ASTM E803-17 Standard Test Method for Determining the LD Ratio of Neutron Radiography Beams.pdf

1、Designation: E803 17Standard Test Method forDetermining the L/D Ratio of Neutron Radiography Beams1This standard is issued under the fixed designation E803; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision.

2、 A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This test method defines an empirical technique for themeasurement of the effective collimation ratio, L/D, of neutronradiography b

3、eams. The technique is based upon analysis of aneutron radiographic image and is independent of measure-ments and calculations based on physical dimensions of thecollimation system. The values derived by this techniqueshould be more accurate than those based on physicalmeasurements, particularly for

4、 poorly defined apertures.1.2 This test method covers both the manufacture and use ofthe device to measure L/D ratios.1.3 Neutron images for this method can be produced onradiographic film using an appropriate conversion screen asdetailed in Guide E748 or a CR screen with appropriateneutron converte

5、r. The method has not been validated withimages produced by digital detector arrays.1.4 This test method only applies to neutron beam lines withcold or thermal neutron spectrums.1.5 The values stated in SI units are to be regarded asstandard.1.6 This standard does not purport to address all of thesa

6、fety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.7 This international standard was developed in accor-da

7、nce with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM St

8、andards:2E748 Guide for Thermal Neutron Radiography of MaterialsE1316 Terminology for Nondestructive Examinations3. Summary of Test Method3.1 Determination of neutron beam L/D ratio (length of thebeam line divided by the diameter of the aperture) using theNU (no umbra) technique3is accomplished by r

9、adiographingthe NU device with the neutron beam to be measured andsubsequently analyzing the resulting image by one of threemethods. Each of the three methods is based upon thedetermination of that point at which the umbral shadow widthreaches zero. See Fig. 1. The neutron radiography method isdiscu

10、ssed in Guide E748 and the terms are defined in Termi-nology E1316.4. Significance and Use4.1 The quality of a neutron radiographic image is depen-dent upon many factors. The L/D ratio is one of those factorsand constitutes a numerical definition of the geometry of theneutron beam. The L/D ratio req

11、uired for a specific neutronradiographic examination is dependent upon the thickness ofthe specimen and the physical characteristics of the particularelement of interest. Use of this test method allows theradiographer and the user to determine and periodically mea-sure the effective collimation rati

12、o.5. Apparatus5.1 The NU Device (see Fig. 2(a) and (b), and Fig. 3)employs neutron absorbing rods positioned at various distancesfrom the image plane. In practice this device consists ofcadmium rods located in V-grooves accurately machined in the1This test method is under the jurisdiction of Committ

13、ee E07 on NondestructiveTesting and is the direct responsibility of Subcommittee E07.05 on Radiology(Neutron) Method.Current edition approved Nov. 1, 2017. Published November 2017. Originallyapproved in 1986. Last previous edition approved in 2013 as E803 91(2013). DOI:10.1520/E0803-17.2For referenc

14、ed ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Newacheck, R. L., and Underhill, P. E., “The NU Method for Determining L/

15、DRatio Of Neutron Radiography Facilities,” Aerotest Operations, Inc., Report A.O.77-27, June 1977.*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 StatesThis international stand

16、ard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1surfac

17、e of an aluminum channel section set at a 45 614 angleto the side support plate. Near the image plane end theV-grooves are machined on 0.283-cm centers. After 21V-grooves, counting one on the end, the grooves are machinedon 0.707-cm centers to the source end. The 0.64-mm diametercadmium rods are lai

18、d into the V-grooves and secured withneutron transparent adhesive tape. The aluminum channel issupported by side plates to maintain the 45 614 anglerelative to the image plane. Nylon rods included in the groovesadjacent to the cadmium rods are present in some devices.These nylon rods are not used in

19、 L/D calculations, nor do theydetract from the function of the device, and so are consideredoptional.5.2 A single A unit or B unit as shown in Fig. 2(b) and Fig.3 can be used for L/D values expected to be less than 150,while multiple device segments can be used in combination tomeasure larger L/D ra

20、tios.Alternately, a singleAor B unit usedwith appropriate spacers may be used to accommodate a widerange of L/D values when using the methods described in 7.1or 7.3 to establish the collimation ratio.6. Procedure6.1 Align the plane of the imaging device perpendicular tothe axis of the neutron beam.6

21、.2 Insert spacers of known thickness, if required.6.3 Place the NU device against the imaging device (orspacers) with the finely spaced rods nearest the imaging deviceif using an A unit.6.4 Film Procedure:6.4.1 Expose the single-emulsion film and NU device for atime span that will produce a nominal

22、background film densityof 2.5 6 0.4.6.4.2 Process the exposed film in accordance with themanufacturers recommendations.6.4.3 Analyze the resultant image in accordance with one ormore of the three methods outlined in Section 7.6.4.4 Digitization of film (optional) should be performedwith a transmissi

23、on scanner. A minimum of 300 dpi forscanning is required. Accuracy is improved considerably at orabove 600 dpi.FIG. 1 Diagram of Zero Umbra Image ConfigurationNOTE 1Rods at “A” positions are 1 cm each side of center line (22 ea.)NOTE 2Rods at “B” positions are 2 cm each side of center line (9 ea.)NO

24、TE 3Rods at “C” positions are 2.5 cm each side of center line (1 ea.)NOTE 4All dimensions from base line to reduce accumulative errorsNOTE 5Rod arrangement shown for single system device. For an add-on device, to form a double system, extend the 11 spaces for 7.78 cm to 19spaces for 13.43 cm and eli

25、minate the close spacing (20 for 5.65 cm)NOTE 6Rods held tightly in position with one layer of transparent tapeFIG. 2 (a) Support Channel Subassembly with Rod SpacingE803 1726.5 CR Procedure:6.5.1 CR images must be produced using an image platewith either an embedded conversion material (i.e. gadoli

26、nium),or a high resolution image plate pressed against a suitableconversion screen. High resolution and low noise are bothrequired for accurate determination of the L/D ratio.6.5.2 Expose the CR screen for a sufficient duration tooptimize image production.6.5.3 Scan the imaging phosphor with 100 um

27、or smallerpixel pitch.6.5.4 Produce the image without any edge enhancement, orother image enhancements.6.5.5 Analyze the resulting image in accordance with thevisual or line plot analysis method.7. Data AnalysisThe alternative line plot analysis method described insection 7.3 has the best repeatabil

28、ity, but is not suitable for usewith current CR systems. A CR system with 15 um or smallerpixel pitch might be able to use the method detailed in 7.3.When generating line plots, averaging through the use of amultiple pixel wide line substantially improves repeatability ofthe results.7.1 Visual Analy

29、sisAvisual determination of the L/D ratiocan be made directly from the neutron radiographic image.When observing the individual rod images, the umbral imagecan be recognized as the “white” line along the center of therod image. This “white” line will decrease in width for the rodslocated farther and

30、 farther from the film. At some point theumbral images will disappear. Beyond this point a less intensewhite line will appear and increase in width with increasing roddistance. Use ofa5to10-power magnifier for film, or digitalmagnification for digital images will aid in determining thepoint at which

31、 the “white” line disappears and then increases inwidth with a decreased intensity. Based on the visualobservation, determine the rod with zero umbral width andthen determine its distance (b) from the cassette. The L/D ratiois calculated as follows:FIG. 2 (b) L D Apparatus Assembly (continued)E803 1

32、73L/D 5 b/rod diameter!7.2 Line Plot AnalysisThe second data analysis method isbased on a microdensitometric, line plot from a digitized film,or a line plot from a digital CR image. The line plot is takenacross the cadmium rod images beginning with the “0” positionrod nearest the film. A typical lin

33、e plot is shown in Fig. 4. Thevalue of b is obtained from the intersection of a straight lineoriginating from the tip (low film density) of the scan of the “0”rod and a curved line through the tips of the remaining waveforms as shown in Fig. 4. This method is suitable for use forL/D ratios up to a f

34、ew hundred. Higher L/D ratios cannot bedetermined accurately by this method due to the inability toobtain a stable wave form for large values of b. If spacers or anoffset distance are present between the E803 device and theimaging device, this method cannot be used.7.3 Alternative Line Plot Analysis

35、This method uses a lineplot or scanning microdensitometric traces for L/D ratiodeterminations and is applicable for both high and low L/Dratios. Line plots similar to those in Fig. 5 are produced, foreach wire to be analyzed.7.3.1 The umbral width is measured along a horizontal line(parallel to back

36、ground) through the average of the low-densityscan of the individual wave form (i.e. the segment correspond-ing with the umbral shadow). The desired dimension is thedistance between the intersections of this horizontal line withlines drawn through the two sides of the wave form. The unitof measureme

37、nt and scan/magnification settings must be con-sistent through measurement of all individual wave forms.7.3.2 At least two wave forms must be plotted, one near thefilm plane and one near the point where the umbra disappears.Increasing the number of wave forms plotted improves accu-racy. Care must be

38、 taken not to go beyond the point where theumbral image disappears. If the L/D devices are placed directlyagainst the imaging device, the five cadmium wires closest tothe imaging device should not be used because the unsharpnessdue to the imaging device/conversion screen combinationoverrides the uns

39、harpness due to the L/D ratio.7.3.3 These measurements and their respective distancesfrom the image plane are analyzed by a linear regressiontechnique (or alternatively by a linear best-fit curve of theplotted data) to determine the x-axis intercept. This is the valueof b. The L/D ratio is simply b/

40、rod diameter.8. Report8.1 The specific image capture method utilized shall bereported, including digitization method if film images aredigitized.8.2 The calculation method(s) used to determine the L/Dratio shall be reported.FIG. 3 NU Device PictorialsE803 1749. Precision and Bias9.1 The repeatabilit

41、y standard deviation from a single op-erator has been determined for each of the three data analysismethods detailed in the standard. For the Visual Analysismethod, standard deviation was determined to be 3.91 (2.7%)and the 95 % repeatability limit was 10.9 (7.4%). For the LinePlot Analysis method,

42、standard deviation was determined to be4.78 (3.1%) and the 95 % repeatability limit was 13.4 (8.8%).For the Alternative Line Plot Analysis method, standarddeviation was determined to be 2.44 (1.6%) and the 95 %repeatability limit was 6.8 (4.5%). These values are represen-tative of the repeatability

43、that can be achieved; consistency ofsetup (angle and offset distance), the L/D at the facility,consistency of cadmium wire diameter and the resolution of theimaging device, as well as other factors, may affect therepeatability.9.2 It is not possible to specify the precision of the proce-dure in Test

44、 Method E803 for measuring the reproducibility asFIG. 4 Microdensitometer Scan 1:1FIG. 5 Film Density Scans of Individual Cadmium Rods 50:1E803 175targeted results for the imaging systems L/D do not exist. Thistest represents a more accurate method to measure the colli-mation ratio of a particular i

45、maging system than reliance on asbuilt values. The accuracy of this method will be determined bythe tolerances on the device construction, imaging setup, andimage noise, as well as other factors.NOTE 1Data for repeatability determination was collected from 25neutron radiographs imaged at the same be

46、am line on the same day. Theseimages were digitized using a transmission scanner for the Line PlotAnalysis and Alternative Line Plot Analysis methods, while the originalfilms were used for the Visual Analysis method. The mean L/D ratioscalculated by each method were 146.7 63.9 (VisualAnalysis), 153.

47、0 64.8(Line Plot Analysis), and 149.9 62.4 (Alternative Line Plot Analysis).9.3 BiasNo information can be presented on the bias ofthe procedure in Test Method E803 for measuring the L/DRatio of Neutron Imaging Beams as targeted results for thesystem to not exist.10. Keywords10.1 beam collimation; L/

48、D ratio; neutron imaging; neutronradiography; radiographic unsharpness; umbral shadowAPPENDIXES(Nonmandatory Information)X1. THEORYX1.1 The collimation ratio of a neutron radiography beam isdefined as the distance between the source and the image plane(L) divided by the diameter of the source (D). S

49、ince the sourcediameter (D) is typically large (2 cm), and because materialswith very high neutron attenuation coefficients are available, aunique approach to L/D ratio determination is possible. If anopaque rod with a diameter much smaller than the sourcediameter is placed near the image plane, an umbral shadow willbe cast as shown in Fig. X1.1.X1.2 For a given source diameter (D) and a given roddiameter (d), there will be a rod to image plane distance (b)where the width of the umbral shadow on the image plane willequal zero. For