Metallic and non-metallic coatings - Measurement of thickness - Beta backscatter method (ISO 3543:2000)

Migrated from Progress Sheet (TC Comment) (2000-07-10): See mail of Gaid Le Gall (97-03-20) ++ TC 262 Res.61 by corr.(970303): updating of existing EN (TA/970415) ++ N 201: New TD (980917)

Metallische und andere anorganische Schichten - Dickenmessung - Betarückstreu-Verfahren (ISO 3543:2000)

Diese internationale Norm legt ein Verfahren zur zerstörungsfreien Messung von Schichtdicken mit Hilfe von Betarückstreu-Meßgeräten fest. Sie gilt sowohl für metallische als auch nichtmetallische Schichten auf metallischen und nichtmetallischen Grundwerkstoffen. Um dieses Verfahren anzuwenden, müssen sich die Ordnungszahlen oder die effektiven Ordnungszahlen von Schicht- und Grundwerkstoff um einen hinreichenden Betrag unterscheiden.

Revetements métalliques et non métalliques - Mesurage de l'épaisseur - Méthode par rétrodiffusion des rayons beta (ISO 3543:2000)

AVERTISSEMENT Les instruments à rétrodiffusion des rayons bêta, utilisés pour le mesurage de l'épaisseur des revêtements, utilisent un certain nombre de sources radioactives différentes. Bien que les activités de ces sources soient généralement très faibles, elles peuvent présenter un danger pour la santé si elles ne sont pas manipulées correctement. En conséquence, tous les règlements et directives de sécurité prescrits par les autorités locales ou nationales doivent être respectés. La présente Norme internationale spécifie une méthode de mesurage non destructif de l'épaisseur des revêtements, basée sur le principe de la rétrodiffusion des rayons bêta. Elle est applicable aux revêtements métalliques ou non métalliques, que les substrats soient ou non métalliques. Pour que la présente méthode soit applicable, il faut que les numéros atomiques ou les numéros atomiques équivalents du revêtement et du substrat diffèrent d'une quantité convenable.
NOTE La méthode par rétrodiffusion des rayons bêta est de moins en moins utilisée depuis la mise en oeuvre de la méthode par fluorescence X (ISO 3497). Son faible coût en fait néanmoins une méthode très utile pour de nombreuses applications. En outre, sa plage de mesures est plus large.

Kovinske in nekovinske prevleke - Merjenje debeline - Metoda z beta povratnim sipanjem (ISO 3543:2000)

General Information

Status
Published
Publication Date
28-Feb-2002
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
01-Mar-2002
Due Date
01-Mar-2002
Completion Date
01-Mar-2002

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SLOVENSKI STANDARD
SIST EN ISO 3543:2002
01-marec-2002
1DGRPHãþD
SIST EN ISO 3543:1999
Kovinske in nekovinske prevleke - Merjenje debeline - Metoda z beta povratnim
sipanjem (ISO 3543:2000)
Metallic and non-metallic coatings - Measurement of thickness - Beta backscatter
method (ISO 3543:2000)
Metallische und andere anorganische Schichten - Dickenmessung - Betarückstreu-
Verfahren (ISO 3543:2000)

Revetements métalliques et non métalliques - Mesurage de l'épaisseur - Méthode par

rétrodiffusion des rayons beta (ISO 3543:2000)
Ta slovenski standard je istoveten z: EN ISO 3543:2000
ICS:
25.220.20 Površinska obdelava Surface treatment
25.220.40 Kovinske prevleke Metallic coatings
SIST EN ISO 3543:2002 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 3543:2002
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SIST EN ISO 3543:2002
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SIST EN ISO 3543:2002
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SIST EN ISO 3543:2002
INTERNATIONAL ISO
STANDARD 3543
Second edition
2000-12-15
Metallic and non-metallic coatings —
Measurement of thickness — Beta
backscatter method
Revêtements métalliques et non métalliques — Mesurage de l'épaisseur —
Méthode par rétrodiffusion des rayons beta
Reference number
ISO 3543:2000(E)
ISO 2000
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SIST EN ISO 3543:2002
ISO 3543:2000(E)
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© ISO 2000

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or mechanical, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISO's member body

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ii © ISO 2000 – All rights reserved
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SIST EN ISO 3543:2002
ISO 3543:2000(E)
Contents Page

Foreword.....................................................................................................................................................................iv

1 Scope ..............................................................................................................................................................1

2 Terms and definitions ...................................................................................................................................1

3 Principle..........................................................................................................................................................4

4 Apparatus .......................................................................................................................................................6

5 Factors relating to measurement uncertainty ............................................................................................6

6 Calibration of instruments ............................................................................................................................9

7 Measuring procedure ..................................................................................................................................10

8 Measurement uncertainty ...........................................................................................................................11

9 Test report ....................................................................................................................................................11

Annex A (informative) General information............................................................................................................13

© ISO 2000 – All rights reserved iii
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SIST EN ISO 3543:2002
ISO 3543:2000(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO

member bodies). The work of preparing International Standards is normally carried out through ISO technical

committees. Each member body interested in a subject for which a technical committee has been established has

the right to be represented on that committee. International organizations, governmental and non-governmental, in

liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical

Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 3.

Draft International Standards adopted by the technical committees are circulated to the member bodies for voting.

Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

International Standard ISO 3543 was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic

coatings, Subcommittee SC 2, Methods of inspection and coordination of test methods.

This second edition cancels and replaces the first edition (ISO 3543:1981), which has been technically revised.

Annex A of this International Standard is for information only.
iv © ISO 2000 – All rights reserved
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SIST EN ISO 3543:2002
INTERNATIONAL STANDARD ISO 3543:2000(E)
Metallic and non-metallic coatings — Measurement of thickness —
Beta backscatter method
1 Scope

WARNING Beta backscatter instruments used for the measurement of coating thicknesses use a number

of different radioactive sources. Although the activities of these sources are normally very low, they can

present a hazard to health, if incorrectly handled. Therefore, reference should be made to current

international and national standards, where these exist.

This International Standard specifies a method for the non-destructive measurement of coating thicknesses using

beta backscatter gauges. It applies to both metallic and non-metallic coatings on both metallic and non-metallic

substrates. To make use of this method, the atomic numbers or equivalent atomic numbers of the coating and the

substrate need to differ by an appropriate amount.

NOTE Since the introduction of the X-ray fluorescence method (ISO 3497), the beta backscatter method has been used

less and less for the measurement of coating thickness. However, because of its lower cost, it is still a very useful method of

measurement for many applications. In addition it has a wider measuring range.
2 Terms and definitions

For the purposes of this International Standard, the following terms and definitions apply.

2.1
radioactive decay

spontaneous nuclear transformation in which particles or gamma radiation are emitted or X-radiation is emitted

following orbital electron capture, or the nucleus undergoes spontaneous fission
[ISO 921:1997, definition 972]
2.2
beta particle

electron or positron which has been emitted by an atomic nucleus or neutron in a nuclear transformation

[ISO 921:1997, definition 81]
2.3
beta-emitting isotope
beta-emitting source
beta emitter
material, the nuclei of which emit beta particles

NOTE 1 It is possible to classify beta emitters by the maximum energy level of the particles that they release during their

disintegration.
NOTE 2 Table A.1 lists some isotopes used with beta backscatter gauges.
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SIST EN ISO 3543:2002
ISO 3543:2000(E)
2.4
electron-volt

unit of energy equal to the change in energy of an electron in passing through a potential difference of 1 V

�19
NOTE 1 1 eV = 1,602 19 � 10 J
[ISO 921:1997, definition 393]

NOTE 2 Since the electron-volt is too small for the energies encountered with beta particles, the mega-electron-volt (MeV) is

commonly used.
2.5
activity
disintegration rate

number of spontaneous nuclear disintegrations occurring in a given quantity of material during a suitably small

interval of time divided by that interval of time
[ISO 921:1997, definition 23]

NOTE 1 In beta backscatter measurements a higher activity corresponds to a greater emission of beta particles.

NOTE 2 The SI unit of activity is the becquerel (Bq). The activity of a radioactive element used in beta backscatter gauges is

4 4

generally expressed in microcuries (�Ci) (1 �Ci = 3,7 � 10 Bq, which represents 3,7 x 10 disintegrations per second).

2.6
radioactive half-life

time required for the activity to decrease to half its value by a single radioactive decay process

[ISO 921:1997, definition 975]
2.7
scattering

process in which a change in direction or energy of an incident particle or incident radiation is caused by a collision

with a particle or a system of particles
[ISO 921:1997, definition 1085]
2.8
backscatter

scattering as a result of which a particle leaves a body of matter from the same surface at which it entered

NOTE Radiations other than beta rays are emitted or backscattered by a coating and substrate and some of these can be

included in the backscatter measurement. In this International Standard the term “backscatter” is used to mean the total

radiation measured.
2.9
backscatter coefficient (of a body)
ratio of the number of particles backscattered to that entering the body

NOTE The value of R is independent of the activity of the isotope and of the measuring time.

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SIST EN ISO 3543:2002
ISO 3543:2000(E)
2.10
backscatter count
2.10.1
absolute backscatter count

number of particles backscattered during a fixed interval of time, and received by a detector

NOTE X depends on the activity of the isotope, the measuring time, the geometric configuration of the measuring system

and the properties of the detector. The count produced by the uncoated substrate is generally designated by X , and that of the

coating material by X . To obtain these values, both these materials have to be available with a thickness greater than the

saturation thickness (see 2.13).
2.10.2
normalized backscatter count

quantity that is independent of the activity of the isotope, the measuring time and the properties of the detector and

defined by the equation:
XX�
X �
XX�
where

X is the absolute backscatter count of the saturation thickness of the substrate material;

X is the absolute backscatter count of the saturation thickness of the coating material;

X is the absolute backscatter count of the coated specimen;
each of these counts being taken over the same interval of time
NOTE 1 The value of X is valid between 0 and 1.

NOTE 2 For simplicity, it is often advantageous to express the normalized backscatter count as a percentage by multiplying

X by 100.
2.11
normalized backscatter curve
curve obtained by plotting the coating thickness as a function of X
2.12
equivalent (apparent) atomic number

for a material, which can be an alloy or a compound, the atomic number of an element that has the same

backscatter coefficient R as the material
2.13
saturation thickness

minimum thickness of a material that, if exceeded, does not produce a change in backscatter

NOTE Figure A.1 shows saturation thickness, s, plotted as a function of density for different isotopes.

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SIST EN ISO 3543:2002
ISO 3543:2000(E)
2.14
sealed source

radioactive source sealed in a container or having a bonded cover, the container or cover being strong enough to

prevent contact with and dispersion of the radioactive material under the conditions of use and wear for which it

was designed
[ISO 921:1997, definition 1094]
NOTE Also referred to as “sealed isotope”.
2.15
aperture

opening of the mask abutting the test specimen and that determines the size of the area on which the coating

thickness is to be measured

NOTE This mask is also often referred to as a platen, an aperture platen or a specimen support.

2.16
source geometry

spatial arrangement of the source, the aperture and the detector, with respect to each other

2.17
dead time

time period during which a Geiger-Müller detector is unresponsive to the receipt of further beta particles

2.18
resolving time

recovery time of the Geiger-Müller detector tube and associated electronic equipment during which the counting

circuit is unresponsive to further pulses
2.19
basis material
basis metal
material upon which coatings are deposited or formed
[ISO 2080:1981, definition 134]
2.20
substrate
material upon which a coating is directly deposited

NOTE For a single or first coating the substrate is identical with the basis material; for a subsequent coating the

intermediate coating is the substrate
[ISO 2080:1981, definition 630]
3Principle

When beta particles impinge upon a material, a certain portion of particles is backscattered. This backscatter is

essentially a function of the atomic number of the material.

If the body has a surface coating, and if the atomic numbers of the substrate and of the coating material are

sufficiently different, the intensity of the backscatter will be between two limits: the backscatter intensity of the

substrate and that of the coating. Thus, with proper instrumentation and, if suitably displayed, the intensity of the

backscatter can be used for the measurement of mass per unit area of the coating, which, provided that it is of

uniform density, is directly proportional to the thickness, i.e., to the mean thickness within the measuring area.

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SIST EN ISO 3543:2002
ISO 3543:2000(E)

The curve expressing coating thickness versus beta backscatter intensity is continuous and can be subdivided into

three distinct regions as shown in Figure 1, on which the normalized count, X , is plotted on the x-axis, and the

logarithm of the coating thickness on the y-axis. In the range 0 u X u 0,3 the curve is essentially linear. In the

range 0,3u X u 0,8 the curve is nearly logarithmic; this means that, when drawn on semi-logarithmic graph paper,

as in Figure 1, the curve approximates a straight line. In the range 0,8u X u 1 the curve is nearly hyperbolic.

Key
1 Substrate with saturation thickness
2 Coating with saturation thickness
Approximately linear
Approximately logarithmic
Approximately hyperbolic
Figure 1 — Typical normalized backscatter curve
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SIST EN ISO 3543:2002
ISO 3543:2000(E)
4 Apparatus
4.1 Beta backscatter gauge, comprising:

a) a radiation source (isotope) emitting mainly beta particles having an energy appropriate to the coating

thickness to be measured;

b) a probe or measuring system with a range of apertures that limit the beta particles to the area of the test

specimen on which the coating thickness is to be measured, and containing a detector capable of counting the

number of backscattered particles, for example a Geiger-Müller counter (or tube);

c) a readout instrument where the intensity of the backscatter is displayed;

d) a readout instrument display, which can be in the form of a meter reading or a digital readout, either

proportional to the absolute count or to the absolute normalized count or to the coating thickness expressed

either in thickness units or in mass per unit area.
5 Factors relating to measurement uncertainty
5.1 Counting statistics

Radioactive decay takes place in a random manner. This means that, during a fixed time interval, the number of

beta particles backscattered will not always be the same. This gives rise to statistical errors inherent in radiation

counting. In consequence, an estimate of the counting rate based on a short counting interval (for example, 5 s)

can be appreciably different from an estimate based on a longer counting period, particularly if the counting rate is

low. To reduce the statistical error to an acceptable level, the counting interval has to be long enough to

accumulate a sufficient number of counts.

For counts normally made, the standard deviation,�, will closely approximate the square root of the absolute count,

that is � � X ; in 95 % of all cases, the true count will be within X � 2 �. To judge the significance of the precision,

it is often helpful to express the standard deviation as a percentage of the count, that is 100 XX/ , or 100 X.

Thus, a count of 100 000 will give a value 10 times more precise than that obtained with a count of 1 000.

Whenever possible, a counting interval shall be chosen that will provide a total count of at least 10 000, which

would correspond to a standard deviation of 1 % arising from the random nature of radioactive decay.

Direct-reading instruments are also subject to these statistical random errors. However, if these instruments do not

permit the display of the actual count rate, one way to determine the measuring precision is to make a large

number of repetitive measurements at the same location on the same coated specimen, and to calculate the

standard deviation by conventional means.

NOTE The precision of a thickness measurement by beta backscatter is always less than the precision described in 5.1, as

it also depends on the other factors described in 5.2 to 5.17.
5.2 Coating and substrate materials

As the backscatter intensity of a measurement depends on the atomic numbers of the substrate and of the coating,

the uncertainty of the measurement will depend to a large extent on the difference between these atomic numbers;

thus, with the same measuring parameters, the greater this difference, the more accurate the measurement will be.

As a guide, for most applications, the difference in atomic numbers should be at least 5. For materials with atomic

numbers below 20, this difference may be reduced to 25 % of the higher atomic number; for materials with atomic

numbers higher than 50, this difference should be at least 10 % of the higher atomic number. Most unfilled plastics

and related organic materials (for example photoresists) may be assumed to have an equivalent atomic number

close to 6.

NOTE Table A.2 gives the atomic numbers of some typical coatings and substrate materials.

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SIST EN ISO 3543:2002
ISO 354
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