1、Designation: E803 91 (Reapproved 2013)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, t
2、he 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 This test method defines an empirical technique for the measurement of the effective collimation rat
3、io, L/D, of neutronradiography beams. The technique is based upon analysis of a neutron radiographic image and is independent of measurementsand calculations based on physical dimensions of the collimatorcollimation system. The values derived by this technique shouldbe more accurate than those based
4、 on physical measurements, particularly for poorly defined apertures.1.2 This test method covers both the manufacture and use of the device to measure L/D ratios.1.3 Neutron images for this method can be produced on radiographic film using an appropriate conversion screen as detailedin Guide E748 or
5、 a CR screen with appropriate neutron converter. The method has not been validated with images produced bydigital detector arrays.1.4 This test method only applies to neutron beam lines with cold or thermal neutron spectrums.1.5 The values stated in SI units are to be regarded as standard.1.6 This s
6、tandard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability ofregulatory limitations prior to use.1.7 This in
7、ternational standard 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) C
8、ommittee.2. Referenced Documents2.1 ASTM Standards: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 the beam line divided by the diameter of the aperture) using the
9、 NU(no umbra) technique3 is accomplished by radiographing the NU device with the neutron beam to be measured and subsequentlyanalyzing the radiograph resulting image by one of three methods. Each of the three methods is based upon the determination ofthat point at which the umbral shadow width reach
10、es zero. See Fig. 1. A key feature of the NU technique is that The neutron L/Dcan be determined accurately without the need for expensive instrumentation. Neutron radiography practices are discussed inPracticesradiography method is discussed in Guide E748 and the terms are defined in Terminology E13
11、16.4. Significance and Use4.1 The quality of a neutron radiographic image is dependent upon many factors. The L/D ratio is one of those factors andconstitutes a numerical definition of the geometry of the neutron beam. The L/D ratio required for a specific neutron radiographic1 This test method is u
12、nder the jurisdiction of Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.05 on Radiology (Neutron)Method.Current edition approved June 1, 2013Nov. 1, 2017. Published June 2013November 2017. Originally approved in 1986. Last previous edition approved in 20
13、082013 asE803 91 (2008).(2013). DOI: 10.1520/E0803-91R13.10.1520/E0803-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the
14、ASTM website.3 Newacheck, R. L., and Underhill, P. E., “The NU Method for Determining L/D Ratio Of Neutron Radiography Facilities,” Aerotest Operations, Inc., Report A.O. 77-27,June 1977.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication
15、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 versionof the standard as published by ASTM is to be consider
16、ed 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 States1examination is dependent upon the thickness of the specimen and the physical characteristics of
17、the particular element of interest.Use of this test method allows the radiographer and the user to determine and periodically checkmeasure the effective collimationratio.5. Apparatus5.1 The NU Device (see Fig. 2(a) and (b), and Fig. 3) employs neutron absorbing rods positioned at various distances f
18、rom theimage plane. In practice this device consists of cadmium and nylon rods located in V-grooves accurately machined in the surfaceof an aluminum channel section set at a 45 6 14 angle to the side support plate. Near the image plane end the V-grooves aremachined on 0.283-cm centers. After 21 V gr
19、ooves, V-grooves, counting one on the end, the grooves are machined on 0.707-cmcenters to the source end. The 0.64-mm diameter cadmium and nylon rods are laid into the V-grooves and secured with neutrontransparent adhesive tape. The aluminum channel is supported by side plates to maintain the 45 6 1
20、4 angle relative to the imageplane. While cadmium rods with diameters other than 0.64 mm may be used, the exact rodNylon rods included in the groovesadjacent to the cadmium rods are present in some devices. These nylon rods are not used in diameterL/D must be known and thedepth of the V grooves must
21、 be adjusted accordingly.calculations, nor do they detract from the function of the device, and so areconsidered optional.5.2 A single A unit or B unit as shown in Fig. 2Fig. 2(b) is(b) and Fig. 3 can be used for L/D values expected to be less than150. 150, while multiple device segments can be used
22、 in combination to measure larger L/D ratios. Alternately, a single A or Bunit used with appropriate spacers may be used to accommodate a wide range of L/D values.values when using the methodsdescribed in 7.1 or 7.3 to establish the collimation ratio.FIG. 1 Diagram of Zero Umbra Image ConfigurationN
23、OTE 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.)NOTE 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 show
24、n 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 eliminate 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 S
25、pacingE803 1726. Procedure6.1 Place the NU device against the cassette with the finely spaced rods nearest the cassette.6.1 Align the plane of the cassette imaging device perpendicular to the axis of the neutron beam.6.2 Insert spacers of known thickness, if required.6.3 Place the NU device against
26、the imaging device (or spacers) with the finely spaced rods nearest the imaging device if usingan A unit.6.4 Expose the single-emulsion film and NU device for a time span that will produce a nominal background film density of 2.56 0.4.Film Procedure:6.4.1 Expose the single-emulsion film and NU devic
27、e for a time span that will produce a nominal background film density of2.5 6 0.4.6.4.2 Process the exposed film in accordance with the manufacturers recommendations.6.4.3 Analyze the resultant image in accordance with one or more of the three methods outlined in Section 7.6.4.4 Digitization of film
28、 (optional) should be performed with a transmission scanner. A minimum of 300 dpi for scanning isrequired. Accuracy is improved considerably at or above 600 dpi.6.5 Process the exposed film in accordance with the manufacturers recommendations.CR Procedure:6.5.1 CR images must be produced using an im
29、age plate with either an embedded conversion material (i.e. gadolinium), or ahigh resolution image plate pressed against a suitable conversion screen. High resolution and low noise are both required foraccurate determination of the L/D ratio.FIG. 2 (b) L D Apparatus Assembly (continued)E803 1736.5.2
30、 Expose the CR screen for a sufficient duration to optimize image production.6.5.3 Scan the imaging phosphor with 100 um or smaller pixel pitch.6.5.4 Produce the image without any edge enhancement, or other image enhancements.6.5.5 Analyze the resulting image in accordance with the visual or line pl
31、ot analysis method.6.5 Analyze the resultant image in accordance with one or more of the three methods outlined in Section 7.7. Data AnalysisThe alternative line plot analysis method described in section 7.3 has the best repeatability, but is not suitable for use with currentCR systems.ACR system wi
32、th 15 um or smaller pixel pitch might be able to use the method detailed in 7.3. When generating lineplots, averaging through the use of a multiple pixel wide line substantially improves repeatability of the results.7.1 Visual AnalysisA visual determination of the L/D ratio can be made directly from
33、 the neutron radiograph. radiographicimage. When observing the individual rod images, the umbral image can be recognized as the “white” line along the center of therod image. This “white” line will decrease in width for the rods located farther and farther from the film.At some point the umbralimage
34、s will disappear. Beyond this point a less intense white line will appear and increase in width with increasing rod distance.Use of a 5 to 10-power magnifier for film, or digital magnification for digital images will aid in determining the point at whichthe “white” line disappears and then increases
35、 in width with a decreased intensity. Based on the visual observation, determine therod with zero umbral width and then determine its distance (b) from the cassette. The L/D ratio is calculated as follows:L/D 5b/rod diameter!7.2 Microdensitometric Line Plot AnalysisThe second data analysis method is
36、 based on a microdensitometric scanmicrodensitometric, line plot from a digitized film, or a line plot from a digital CR image.The line plot is taken across the cadmiumrod images beginning with the “0” position rod nearest the film.Atypical scan line plot is shown in Fig. 4.Adensitometer apertureof
37、20 300 m and no horizontal expansion is suggested for this method. The value of b is obtained from the intersection of astraight line originating from the tip (low film density) of the scan of the “0” rod and a curved line through the tips of the remainingwave forms as shown in Fig. 4. This method g
38、ives the best resultsis suitable for use for L/D ratios up to a few hundred. HigherL/D ratios cannot be determined accurately by this method due to the inability to obtain a stable wave form for large values of b.If spacers or an offset distance are present between the E803 device and the imaging de
39、vice, this method cannot be used.7.3 Alternative Microdensitometric Line Plot AnalysisThis method also uses uses a line plot or scanning microdensitometrictraces for L/D ratio determinations and is applicable for both high and low L/D ratios. For this method the recommendedmicrodensitometer settings
40、 are: 20 300-m aperture and 50 (or more) chart recording expansion. These settings will produceindividual wave forms as shown Line plots similar to those in Fig. 5. At least two wave forms must be scanned, one near the filmplane and one other near the point where the umbra disappears. Care must be t
41、aken not to go beyond the point where the umbralimage disappears. Microdensitometer settings must remain the same for all scans. For are produced, for each wire L/D ratios above100, the “0” centimetre rod image should not be used because the unsharpness due to the film/conversion screen combinationo
42、verrides the unsharpness due to the to L/D ratio. For the lower L/D ratios (under ;100), the simplified equation using X2 andU0 for the “0” rod image may be used with good results.be analyzed.7.3.1 To determine the value of The b it is necessary to measure the umbral image width for the two rods sel
43、ected. Thisdimension umbral width is measured along a horizontal line (parallel to background) through the average of the low-density scanof the individual wave form. form (i.e. the segment corresponding with the umbral shadow). The desired dimension is the distancebetween the intersections of this
44、horizontal line with lines drawn through the two sides of the wave form. The measurement maybe centimetres or inches and need not be converted to the unmagnified value.unit of measurement and scan/magnification settingsmust be consistent through measurement of all individual wave forms.7.3.2 Using t
45、his dimension, determine the value of b as follows (see Fig. 6):b 5U1X1!/U12U2!1X0where:U1 = umbral width of a rod near the image plane,U2 = umbral image width of a rod near the distance where the umbra disappears,X0 = distance from the film to the rod chosen for U1, cm, andX1 = distance between the
46、 two rods chosen for analysis, cm.Since At least two wave forms must be plotted, one near the film plane and one near the point where the umbra disappears.Increasing the number of wave forms plotted improves accuracy. Care must be taken not to go beyond the point where the umbralimage disappears. If
47、 the L/D = devicesbrod diameter, it is possible to determine are placed directly against the imaging device, thefive cadmium wires closest to the imaging device should not be used because the unsharpness due to the imaging device/conversionscreen combination overrides the unsharpness due to the L/D
48、directly as follows: ratio.L/D 5F U1X1U12U21X0G/rod diameterE803 174For low L/D ratios (2 cm), and because materials withvery high neutron attenuation coefficients are available, a unique approach to L/D ratio determination is possible. If an opaque rodwith a diameter much smaller than the source di
49、ameter is placed near the image plane, an umbral shadow will be cast as shownin Fig. X1.1.X1.2 For a given source diameter (D) and a given rod diameter (d), there will be a rod to image plane distance (b) where the widthof the umbral shadow on the image plane will equal zero. For this particular distance a simple formula can be developed todetermine L/Dratio:XYZ is similar toSTZTherefore:L/D 5b/dwhere:L = source to film distance (Note X1.1),D = source size = XY in Fig. X1.1,b = object to film distance, andd = object size = ST in Fig. X1.1.NOTE X1
