ASTM B567-1998(2003) Standard Test Method for Measurement of Coating Thickness by the Beta Backscatter Method《用β射线反向散射法测定覆层厚度的标准试验方法》.pdf
《ASTM B567-1998(2003) Standard Test Method for Measurement of Coating Thickness by the Beta Backscatter Method《用β射线反向散射法测定覆层厚度的标准试验方法》.pdf》由会员分享,可在线阅读,更多相关《ASTM B567-1998(2003) Standard Test Method for Measurement of Coating Thickness by the Beta Backscatter Method《用β射线反向散射法测定覆层厚度的标准试验方法》.pdf(9页珍藏版)》请在麦多课文档分享上搜索。
1、Designation: B 567 98 (Reapproved 2003)Standard Test Method forMeasurement of Coating Thickness by the Beta BackscatterMethod1This standard is issued under the fixed designation B 567; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision
2、, 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.This standard has been approved for use by agencies of the Department of Defense.1. Scope1.1 This test method cover
3、s the beta backscatter gages forthe nondestructive measurement of metallic and nonmetalliccoatings on both metallic and nonmetallic substrate materials.1.2 The test method measures the mass of coating per unitarea, which can also be expressed in linear thickness unitsprovided that the density of the
4、 coating is known.1.3 The test method is applicable only if the atomic numbersor equivalent atomic numbers of the coating and substratediffer by an appropriate amount (see 7.2).1.4 Beta backscatter instruments employ a number of dif-ferent radioactive isotopes. Although the activities of theseisotop
5、es are normally very low, they can present a hazard ifhandled incorrectly. This standard does not purport to addressthe safety issues and the proper handling of radioactivematerials. It is the responsibility of the user to comply withapplicable State and Federal regulations concerning the han-dling
6、and use of radioactive material. Some States requirelicensing and registration of the radioactive isotopes.1.5 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 a
7、nd health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 International standard:ISO 3543: Metallic and Nonmetallic CoatingsMeasurement of ThicknessBeta Backscatter Method3. Terminology3.1 Descriptions of Terms:3.1.1 activitythe nuclei of
8、all radioisotopes are unstableand tend to change into a stable condition by spontaneouslyemitting energy or particles, or both. This process is known asradioactive decay. The total number of disintegrations during asuitably small interval of time divided by that interval of timeis called “activity.”
9、 Therefore, in beta backscatter measure-ments, a higher activity corresponds to a greater emission ofbeta particles. The activity of a radioactive element used in betabackscatter gages is generally expressed in microcuries (1Ci = 3.7 3 104disintegrations per second).3.1.2 aperturethe opening of the
10、mask abutting the testspecimen. It determines the size of the area on which thecoating thickness is measured. This mask is also referred to asa platen, an aperture plate, a specimen support, or a specimenmask.3.1.3 backscatterwhen beta particles pass through matter,they collide with atoms. Among oth
11、er things, this interactionwill change their direction and reduce their speed. If thedeflections are such that the beta particle leaves the body ofmatter from the same surface at which it entered, the betaparticle is said to be backscattered.3.1.4 backscatter coeffcientthe backscatter coefficient of
12、a body, R, is the ratio of the number of beta particlesbackscattered to that entering the body. R is independent of theactivity of the isotope and of the measuring time.3.1.5 backscatter count:3.1.5.1 absolute backscatter countthe absolute backscat-ter count, X, is the number of beta particles that
13、are backscat-tered during a finite interval of time and displayed by theinstrument. X will, therefore, depend on the activity of thesource, the measuring time, the geometric configuration of themeasuring system, and the properties of the detector, as well asthe coating thickness and the atomic numbe
14、rs of the coatingand substrate materials. X0is the count produced by theuncoated substrate, and Xs, that of the coating material. Toobtain these values, it is necessary that both these materials areavailable with a thickness greater than the saturation thickness(see 3.1.12).3.1.5.2 normalized backsc
15、atterthe normalized backscat-ter, xn, is a quantity that is independent of the activity of thesource, the measuring time, and the properties of the detector.The normalized backscatter is defined by the equation:xn5X 2 X0Xs2 X01This test method is under the jurisdiction of ASTM Committee B08 on Metal
16、licand Inorganic Coatings and is the direct responsibility of Subcommittee B08.10 onTest Methods.Current edition approved Oct. 1, 2003. Published October 2003. Originallyapproved in 1972. Last previous edition approved in 1998 as B 567 98.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box
17、C700, West Conshohocken, PA 19428-2959, United States.where:X0= count from the substrate,Xs= count from the coating material, andX = count from the coated specimen, and each count is forthe same interval of time.Because X is always $X0and # Xs, xncan only take valuesbetween 0 and 1. (For reasons of
18、simplicity, it is oftenadvantageous to express the normalized count as a percentageby multiplying xnby 100.)3.1.5.3 normalized backscatter curvethe curve obtainedby plotting the coating thickness as a function of xn.3.1.6 beta particlesbeta particles or beta rays are high-speed electrons that are em
19、itted from the nuclei of materialsundergoing a nuclear transformation. These materials arecalled beta-emitting isotopes, beta-emitting sources, or betaemitters.3.1.7 coating thicknessin this test method, coating thick-ness refers to mass per unit area as well as geometricalthickness.3.1.8 dead time
20、or resolving timeGeiger-Mller tubesused for counting beta particles have characteristic recoverytimes that depend on their construction and the count rate.After reading a pulse, the counter is unresponsive to successivepulses until a time interval equal to or greater than its dead timehas elapsed.3.
21、1.9 energyit is possible to classify beta emitters by themaximum energy of the particles that they release during theirdisintegration. This energy is generally given in mega-electronvolts, MeV.3.1.10 equivalent (or apparent) atomic number theequivalent atomic number of an alloy or compound is theato
22、mic number of an element that has the same backscattercoefficient as the material.3.1.11 half-life, radioactivefor a single radioactive decayprocess, the time required for the activity to decrease by half.3.1.12 saturation thicknessthe minimum thickness of amaterial that produces a backscatter that
23、is not changed whenthe thickness is increased. (See also Appendix X1.)3.1.13 sealed source or isotopea radioactive sourcesealed in a container or having a bonded cover, the container orcover being strong enough to prevent contact with and disper-sion of the radioactive material under the conditions
24、of use andwear for which it was designed.3.1.14 source geometrythe spatial arrangement of thesource, the aperture, and the detector with respect to each other.4. Summary of Test Method4.1 When beta particles impinge upon a material, a certainportion of them is backscattered. This backscatter is esse
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