1、Designation: E2903 13E2903 18Standard Test Method forMeasurement of the Effective Focal Spot Size of Mini andMicro Focus X-ray Tubes1This standard is issued under the fixed designation E2903; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, the year of 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 The image quality and the resolution of X-ray images highly depend on the characteristics
3、of the focal spot. The imagingqualities of the focal spot are based on its two dimensional intensity distribution as seen from the imaging place.1.2 This test method provides instructions for determining the effecting size (dimensions) of mini and micro focal spots ofindustrial X-ray tubes. It is ba
4、sed on the European standard, EN 125435, Non-destructive testing - Characteristics of focal spotsin industrial X-ray systems for use in non-destructive testing - Part 5: Measurement of the effective focal spot size of mini andmicro focus X-ray tubes.1.3 This standard specifies a method for the measu
5、rement of effective focal spot dimensions from 5 up to 300 m of X-raysystems up to and including 225 kV tube voltage, by means of radiographs of edges. Larger focal spots should be measured usingTest Method E1165 Standard Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhol
6、e Imaging.1.4 The same procedure can be used at higher kilovoltages by agreement, but the accuracy of the measurement may be poorer.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.6 This standard does not purport to addr
7、ess all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.7 This international standar
8、d was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referen
9、ced Documents2.1 ASTM Standards:2E1165 Test Method for Measurement of Focal Spots of Industrial X-Ray Tubes by Pinhole ImagingE1255 Practice for RadioscopyE1742E1742/E1742M Practice for Radiographic ExaminationE1815 Test Method for Classification of Film Systems for Industrial RadiographyE2002 Pract
10、ice for Determining Total Image Unsharpness and Basic Spatial Resolution in Radiography and RadioscopyE2033 Practice for Radiographic Examination Using Computed Radiography (Photostimulable Luminescence Method)E2446 Practice for Manufacturing Characterization of Computed Radiography SystemsE2597E259
11、7/E2597M Practice for Manufacturing Characterization of Digital Detector ArraysE2698 Practice for Radiological Examination Using Digital Detector Arrays2.2 European Standards:3EN 125435 Non-destructive testingCharacteristics of focal spots in industrial X-ray systems for use in non-destructivetestin
12、g - Part 5: Measurement of the effective focal spot size of mini and micro focus X-ray tubes1 This test method is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.01 on Radiology(X and Gamma) Method.Current edition approved J
13、une 1, 2013Feb. 1, 2018. Published June 2013February 2018. Originally approved in 2013. Last previous edition approved in 2013 asE2903 13. DOI: 10.1520/E290313.10.1520/E2903-18.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. Fo
14、r Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http:/www.ansi.org.This document is not an ASTM standard and is intended o
15、nly to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current ver
16、sionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 Definitions of Terms
17、 Specific to This Standard:3.1.1 actual focal spotthe X-ray producing area of the target as viewed from a position perpendicular to the target surface.3.1.2 effective focal spotthe X-ray producing area of the target as viewed from the image plane.4. Summary of Test Method4.1 This method is based on
18、indirect measurement of the focal spot size by measuring the geometric unsharpness then usinga geometric calculation to determine the effective focal spot dimensions (see Section 8). For this purpose, edges are imaged eitheron a film or by means of a radioscopic or digital radiographic device using
19、a relatively high geometric magnification. For a fulldescription see reference below.45. Significance and Use5.1 One of the factors affecting the image quality of a radiographic image is geometric unsharpness. The degree of geometricunsharpness is dependent upon the focal spot size of the radiation
20、source, the distance between the source and the object to beradiographed, the distance between the object to be radiographed and the image plane (film, imaging plate, Digital DetectorArray(DDA), or radioscopic detector). This test method allows the user to determine the effective focal spot size (di
21、mensions) of theX-ray source. This result can then be used to establish source to object and object to image detector distances appropriate formaintaining the desired degree of geometric unsharpness or maximum magnification possible, or both, for a given radiographicimaging application. The accuracy
22、 of this method is dependent upon the spatial resolution of the imaging system, magnification,and signal-to-noise of the resultant images.6. Apparatus6.1 The following equipment is required for the measurement if using X-ray film:6.1.1 A test object as described in 6.5.6.1.2 X-ray films, without scr
23、eens, of sufficient size to image magnified test object and region around test object to obtain aprofile as shown in Fig. 1.6.1.3 Film cassettes made of low absorbing material (for example polyethylene).6.1.4 A film holder.4 Fry, Ewert, Gollwitzer, Neuser, and Selling, “Measuring microfocal spots us
24、ing digital radiography” Materials Evaluation,Evaluation, Vol 70, No. 8, August 2012, p.981.FIG. 1 Profile of Test Object Image (Test Object: Pt wire 1 mm)E2903 1826.1.5 A film processing unit.6.1.6 A film scanner capable of reading densities greater than 3.0 configured such that the pixel size is a
25、ppropriate for themeasurement (refer to Section 7).The film shall be of sufficient size to image the magnified test object and region around test objectto obtain a profile as shown in Fig. 1.6.1.7 The film system shall meet the requirements of Test Method E1815 film system class I, II, or Special.6.
26、2 The following equipment is required for the measurement if using computed radiography (CR):6.2.1 A test object as described in 6.5.6.2.2 A computed radiography system, consisting of an imaging plate and scanner, configured such that the pixel size isappropriate for the measurement (refer to Sectio
27、n 7). The imaging plate shall be of sufficient size to image test object and regionaround test object to obtain a profile as shown in Fig. 1.6.2.3 The computed radiography system shall meet the requirements of Practice E2446 class I, II, or Special, and image platesshall be packed in low absorption
28、cassettes using no screens.6.3 The following equipment is required for the measurement if using a radioscopic or digital detector array device:6.3.1 A test object as described in 6.5.6.3.2 A radioscopic device, for example any image intensifier with video equipment or Digital Detector Array, configu
29、red suchthat the pixel size is appropriate for the measurement (refer to Section 7), or6.3.3 A Digital Detector Array system meeting the requirements of Practice E2597E2597/E2597M. The digital Detector Arraycover should be constructed of low X-ray absorption material and should be free of cluster ke
30、rnel pixels as defined in PracticeE2597E2597/E2597M.6.3.4 The imaging area shall be of sufficient size to image magnified test object and region around test object to obtain a profileas shown in Fig. 1.6.4 Image processing equipment as follows:6.4.1 An image processing device with the capability of
31、producing linearized intensity profiles (signal is linear with dose),integration of profiles, and profile plots within the digital image in two directions perpendicular to each other, and with thecapability to measure distances.6.5 The test object shall be either a set of wires or a sphere consistin
32、g of highly absorbing material (for example tungsten,tungsten alloy, or platinum). The diameter of the wire or sphere should be greater than 20 times the focal spot dimension if thefocal spot is less than 40 m to minimize edge penetration; otherwise, the diameter should be 0.8 to 1.0 mm for focal sp
33、ots greaterthan 40 m. The diameter shall be known to within 61 %.6.5.1 In case of using two single crossed wires they shall cross each other at an angle of 90 6 3. The wires shall be mountedacross a circular aperture in a stable frame, in such a manner that the crossing point is located in the cente
34、r of the aperture. In caseof using the sphere it shall be mounted on a thin polyethylene support or placed into a thin polyethylene envelope.6.5.2 The Unsharpness Gauge of Practice E2002 is recommended as a test object of defined accuracy. Two exposures shall betaken with the wire set in perpendicul
35、ar directions to obtain the length and width of the focal spot.6.5.3 The mounting frame shall be of a size that enables the test object to be positioned very close to or on the window of theX-ray tube.7. Procedure7.1 Any use of additional X-ray pre-filtering should be avoided.7.2 The X-ray voltage (
36、in kV) should not exceed ten times the focal spot size in m for precise measurements of focal spotsbelow 20 m.7.3 Image capture requirements:7.3.1 The distance between test object and detector shall enable projective magnification (see Fig. 2), where smaller focal spotsrequire larger magnification.7
37、.3.2 Precision is dependent upon the spatial resolution of the imaging system, magnification, and signal-to-noise of theresultant images (See Footnote 4). If an estimate of the focal spot size, s, is available, then an optimal magnification can becomputed:Moptimal5111.1SNRP/ soptimal! (1)Moptimal511
38、1.1SNRP/ sestimated! (1)where:SNR = unattenuated Signal-to-Noise ratio outside the objectP = pixel size7.3.2.1 If the actual magnification is less than or equal to Moptimal, then the estimated precision is:Precisionestimated50.71=1nu1!#2 11nu2!#23100% (2)E2903 183where:n(u1) = number of pixels acros
39、s the 50 to 84 % profile on one side (E to F in Fig. 1)n(u2) = number of pixels across the 50 to 84 % profile on the other side (G to H in Fig. 1)7.3.2.2 If the actual magnification is greater than Moptimal, then the estimated precision is:Precisionestimated52SNR3100% (3)7.3.2.3 In many cases the op
40、timal magnification cannot be achieved due to the distance required. However, adequate precisionmay still be obtained by using lesser magnification. In general, the diameter of the test object image should be as large as possiblewithin the active area of the imaging medium while leaving room to make
41、 profile measurements.7.3.3 The minimum distance between the test object and the focal spot (distance “a” in Fig. 2) shall be at least five times thewire or sphere diameter.7.3.4 In case of using a cross wire or Practice E2002 Unsharpness Gauge, its plane shall be parallel within 63 to the detectorp
42、lane and X-ray tube output window.7.3.5 In case of using a film, the exposure time shall result in a background density outside the test object of the radiograph filmof D = 2.5 6 0.5. If no shutter is used, the exposure time shall exceed 30 seconds.7.3.6 In the case of using computed radiography, a
43、digital detector array, or a radioscopic device, the mean pixel value in thebackground image outside the test object should be 75 % of saturation for the system settings selected. When using a DDA orradioscopic device, if the mean pixel value is less than 75 % of saturation, then frames may be added
44、 together to achieve 75 %.7.3.7 Capture an image. Perform film radiography in accordance with Practice E1742E1742/E1742M. Operate computedradiography systems in accordance with Practice E2033. Operate DDA systems in accordance with Practice E2698. Operateradioscopy systems in accordance with Practic
45、e E1255. No image quality indicators are used.7.3.8 If X-ray film is used, scan the film with a scanner as specified in 6.1.6 in accordance with the film scanner manufacturerinstructions.8. Calculation of Results8.1 Line scans shall be produced of the image in length and width direction, see Fig. 1.
46、8.1.1 The measurement shall be made using an image processor in accordance with 6.5.1. Line averaging may be used to reducenoise if using wires or the Practice E2002 gauge ensuring that the wire aligns with the pixel matrix such that the wire edge imageremains within one pixel width along the averag
47、ed section of the wire.8.2 From these scans the imaging plane diameters DW and DL of the test object in width and length direction shall be measuredat 50 % of the total image contrast (diameter is the distance between points F and G.) The length and width directions should berelated back by geometry
48、 to the X-ray tube housing.8.3 The geometrical magnification is shown in the following Eq 4ML,W5DL,WDreal (4)where:Dreal = the real diameter8.4 In case of the crossed wires both wires have to be measured because of their different magnifications.8.5 Referring to Fig. 2 and using simple geometry, the
49、 following equations are establisheds/a5U/b (5)s5Ua/b5U/M 2 1! (6)FIG. 2 Positioning of Test ObjectE2903 184U is the sum of the spatial distance between S50 and S84 on each side of ball or wire to average the focal spot effect on U. Theoutside half of the line profile is used to avoid additional unsharpness due to edge transmission.U5EF 1GH (7)8.6 Then, according to Fig. 1, the points A and D are obtained at 84 % of the contrast. From the projection the effective focalspot dimensions sL and sW are calculated using Eq 8 and Eq 9:sL 51.473EF 1GH
