ASTM B567-98

Designation: B 567 – 98
Standard Test Method for
Measurement of Coating Thickness by the Beta Backscatter
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Method
This standard is issued under the fixed designation B 567; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript 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. Scope is called “activity.” Therefore, in beta backscatter measure-
ments, a higher activity corresponds to a greater emission of
1.1 This test method covers the beta backscatter gages for
beta particles. The activity of a radioactive element used in beta
the nondestructive measurement of metallic and nonmetallic
backscatter gages is generally expressed in microcuries (1
coatings on both metallic and nonmetallic substrate materials.
4
μCi 5 3.7 3 10 disintegrations per second).
1.2 The test method measures the mass of coating per unit
3.1.2 aperture—the opening of the mask abutting the test
area, which can also be expressed in linear thickness units
specimen. It determines the size of the area on which the
provided that the density of the coating is known.
coating thickness is measured. This mask is also referred to as
1.3 The test method is applicable only if the atomic numbers
a platen, an aperture plate, a specimen support, or a specimen
or equivalent atomic numbers of the coating and substrate
mask.
differ by an appropriate amount (see 7.2).
3.1.3 backscatter—when beta particles pass through matter,
1.4 Beta backscatter instruments employ a number of dif-
they collide with atoms. Among other things, this interaction
ferent radioactive isotopes. Although the activities of these
will change their direction and reduce their speed. If the
isotopes are normally very low, they can present a hazard if
deflections are such that the beta particle leaves the body of
handled incorrectly. This standard does not purport to address
matter from the same surface at which it entered, the beta
the safety issues and the proper handling of radioactive
particle is said to be backscattered.
materials. It is the responsibility of the user to comply with
3.1.4 backscatter coeffıcient—the backscatter coefficient of
applicable State and Federal regulations concerning the han-
a body, R, is the ratio of the number of beta particles
dling and use of radioactive material. Some States require
backscattered to that entering the body. R is independent of the
licensing and registration of the radioactive isotopes.
activity of the isotope and of the measuring time.
1.5 This standard does not purport to address all of the
3.1.5 backscatter count:
safety concerns, if any, associated with its use. It is the
3.1.5.1 absolute backscatter count—the absolute backscat-
responsibility of the user of this standard to establish appro-
ter count, X, is the number of beta particles that are backscat-
priate safety and health practices and determine the applica-
tered during a finite interval of time and displayed by the
bility of regulatory limitations prior to use.
instrument. X will, therefore, depend on the activity of the
2. Referenced Documents
source, the measuring time, the geometric configuration of the
measuring system, and the properties of the detector, as well as
2.1 International standard:
the coating thickness and the atomic numbers of the coating
ISO 3543: Metallic and Nonmetallic Coatings—
and substrate materials. X is the count produced by the
Measurement of Thickness—Beta Backscatter Method 0
uncoated substrate, and Xs, that of the coating material. To
3. Terminology
obtain these values, it is necessary that both these materials are
available with a thickness greater than the saturation thickness
3.1 Descriptions of Terms:
(see 3.1.12).
3.1.1 activity—the nuclei of all radioisotopes are unstable
3.1.5.2 normalized backscatter—the normalized backscat-
and tend to change into a stable condition by spontaneously
ter, x , is a quantity that is independent of the activity of the
emitting energy or particles, or both. This process is known as n
source, the measuring time, and the properties of the detector.
radioactive decay. The total number of disintegrations during a
The normalized backscatter is defined by the equation:
suitably small interval of time divided by that interval of time
X 2 X
0
x 5
n
X 2 X
1 s 0
This test method is under the jurisdiction of ASTM Committee B-8 on Metallic
and Inorganic Coatingsand is the direct responsibility of Subcommittee B08.10 on
where:
General Test Methods.
X 5 count from the substrate,
Current edition approved Nov. 10, 1998. Published January 1999. Originally 0
published as B 567 – 72. Last previous edition B 567 – 91 (1997).
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
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