ASTM B567-98 (R2021) pdf free download.Standard Test Method for Measurement of Coating Thickness by the Beta Backscatter Method.
1.1 This test method covers the beta hackscatter gages for the nondestructive measurement of metallic and nonmetallic coatings on both metallic and nonmetallic substrate materials.
1.2 The test method measures the mass of coating per unit area, which can also be expressed in linear thickness units provided that the density of the coating is known.
1.3 The test method is applicable only if the atomic numbers or equivalent atomic numbers of the coating and substrate differ by an appropriate amount (see 6.2).
1.4 Beta backscatter instruments employ a number of different radioactive isotopes. Although the activities of these isotopes are normally very low, they can present a hazard if handled incorrectly. This standard does not purport to address the safety issues and the proper handling of radioactive materials. It is the responsibility of the user to comply with applicable State and Federal regulations concerning the handling and use of radioactive material. Some States require licensing and registration of the radioactive isotopes.
1.5 The values stated in SI units are to he regarded as standard. No other units of measurement are included in this standard.
2.1.2 aperture—the opening of the mask abutting the test specimen. It determines the size of the area on which the coating thickness is measured. This mask is also referred to as a platen, an aperture plate, a specimen support, or a specimen mask.
2.1.3 hackscatter—when beta particles pass through matter. they collide with atoms. Among other things, this interaction will change their direction and reduce their speed. If the deflections are such that the beta particle leaves the body of matter from the same surface at which it entered, the beta particle is said to be backscattered.
2.1.4 hackscatter coefficient—the backscatter coellicient of a body, R, is the ratio of the number of beta particles backscattered to that entering the body. R is independent of the activity of the isotope and of the measuring time.
2. 1 .5 hackscatter count:
2. 1 .5. 1 absolute hackscaner count—the absolute hackscat— ter count. X, is the number of beta particles that are hackscattered during a unite interval of time and displayed by the instrument. X will, therefore, depend on the activity of the source, the measuring time, the geometric configuration of the measuring system. and the properties of the detector, as well as the coating thickness and the atomic numbers of the coating and substrate materials. X0 is the count produced by the uncoated substrate, and Xs, that of the coating material. To obtain these values, it is necessary that both these materials are available with a thickness greater than the saturation thickness (see 2.1.12).ASTM B567 pdf download.