ASTM_E_1496_-_97.pdf

Designation:E 1496 97Standard Test Method forNeutron Radiographic Dimensional Measurements1This standard is issued under the fixed designation E 1496;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 last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method provides a technique for extractingquantitative dimensional information on an object from itsneutron radiograph.The technique is based on the identifica-tion of changes in film density caused by material changeswhere a corresponding discontinuity in film density exists.Thistest method is designed to be used with neutron radiographsmade with a well-collimated beam.The film densities in thevicinity of the edge must be in the linear portion of the densityversus exposure curve.The accuracy of this test method maybe affected adversely in installations with high-angular-divergence neutron beams or with large object-to-film dis-tances.1.2 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 regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:E 94 Guide for Radiographic Testing2E 748 Practices for Thermal Neutron Radiography of Ma-terials2E 803 Method for Determining the L/D Ratio of NeutronRadiography Beams2E 1316 Terminology for Nondestructive Examination22.2Other Documents:SNT-TC-1A Recommended Practice for NondestructiveTesting Personnel Qualification and Certification3ANSI/ASNT CP-189 ASNT Standard for Qualification andCertification of Nondestructive Testing Personnel3MIL-STD-410 Nondestructive Testing Personnel Qualifica-tion and Certification43.Terminology3.1 DefinitionsDefinitions of the many terms relative toradiography(for example,X,gamma,and neutron radiogra-phy)can be found in Terminology E 1316.3.2 Definitions of Terms Specific to This Standard:3.2.1 extremumthe point on the linear response portion ofthe curve of smoothed density versus location at which theslope is a maximum.3.2.2 extremum slope criterionthe criterion that specifiesthe edge of a defect or an object,located at the spatial positioncorresponding to the extremum as determined from examina-tion of a radiograph.3.2.3 linear responsea radiographic response where thefilm density across an edge within an object is contained in thelinear part of the density versus exposure curve.3.2.4 traveling-stage microdensitometera densitometerwith a small aperture(typically between 10 to 25 m by 200 to300 m)that has the capability of scanning a radiograph in acontinuous or stepped manner and generating either a digital oran analog mapping of the film density of the radiograph as afunction of position.4.Summary of Test Method4.1 All radiation used in radiography is attenuated in itspassage through an object according to its thickness andmagnitude of the material attenuation properties appropriate tothe type and energy of radiation.Additionally,significantspatial spreading occurs due to the system imperfections,nonsymmetric radiation transport,and image formation pro-cess.Significant variations in the recorded radiation near edges1This test method is under the jurisdiction of ASTM Committee E-7 onNondestructive Testing and is the direct responsibility of Subcommittee E07.05 onRadiology(Neutron)Method.Current edition approved May 10,1997.Published February 1998.Originallypublished as E 1496 92.Last previous edition E 1496 92.2Annual Book of ASTM Standards,Vol 03.03.3Available from American Society for Nondestructive Testing,1711 ArlingatePlaza,PO Box 28518,Columbus,Ohio 43228-0518.4Available from Standardization Documents Order Desk,Building 4 Section D,700 Robbins Avenue,Philadelphia,PA 19111-5904,Attn:NPODS.FIG.1 Typical Microdensitometer Film Density Traces Associatedwith Three Rectangular Material Discontinuities:(a)Edge ofObject,(b)Thickness Variation,and(c)Dissimilar MaterialBoundary1Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959,United States.and material discontinuities therefore occur and manifestthemselves by film density variations in the radiograph,asillustrated in Fig.1.4.2 A graph of detector response(film density)versuslocation across an interface is similar in form for manydifferent types of interface,provided that the detector respondslinearly to increased exposure over the entire region of interest.Typical radiographic responses are shown in Fig.2(a)and(b).4.3 Both theoretical and experimental studies in neutronradiography have established that under commonly encoun-tered high-quality linear-response radiographic conditions,theedge of an object corresponds to that point on the smoothedexperimentally obtained microdensitom