ASTM E1000-2016 3962 Standard Guide for Radioscopy《射线的标准指南》.pdf

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1、Designation: E1000 16Standard Guide forRadioscopy1This standard is issued under the fixed designation E1000; 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 indicates the year of l

2、ast 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-suring systems for rea

3、l-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 radiation sources ar

4、e 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 information purposes, re

5、fer to Terminology E1316.1.3 This guide summarizes the state of radioscopic technol-ogy prior to the advent of Digital Detector Arrays (DDAs),which may also be used for radioscopic imaging. For asummary of DDAs, see E2736, Standard Guide for DigitalDetector Array Radiology. It should be noted that s

6、omedetector configurations listed herein have similar foundationsto those described in Guide E2736.1.4 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 healt

7、h practices and determine the applica-bility of regulatory limitations prior to use. For specific safetyprecautionary statements, see Section 6.2. Referenced Documents2.1 ASTM Standards:2E747 Practice for Design, Manufacture and Material Group-ing Classification of Wire Image Quality Indicators (IQI

8、)Used for RadiologyE1025 Practice for Design, Manufacture, and MaterialGrouping Classification of Hole-Type Image Quality In-dicators (IQI) Used for RadiologyE1316 Terminology for Nondestructive ExaminationsE1742 Practice for Radiographic ExaminationE2002 Practice for Determining Total Image Unsharp

9、nessand Basic Spatial Resolution in Radiography and Radios-copyE2736 Guide for Digital Detector Array Radiology2.2 National Council on Radiation Protection and Measure-ment (NCRP) Standards:NCRP 49 Structural Shielding Design and Evaluation forMedical Use of X-rays and Gamma Rays of Energies upto 10

10、 MeV3NCRP 51 Radiation Protection Design Guidelines for0.1100 MeV Particle Accelerator Facilities3NCRP 91, (supercedes NCRP 39) Recommendations onLimits for Exposure to Ionizing Radiation32.3 Federal Standard:Fed. Std. No. 21-CFR 1020.40 Safety Requirements forCabinet X-Ray Machines42.4 Aerospace In

11、dustries Association Document:NAS 410 Certification thelimitation in spatial resolution will be the size of the focal spot,and in contrast-to-noise ratio, the available integration time forone resulting image. Furthermore, limitations imposed by thedynamic system make control of scatter and geometry

12、 moredifficult than in conventional radiographic systems. Finally,dynamic radioscopic systems require careful alignment of thesource, subject, and detector and often expensive product-handling mechanisms. These, along with the radiation safetyrequirements peculiar to dynamic systems usually result i

13、ncapital equipment costs considerably in excess of that forconventional film radiography. The costs of expendables,manpower, product-handling and time, however, are usuallysignificantly lower for radioscopic systems.6. Safety Precautions6.1 The safety procedures for the handling and use ofionizing r

14、adiation sources must be followed. Mandatory rulesand regulations are published by governmental licensingagencies, and guidelines for control of radiation are availablein publications such as the Fed. Std. No. 21-CFR 1020.40.Careful radiation surveys should be made in accordance withregulations and

15、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 accep-tance standards written by other organizations may be em-ployed for radioscopic examin

16、ation 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 electromagnetic radiation inradioscopy is produced by X-ray sources. X-rays are affectedin various

17、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 used immediately is theprime requisite of radioscopy. Since there are many ways ofdetect

18、ing 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 these few are classified anddescribed.8.2 Basic Classification of Radioscopic SystemsAll co

19、m-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 photons are converted into visible lightphotons, which are then used in various ways to produ

20、ceimages. 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 (see section 10.6.3.1 for additional discussion onimage intensifiers):8.3.1 PhosphorsThese include the commo

21、nly 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/cm2to 200 mg/cm.28.3

22、.2 ScintillatorsThese are materials which are transpar-ent and emit visible light when excited by X-rays. Theemission occurs very rapidly for each photon capture event,and consists of a pulse of light whose brightness is proportionalto the energy of the photon. Since the materials are transparent,th

23、ey lend themselves to optical configurations not possible withthe phosphors used in ordinary fluorescent screens. Typicalmaterials used are sodium iodide (thallium-activated), cesiumE1000 163iodide (thallium-activated) and sodium iodide (cesium-activated). These single crystal, transparent or transl

24、ucentceramic materials can be obtained in very large sizes (up to45-cm or 17-in. diameter is now possible) and can be machinedinto various sizes and shapes as required. Thicknesses of 0.1 to100 mm (0.08 to 4 in.) are customary.8.4 X-ray to Electron ConversionRadioscopic SystemsX-ray photons of suffi

25、cient 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.

26、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 is capable offreeing electrons in such materials and can profoundly affectthe oper

27、ation of the device. For example, a simple silicon“solar cell” connected to a microammeter will produce asubstantial current when exposed to an X-ray source.8.4.1.1 If an array of small semiconductor devices is ex-posed to an X-ray beam, and the performance of each device issampled, then an image ca

28、n be produced by a suitable displayof the data. Such arrays can be linear or two-dimensional.Linear arrays normally require relative motion between theobject and the array to produce a useful real-time image. Thechoice depends upon the application.8.4.2 Affecting Resistance of SemiconductorsOne tech

29、nol-ogy used for direct X-ray-to-electron device is the X-raysensitive vidicon camera tube. Here the target layer of thevidicon tube, and its support, are modified to have an improvedsensitivity to X-ray photons. The result is a change in conduc-tivity of the target layer corresponding to the patter

30、n of X-rayflux falling upon the tube, and this is directly transformed bythe scanning beam into a video signal which can be used in avariety of ways.8.4.2.1 Photoconductive materials that exhibit X-ray sensi-tivity include cadmium telluride (CdTe), zinc cadmium tellu-ride (CdZnTe), cadmium selenide,

31、 lead oxide, selenium, gal-lium arsenide, and silicon. Some of these have been used inX-ray sensitive TV camera tubes. Cadmium sulfide is com-monly used as an X-ray detector, but not usually for imageformation. Selenium, CdTe, and CdZnTe (CZT) have beenformed over thin film transistor (TFT) arrays,

32、and are read-outdirectly in solid state imaging devices. These later devices withsolid state read-out circuitry are more appropriately defined asDigital Detector Arrays (DDAs), see E2736. Whereas theformer devices where the direct converter is coupled withcamera tube technology are treated as radios

33、copic devices.8.4.3 Microchannel PlatesThese consist of an array orbundle of very tiny, short tubes, each of which, under properconditions, can emit a large number of electrons from one endwhen an X-ray photon strikes the other end. The number ofelectrons emitted depends upon the X-ray flux per unit

34、 area,and thus an electron image can be produced. These devicesmust operate in a vacuum, so that a practical imaging device ispossible only with careful packaging. Usually, this will meanthat a combination of processes is required, as described morecompletely in 8.5.8.5 Combinations of Detecting Pro

35、cessesRadioscopicSystemsA variety of practical systems can be produced byvarious combinations of the basic mechanisms described,together with other devices for transforming patterns of light,electrons, or resistance changes into an image visible to thehuman eye, or which can be analyzed for action d

36、ecision in acompletely automated system. Since the amount of light orelectrical energy produced by the detecting mechanism isnormally orders of magnitude below the range of humansenses, some form of amplification or intensification is com-mon. Figs. 1-11 illustrate the basic configuration of practic

37、alsystems in use. For details of their performance and applicationsee Section 10. Table 1 compares several common imagingsystems in terms of general performance, complexity, andrelative costs.9. Radiation Sources9.1 General:9.1.1 The sources of radiation for radioscopic imagingsystems described in t

38、his guide are X-ray machines andradioactive isotopes. The energy range available extends froma few keV to 32 MeV. Since examination systems in generalrequire high dose rates, X-ray machines are the primaryradiation source. The types of X-ray sources available areconventional X-ray generators that ex

39、tend in energy up to 750keV. Energy sources from 1 MeV and above may be the Van deGraaff generator, linear accelerator, or the betatron. HighFIG. 1 Basic FluoroscopeE1000 164energy sources with large flux outputs make possible thereal-time examination of greater thicknesses of material.9.1.2 Usable

40、isotope sources have energy levels from84 keV (Thulium-170, Tm170) up to 1.25 MeV (Cobalt-60,Co60). With high specific activities, these sources should beconsidered for special application where their field mobilityand operational simplicity can be of significant advantage.9.1.3 The factors to be co

41、nsidered in determining thedesired radiation source are energy, focal geometry, duty cycle,wave form, half life, and radiation output.9.2 Selection of Sources:9.2.1 Low EnergyThe radiation source selected for aspecific examination system depends upon the material beingexamined, its mass, its thickne

42、ss, and the required rate ofexamination. In the energy range up to 750 keV, the X-ray unitshave an adjustable energy range so that they are applicable toa wide range of materials. Specifically, 50-keV units operatedown to a few keV, 160-keV equipment operates down to20 keV, and 450-keV equipment ope

43、rates down to about 25keV. A guide to the use of radiation sources for some materialsis given in Table 2.9.2.2 High-Energy SourcesThe increased efficiency ofX-ray production at higher accelerating potentials makesavailable a large radiation flux, and this makes possible theexamination of greater thi

44、cknesses of material. High-radiationenergies in general produce lower image contrast, so that as aguide the minimum thickness of material examined should notbe less than three-half value layers of material. The maximumthickness of material can extend up to ten-half value layers.Table 3 is a guide to

45、 the selection of high-energy sources.FIG. 2 Fluoroscope with OpticsFIG. 3 Light-Intensified FluoroscopeFIG. 4 Light-Intensified Fluoroscope with OpticsFIG. 5 LLLTV FluoroscopeE1000 1659.3 Source Geometry:9.3.1 While an X-ray tube with a focal spot of 3 mm(0.12 in.) operating at a target to detector

46、 distance of 380 mm(15 in.) and penetrating a 25-mm (1-in.) thick material wouldcontribute an unsharpness of 0.2 mm (0.008 in.), a detectorunsharpness of 0.5 to 0.75 mm would still be the principalsource of unsharpness.9.3.2 The small source geometry of microfocus X-ray tubespermits small target-to-

47、detector spacings and object projectionmagnification for the detection of small anomalies. The selec-tion of detectors with low unsharpness is of particular advan-tage in these cases to the reduce the focal spot-detector distance(FDD). With high magnification, the focal spot size would bethe princip

48、al source of unsharpness.FIG. 6 Light-Intensified LLLTV FluoroscopeFIG. 7 Scintillator Arrays, TV ReadoutFIG. 8 X-ray Image IntensifierE1000 1669.3.3 Where isotopes are to be evaluated for radioscopicsystems, the highest specific activities that are economicallypractical should be available so that

49、source size is minimized.9.4 Radiation Source Rating Requirements:9.4.1 The X-ray equipment selected for examination shouldbe evaluated at its continuous duty ratings, because theeconomy of radioscopic examination is realized in continuousproduction examination. X-ray units with target cooling byfluids are usually required.9.4.2 High-energy sources, for example linear accelerators,which can operate at pulse rates up to 400 pulses per second,may produce interference lines. These lines can be minimizedby the design of the real-time systems. Other lower energyX-ray gene