMedical Use of X Rays and Gamma Rays of Energies upto 10 MeV4NCRP 51 Radiation Protection Design Guidelines for0.1100 MeV Particle Accelerator Facilities4NCRP 91, (supercedes NCRP 39) R

9、ecommendations onLimits for Exposure to Ionizing Radiation42.3 Federal Standard:Fed. Std. No. 21-CFR 1020.40 Safety Requirements forCabinet X-Ray Machines53. Summary of Guide3.1 This guide outlines the practices for the use of radio-scopic methods and techniques for materials examinations. It isinte

10、nded to provide a basic understanding of the method andthe techniques involved. The selection of an imaging device,radiation source, and radiological and optical techniques toachieve a specified quality in radioscopic images is described.4. Significance and Use4.1 Radioscopy is a versatile nondestru

11、ctive means forexamining an object. It provides immediate information re-garding the nature, size, location, and distribution of imperfec-tions, both internal and external. It also provides a rapid checkof the dimensions, mechanical configuration, and the presenceand positioning of components in a m

12、echanism. It indicates inreal-time the presence of structural or component imperfec-tions anywhere in a mechanism or an assembly. Throughmanipulation, it may provide three-dimensional informationregarding the nature, sizes, and relative positioning of items ofinterest within an object, and can be fu

13、rther employed to checkthe functioning of internal mechanisms. Radioscopy permitstimely assessments of product integrity, and allows prompt1This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-tive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology(X and

14、 Gamma) Method.Current edition approved June 1, 2009. Published July 2009. Originally approvedin 1989. Last previous edition approved in 2003 as E 1000 - 98 (2003).2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Boo

15、k of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4Available from NCRP Publications, 7010 Woodmont Ave., Suite 1016, Be-thesda, MD 20814.5Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelp

16、hia, PA 19111-5094, Attn: NPODS.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.disposition of the product based on acceptance standards.Although closely related to the radiographic method, it hasmuch lower operating costs in terms o

17、f time, manpower, andmaterial.4.2 Long-term records of the radioscopic image may beobtained through motion-picture recording (cinefluorography),video recording, or “still” photographs using conventionalcameras. The radioscopic image may be electronically en-hanced, digitized, or otherwise processed

18、for improved visualimage analysis or automatic, computer-aided analysis, or both.5. Background5.1 Fluorescence was the means by which X rays werediscovered, but industrial fluoroscopy began some years laterwith the development of more powerful radiation sources andimproved screens. Fluoroscopic scre

19、ens typically consist ofphosphors that are deposited on a substrate. They emit light inproportion to incident radiation intensity, and as a function ofthe composition, thickness, and grain size of the phosphorcoating. Screen brightness is also a function of the wavelengthof the impinging radiation.

20、Screens with coarse-grained orthick coatings of phosphor, or both, are usually brighter buthave lower resolution than those with fine grains or thincoatings, or both. In the past, conventional fluorescent screenslimited the industrial applications of fluoroscopy. The lightoutput of suitable screens

21、was quite low (on the order of 0.1millilambert or 0.343 3 103cd/m2) and required about 30 minfor an examiner to adapt his eyes to the dim image. To protectthe examiner from radiation, the fluoroscopic image had to beviewed through leaded glass or indirectly using mirror optics.Such systems were used

22、 primarily for the examination oflight-alloy castings, the detection of foreign material in food-stuffs, cotton and wool, package inspection, and checkingweldments in thin or low-density metal sections. The choice offluoroscopy over radiography was generally justified wheretime and cost factors were

23、 important and other nondestructivemethods were not feasible.5.2 It was not until the early 1950s that technologicaladvances set the stage for widespread uses of industrialfluoroscopy. The development of the X-ray image intensifierprovided the greatest impetus. It had sufficient brightness gainto br

24、ing fluoroscopic images to levels where examination couldbe performed in rooms with somewhat subdued lighting, andwithout the need for dark adaption. These intensifiers con-tained an input phosphor to convert the X rays to light, aphotocathode (in intimate contact with the input phosphor) toconvert

25、the light image into an electronic image, electronaccelerating and focusing electrodes, and a small outputphosphor. Intensifier brightness gain results from both the ratioof input to output phosphor areas and the energy imparted tothe electrons. Early units had brightness gains of around 1200to 1500

26、 and resolutions somewhat less than high-resolutionconventional screens. Modern units utilizing improved phos-phors and electronics have brightness gains in excess of10 0003 and improved resolution. For example, welds in steelthicknesses up to 28.6 mm (1.125 in.) can be examined at 2 %plaque penetra

27、meter sensitivity using a 160 constant potentialX-ray generator (keVcp) source. Concurrent with image-intensifier developments, direct X ray to television-cameratubes capable of high sensitivity and resolution on low-densitymaterials were marketed. Because they require a comparativelyhigh X-ray flux

28、 input for proper operation, however, their usehas been limited to examination of low-density electroniccomponents, circuit boards, and similar applications. Thedevelopment of low-light level television (LLLTV) cameratubes, such as the isocon, intensifier orthicon, and secondaryelectron conduction (

29、SEC) vidicon, and the advent of ad-vanced, low-noise video circuitry have made it possible to usetelevision cameras to scan conventional, high-resolution, low-light-output fluorescent screens directly. The results are com-parable to those obtained with the image intensifier.5.3 In recent years (circ

30、a 1980s) new digital radiologytechniques have been developed. These methods producedirectly digitized representations of the X-ray field transmittedby an examination article. Direct digitization enhances thesignal-to-noise ratio of the data and presents the information ina form directly suitable for

31、 electronic image processing andenhancement, and storage on magnetic tape. Digital radio-scopic systems use scintillator-photodetector and phosphor-photodetector sensors in flying spot and fan beam-detectorarray arrangements.5.4 All of these techniques employ television presentationand can utilize v

32、arious electronic techniques for image en-hancement, image storage, and video recording. These ad-vanced imaging devices, along with modern video processingand analysis techniques, have greatly expanded the versatilityof radioscopic imaging. Industrial applications have becomewide-spread: production

33、 examination of the longitudinal fusionwelds in line pipe, welds in rocket-motor housings, castings,transistors, microcircuits, circuit-boards rocket propellant uni-formity, solenoid valves, fuses, relays, tires and reinforcedplastics are typical examples.5.5 LimitationsDespite the numerous advances

34、 in RRTItechnology, the sensitivity and resolution of real-time systemsusually are not as good as can be obtained with film. Inradiography the time exposures and close contact between thefilm and the subject, the control of scatter, and the use ofscreens make it relatively simple to obtain better th

35、an 2 %penetrameter sensitivity in most cases. Inherently, because ofstatistical limitations dynamic scenes require a higher X-rayflux level to develop a suitable image than static scenes. Inaddition, the product-handling considerations in a dynamicimaging system mandate that the image plane be separ

36、atedfrom the surface of the product resulting in perceptible imageunsharpness. Geometric unsharpness can be minimized byemploying small focal spot (fractions of a millimetre) X-raysources, but this requirement is contrary to the need for thehigh X-ray flux density cited previously. Furthermore, limi

37、ta-tions imposed by the dynamic system make control of scatterand geometry more difficult than in conventional radiographicsystems. Finally, dynamic radioscopic systems require carefulalignment of the source, subject, and detector and oftenexpensive product-handling mechanisms. These, along withthe

38、radiation safety requirements peculiar to dynamic systemsusually result in capital equipment costs considerably in excessof that for conventional radiography. The costs of expendables,E 1000 98 (2009)2manpower, product-handling and time, however, are usuallysignificantly lower for radioscopic system

39、s.6. Safety Precautions6.1 The safety procedures for the handling and use ofionizing radiation sources must be followed. Mandatory rulesand regulations are published by governmental licensing agen-cies, and guidelines for control of radiation are available inpublications such as the Fed. Std. No. 21

40、-CFR 1020.40.Careful radiation surveys should be made in accordance withregulations and codes and should be conducted in the exami-nation area as well as adjacent areas under all possibleoperating conditions.7. Interpretation and Reference Standards7.1 Reference radiographs produced by ASTM and acce

41、p-tance standards written by other organizations may be em-ployed for radioscopic examination as well as for radiography,provided appropriate adjustments are made to accommodatefor the differences in the fluoroscopic images.8. Radioscopic Devices, Classification8.1 The most commonly used electromagn

42、etic radiation inradioscopy is produced by X-ray sources. X rays are affected invarious modes and degrees by passage through matter. Thisprovides very useful information about the matter that has beentraversed. The detection of these X-ray photons in such a waythat the information they carry can be

43、used immediately is theprime requisite of radioscopy. Since there are many ways ofdetecting the presence of X rays, their energy and flux density,there are a number of possible systems. Of these, only a fewdeserve more than the attention caused by scientific curiosity.For our purposes here, only the

44、se few are classified anddescribed.8.2 Basic Classification of Radioscopic SystemsAll com-monly used systems depend on two basic processes fordetecting X-ray photons: X-ray to light conversion and X-rayto electron conversion.8.3 X Ray to Light ConversionRadioscopic SystemsInthese systems X-ray photo

45、ns are converted into visible lightphotons, which are then used in various ways to produceimages. The processes are fluorescence and scintillation. Cer-tain materials have the property of emitting visible light whenexcited by X-ray photons. Those used most commonly are asfollows:8.3.1 PhosphorsThese

46、 include the commonly used fluo-rescent screens, composed of relatively thin, uniform layers ofphosphor crystals spread upon a suitable support. Zinc cad-mium sulfide, gadolinium oxysulfide, lanthanum oxybromide,and calcium tungstate are in common use. Coating weightsvary from approximately 50 mg/cm

47、2to 100 mg/cm.28.3.2 ScintillatorsThese are materials which are transpar-ent and emit visible light when excited by X rays. The emissionoccurs very rapidly for each photon capture event, and consistsof a pulse of light whose brightness is proportional to theenergy of the photon. Since the materials

48、are transparent, theylend themselves to optical configurations not possible with thephosphors used in ordinary fluorescent screens. Typical mate-rials used are sodium iodide (thallium-activated), cesiumiodide (thallium-activated) and sodium iodide (cesium-activated). These single crystal materials c

49、an be obtained invery large sizes (up to 30-cm or 12-in. diameter is notuncommon) and can be machined into various sizes and shapesas required. Thickness of 2 to 100 mm (0.08 to 4 in.) arecustomary.8.4 X Ray to Electron ConversionRadioscopic SystemsX-ray photons of sufficient energy have the ability to releaseloosely bound electrons from the inner shells of atoms withwhich they collide. These photoelectrons have energies pro-portional to the original X-ray photon and can be utilized in avariety of ways to produce images, including the followinguseful processes.8.4.1 Energ