Metallic and non-metallic coatings - Measurement of thickness - Beta backscatter method (ISO 3543:1981)

Metallische und nichtmetallische Schichten - Dickenmessung - Betarückstreu-Verfahren (ISO 3543:1981)

Die vorliegende Internationale Norm legt das Verfahren der zerstörungsfreien Messung der Dicke von Schichten nach dem Betarückstreuverfahren fest. Sie gilt für metallische und nichtmetallische Grundwerkstoffe. Um das Verfahren anzuwenden, müssen sich die Ordnungsgzahlen 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 3543:1981)

Kovinske in nekovinske prevleke - Merjenje debeline – Metoda z beta povratnim sipanjem (ISO 3543:1981)

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SIST EN ISO 3543:1999
Kovinske in nekovinske prevleke - Merjenje debeline – Metoda z beta povratnim
sipanjem (ISO 3543:1981)
Metallic and non-metallic coatings - Measurement of thickness - Beta backscatter
method (ISO 3543:1981)

Metallische und nichtmetallische Schichten - Dickenmessung - Betarückstreu-Verfahren

(ISO 3543:1981)

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

rétrodiffusion des rayons beta (ISO 3543:1981)
Ta slovenski standard je istoveten z: EN ISO 3543:1994
25.220.20 Površinska obdelava Surface treatment
25.220.40 Kovinske prevleke Metallic coatings
SIST EN ISO 3543:1999 en

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

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SIST EN ISO 3543:1999
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SIST EN ISO 3543:1999
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SIST EN ISO 3543:1999
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SIST EN ISO 3543:1999
International Standard


Metallic and non-metallic coatings - Measurement of
thickness -
Beta backscatter method
Revetements m&alfiques et non m&alliques - Mesurage de l’&paisseur -
Methode par r&rodiffusion des rayons b&a
First edition - 1981-07-15
UDC 669.058 : 531.717 : 537.533.74
Ref. No. ISO3543-1981 (E)
Descriptors : coatings, metal coatings, non metallic coatings,
dimensional measurement, thickness, non destructive tests, beta backscatter
Price based on 9 pages
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SIST EN ISO 3543:1999

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

national Standards institutes (ISO member bodies). The work of developing Interna-

tional Standards is carried out through ISO technical committees. Every member body

interested in a subject for which a technical committee has been set up 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.

Draft International Standards adopted by the technical committees are circulated to

the member bodies for approval before their acceptance as International Stan-
dards by the ISO Council.
International Standard ISO 3543 was developed by Technical Committee ISO/TC 107,

M’eta/ic and other non-organic coatings, and was circulated to the member bodies in

May 1978.
lt has been approved by the member bodies of the following countries :
Australia India Sweden
Czechoslovakia Switzerland
Egypt, Arab Rep. of Italy United Kingdom
France Japan USA
Germany, F. R. Mexico USSR
Hungary South Africa, Rep. of
No member body expressed disapproval of the document.
0 International Organkation for Standardkation, 1981
Printed in Switzerland
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SIST EN ISO 3543:1999
ISO 3543-1981 IE)
Metallic and non-metallic coatings - Measurement of
thickness - Beta backscatter method
2.4 electron-volt : A unit of energy equal to the Change in
1 Scope and field of application
energy of an electron in passing through a potential differente
of 1 V. (1 eV = 1,602 10 x 10-19 J)”
This International Standard specifies a method for the non-
destructive measurement of coating thicknesses using beta

backscatter gauges. lt applies to both metallic and non-metallic Since this unit is too small for the energies encountered with

beta particles, the mega-electronvolt (MeV) is commonly used.
coatings on both metallic and non-metallic Substrates. To
employ this method, the atomic numbers or equivalent atomic
numbers of the coating and the Substrate must differ by an
appropriate amount.
2.5 activity : The number of spontaneous nuclear
disintegrations occurring in a given quantity of material during
CAUTION - Beta backscatter instruments used for the
a suitably small interval of time divided by that interval of time.*
measurement of coating thicknesses employ a number of
different radioactive sources. Although the activities of
Therefore, in beta backscatter measurements, a higher activity
these sources are normally very low, they tan present a
corresponds to a greater emission of beta particles.
hazard to health, if incorrectly handled. Therefore, all
rules and regulations of local or national authorities must
The SI unit of activity is the becquerel (Bq). The activity of a
be observed.
radioactive element used in beta backscatter gauges is gener-
ally expressed in microcuries (PCi) (1 PCi = 3,7 x 104 Bq,
which represents 3,7 x 104 disintegrations per second).
2 Def initions
For the purpose of this International Standard, the following
2.6 half-life, radioactive : For a Single radioactive decay
definitions apply.
process, the time required for the activity to decrease to half its
value by that process.*
2.1 radioactive decay : A spontaneous nuclear transforma-
tion in which particles or gamma radiation are emitted or

X-radiation is emitted following orbital electron Capture or in 2.7 stattering : A process in which a Change in direction or

which the nucleus undergoes spontaneous fission.” energy of an incident particle or incident radiation is caused by

a collision with a particle or a System of particles.”
2.2 beta particle : An electron, of either positive or negative
Charge, which has been emitted by an atomic nucleus or
2.8 backscatter : Stattering as a result of which a particle
neutron in a nuclear transformation. *
leaves a body of matter from the same surface at which it
2.3 beta-emitting isotope; beta-emitting Source; beta
emitter : A material the nuclei of which emit beta particles.
NOTE - Radiations other than beta rays are emitted or backscattered
by a coating and Substrate and some of these may be included in the
lt is possible to classify beta emitters by the maximum energy
backscatter measurement. Whenever the term “backscatter” is used in
level of the particles which they release during their disintegra-
this International Standard, it is to be assumed that reference is made
to the total radiation measured.
* Definition taken from ISO 921, Nuclear energy glossary.
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SIST EN ISO 3543:1999
ISO 3543-1981 (El
2.14 sealed Source : P radioactive Source sealed in a con-
2.9 backscatter coefficient, R (sf a body) : The ratio of

the number of particles backscattered to that entering the tainer or having a bonded cover, the Container or cover being

strong enough to prevent
body. contact with and dispersion of the
radioactive material under the conditions of use and wear for

This number R is independent of the activity of the isotope and which it was designed.”

of the measuring time.
(Also called sealed isotope.)
2.10 backscatter count :
2.15 aperture : The opening of the mask abutting the test
2.10.1 absolute backscatter count, X : The number of par-
specimen, which determines the size of the area on which the
ticles backscattered during a fixed interval of time, and received
coating thickness is to be measured. (This mask is also often
by a detector.
referred to as a platen, an aperture platen, or a specimen sup-
X will, therefore, depend on the activity of the isotope, the
measuring time, the geometric configuration of the measuring
System, and the properties of the detector. The count pro-
: The spatial arrangemen
2.16 Source geometry t of the
duced by the uncoated Substrate is generally designated by XO,
Source, , the aperture, and the detector, with respect to each
and that of the coating material by X,. To obtain these values,
it is necessary that both these materials are available with a
thickness greater than the Saturation thickness (see 2.13).
2.17 dead time : The time period during which a Geiger-
2.10.2 normalized backscatter count, x, : A quantity
Müller tube is unresponsive to the receipt of further beta par-
which is independent of the activity of the isotope, the measur-
ing time, and the properties of the detector, and defined by the
equation :
2.18 resolving time : The recovery time of the Geiger-
x - x.
Müller tubes and associated electronie equipment during which
x, = -
the counting circuit is unresponsive to further pulses.
xs - xo
X0 is the absolute backscatter count of the Saturation 3 Principle
thickness of the Substrate material;
When beta particles impinge upon a material, a certain Portion

Xs is the absolute backscatter count of the Saturation of them is backscattered. This backscatter is essentially a func-

tion of the atomic number of the material.
thickness of the coating material;
If the body has a surface coating, and if the atomic numbers of
X is the absolute backscatter count of the coated specimen;
the Substrate and of the coating material are sufficiently dif-
ferent, the intensity sf the backscatter will be between two
each of these counts being taken over the same interval of
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 tan be used for the
For simplicity, it is often advantageous to express the normal-
measurement of mass per unit area of the coating which, pro-
ized backscatter count as a percentage by multiplying x, by
vided that it is of uniform density, is directly proportional to the
thickness, that is, to the mean thickness within the measuring
2.11 normalized backscatter curve : The curve obtained
by plotting the coating thickness as a function of x,.
The curve expressing coating thickness versus beta backscatter
intensity is continuous and tan be subdivided into three distinct
2.12 equivalent [apparentl atomic number : For a
regions, as shown in figure 1, on which the normalized count,
material, which tan be an alloy or a compound, the atomic
x,, is plotted on the X-axis, and the logarithm of the coating
number of an element which has the same backscatter coeffic-
thickness on the Y-axis. In the range 0 ient R as the material.
essentially linear. In the range 0,35 nearly logarithmic; this means that, when drawn on semi-
logarithmic graph Paper, as in figure 1, the curve approximates
: The minimum thickness of a
2.13 Saturation thickness
a straight line. In the range 0,85 material which produces a backscatter which is not changed
when the thickness is increased. (See also annex C.)
* Definition taken
from ISO 921, Nuclear energ y glossary.
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SIST EN ISO 3543:1999
ISO 35434981 (El
4 5.2 Coating and Substrate materials

In general, a beta backscatter gauge will comprise : As the backscatter intensity of a measurement depends on the

atomic numbers of the Substrate and the coating, the accuracy

a) a radiation Source (isotope) emitting mainly beta par- of the measurement will depend to a large degree on the dif-

ticles having an energy appropriate to the coating thickness ference between these atomic numbers; thus, with the same

to be measured; measuring Parameters, the greater this differente, the more
accurate the measurement will be.
a probe or measuring System with a range of apertures

that limit the beta particles to the area of the test specimen As a rule of thumb, for most applications, it tan be stated that

the differente in atomic numbers should be at least 5. For
on which the coating thickness is to be measured, and con-
materials with atomic numbers below 20, this differente may be
taining a detector capable of counting the number of
reduced to 25 % of the higher atomic number; for materials
backscattered pat-ticles, for example a Geiger-Müller
with atomic numbers higher than 50, this differente should be
counter (or tube);
at least 10 % of the higher atomic number. Most unfilled
plastics and related organic materials (for example
c) a readout instrument where the intensity of the
photoresists) may be assumed to have an equivalent atomic
backscatter is displayed. The display, which tan be in the
number close to 6.
form of a meter reading or a digital readout, is either propor-
tional to the absolute count, or to the absolute normalized

count, or to the coating thickness expressed either in (Annex B gives atomic numbers of commonly used coating and

thickness units or in mass per unit area. Substrate materials.)
5.3 Aperture
Despite the collimated nature of the sources used in commer-
5 Factors relating to accuracy
cial backscatter gauges, the backscatter recorded by the detect-
or is, nearly always, the sum of the backscatter produced by
5.1 Counting statistics
the test specimen exposed through the aperture and that of the
specimen support. lt is, therefore, advantageous to use for the
Radioactive decay takes place in a random manner. This means
platen construction a material with a low atomic number, and
that, during a fixed time interval, the number of beta particles
to select the largest aperture possible. However, measuring
backscattered will not always be the Same. This gives rise to
errors will still occur if the edges of the aperture opening are
statistical errors inherent in radiation counting. In conse-
worn or damaged, or if the test specimen does not properly
quence, an estimate of the counting rate based on a short
contact these edges.
counting interval (for example, 5 s) may be appreciably dif-
ferent from an estimate based on a longer counting period, par-
Because the measuring area on the test specimen has to be
ticularly if the counting rate is low. To reduce the statistical
constant to prevent the introduction of another variable,
error to an acceptable level, it is necessary to use a counting
namely the dimensions of the test specimen, the aperture shall
interval long enough to accumulate a sufficient number of
be smaller than the area of the surface on which the measure-
ment is made.
For counts normally made, the Standard deviation (0) will
closely approximate the Square root of the absolute count, that
is o = J X; in 95 % of all cases, the true count will be within X
5.4 Coating thickness
rt 2 CL To judge the significance of the precision, it is often
helpful to express the Standard deviation as a percentage of the
5.4.1 In the logarithmic range, the rer’ative measuring error is
count, that is 100 ,/XlX, or lOO/JX. Thus, a count of
nearly constant, and has its smallest value.
100 000 will give a value ten times more precise than that ob-
tained with a count of 1 000. Whenever possible, a counting in-
terval sha II be
Chosen that will provide a total count of at least
5.4.2 In the linear range, the absolute measuring error, ex-
10ooo,w hich would correspond to a Standard deviation of 1 %
pressed in mass per unit area or thickness, is nearly constant,
arising from the random nature of radioactive decay.
which means that as the coating thickness decreases, the
relative measuring error increases. At, or near, xn = 0,35, the
Direct reading instruments are also subject to these statistical
relative errors of the linear and logarithmic ranges are about the
random errors. However, if these instruments do not permit the
Same. This means that the relative error at this Point may, for all
display of the actual count rate, one way to determine the
practical purposes, be used to calculate the absolute error over
measuring precision is to make a large number of repetitive
the entire linear range.
measurements at the same location on the same coated
specimen, and to calculate the Standard deviation by conven-
tional means.
5.4.3 In the hyperbolic range, the measuring error is always
large, because a small Variation in the intensity of the beta
IMPORTANT NOTE - The precision of a thickness measurement by

beta backscatter is always less than the precision described above, backscatter will produce a large Variation in the measured value

inasmuch as it also depends on other factors which are listed below.
of coating thickness.
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SIST EN ISO 3543:1999

.5 Resolwing time od the detector mine this range Bor each Substrate thickness, without having

actual Standards. lf they are no% available from the manufac-
5ecause of the dead time of the Geiger-Müller tube (sec 2.171,
turer, this range has to be determined experimentally.
the count indicated by the readout instrument is always less
than the actual number of backscattered beta particles th

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