ASTM E1000-1998(2003) Standard Guide for Radioscopy《射线检验法》.pdf

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1、Designation: E 1000 98 (Reapproved 2003)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 (e) 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-s

3、uring 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 inf

5、ormation 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 regu

6、latory limitations prior to use. For specific safetyprecautionary statements, see Section 6.2. Referenced Documents2.1 ASTM Standards:E 142 Method for Controlling Quality of RadiographicTesting2E 747 Practice for Design, Manufacture and MaterialGrouping Classification of Wire Image Quality Indicator

7、s(IQI) Used for Radiology2E 1025 Practice for Design, Manufacture, and MaterialGrouping Classification of Hole-Type Image Quality Indi-cators (IQI) Used for Radiology2E 1316 Terminology for Nondestructive Examinations2E 2002 Practice for Determining Total Image Unsharpnessin Radiology22.2 National C

8、ouncil 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 MeV3NCRP 51 Radiation Protection Design Guidelines for0.1100 MeV Particle Accelerator Facilities3NCRP 91, (supercedes NCRP 3

9、9) Recommendations onLimits for Exposure to Ionizing Radiation32.3 Federal Standard:Fed. Std. No. 21-CFR 1020.40 Safety Requirements forCabinet X-Ray Machines43. Summary of Guide3.1 This guide outlines the practices for the use of radio-scopic methods and techniques for materials examinations. It is

10、intended 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 nonde

11、structive 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

12、 a mechanism. 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 b

13、e further employed to checkthe functioning of internal mechanisms. Radioscopy permitstimely assessments of product integrity, and allows promptdisposition of the product based on acceptance standards.Although closely related to the radiographic method, it hasmuch lower operating costs in terms of ti

14、me, manpower, andmaterial.4.2 Long-term records of the radioscopic image may beobtained through motion-picture recording (cinefluorography),1This 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 an

15、d Gamma) Method.Current edition approved March 10, 2003. Published May 2003. Originallyapproved in 1989. Last previous edition approved in 1998 as E 1000 - 98.2Annual Book of ASTM Standards, Vol 03.03.3Available from NCRP Publications, 7010 Woodmont Ave., Suite 1016, Be-thesda, MD 20814.4Available f

16、rom Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.video recording, or “still” photographs using conventionalcameras.

17、 The radioscopic image may be electronically en-hanced, digitized, or otherwise processed 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

18、 the development of more powerful radiation sources andimproved screens. Fluoroscopic screens 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 phosphorc

19、oating. Screen brightness is also a function of the wavelengthof the impinging radiation. 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 scree

20、nslimited the industrial applications of fluoroscopy. The lightoutput of suitable screens 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

21、 to beviewed through leaded glass or indirectly using mirror optics.Such systems were used 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 cho

22、ice offluoroscopy over radiography was generally justified wheretime and cost factors were 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-

23、ray image intensifierprovided the greatest impetus. It had sufficient brightness gainto bring 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 t

24、he X rays to light, aphotocathode (in intimate contact with the input phosphor) toconvert 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 t

25、he energy imparted tothe electrons. Early units had brightness gains of around 1200to 1500 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

26、, welds in steelthicknesses up to 28.6 mm 1.125 in. can be examined at 2 %plaque penetrameter 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

27、 low-densitymaterials were marketed. Because they require a comparativelyhigh X-ray flux 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) c

28、ameratubes, such as the isocon, intensifier orthicon, and secondaryelectron conduction (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 result

29、s are com-parable to those obtained with the image intensifier.5.3 In recent years (circa 1980s) new digital radiologytechniques have been developed. These methods producedirectly digitized representations of the X-ray field transmittedby an examination article. Direct digitization enhances thesigna

30、l-to-noise ratio of the data and presents the information ina form directly suitable for 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

31、arrangements.5.4 All of these techniques employ television presentationand can utilize various 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 versa

32、tilityof radioscopic imaging. Industrial applications have becomewide-spread: production 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

33、and reinforcedplastics are typical examples.5.5 LimitationsDespite the numerous advances 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

34、 control of scatter, and the use ofscreens make it relatively simple to obtain better than 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-

35、handling considerations in a dynamicimaging system mandate that the image plane be separatedfrom 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

36、 contrary to the need for thehigh X-ray flux density cited previously. Furthermore, limita-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, sub

37、ject, and detector and oftenexpensive product-handling mechanisms. These, along withthe radiation safety requirements peculiar to dynamic systemsusually result in capital equipment costs considerably in excessof that for conventional radiography. The costs of expendables,manpower, product-handling a

38、nd time, however, are usuallysignificantly lower for radioscopic systems.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

39、 of radiation are available inE 1000 98 (2003)2publications such as the Fed. Std. No. 21-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. I

40、nterpretation and Reference Standards7.1 Reference radiographs produced by ASTM and accep-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 fluorosc

41、opic images.8. Radioscopic Devices, Classification8.1 The most commonly used electromagnetic 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. T

42、he detection of these X-ray photons in such a waythat the information they carry can be 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 fewdeserv

43、e more than the attention caused by scientific curiosity.For our purposes here, only these 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 electro

44、n conversion.8.3 X Ray to Light ConversionRadioscopic SystemsInthese systems X-ray photons 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 w

45、henexcited by X-ray photons. Those used most commonly are asfollows:8.3.1 PhosphorsThese 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,

46、and calcium tungstate are in common use. Coating weightsvary from approximately 50 mg/cm2to 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

47、 light whose brightness is proportional to theenergy of the photon. Since the materials 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 (th

48、allium-activated) and sodium iodide (cesium-activated). These single crystal materials can 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 Ele

49、ctron 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 Energizing of Semiconductor JunctionsThe resis-tance of a semiconductor, or of a semiconductor junction in adevice such as a diode or transistor, can be altered by addingfree electrons. The energy of an X-ray photon i