Electrical insulating materials - Determination of the effects of ionizing radiation - Part 1: Radiation interaction and dosimetry

IEC 60544-1:2013 deals broadly with the aspects to be considered in evaluating the effects of ionizing radiation on all types of organic insulating materials. It also provides, for X-rays, gamma-rays, and electrons, a guide to dosimetry terminology, methods for dose measurements, testing carried out at irradiation facilities, evaluation and testing of material characteristics and properties, documenting the irradiation process. This edition includes the following significant technical changes with respect to the previous edition:
a) recent advances in simulation methods of radiation interaction with different matter enables the prediction of the energy-deposition profile in matter and design the irradiation procedure;
b) many new dosimetry systems have become available.

Matériaux isolants électriques - Détermination des effets des rayonnements ionisants - Partie 1: Interaction des rayonnements et dosimétrie

La CEI 60544-1:2013 traite de manière générale des aspects à envisager lors de l'évaluation des effets des rayonnements ionisants sur tous les types de matériaux isolants organiques. Elle fournit également pour les rayons X, les rayonnement gamma et les électrons, un guide de terminologie en dosimétrie, des méthodes de mesure des doses, des essais réalisés au niveau des dispositifs d'irradiation, relatif à l'évaluation et aux essais des caractéristiques et propriétés des matériaux, de documentation du phénomène d'irradiation. Cette édition inclut les changements techniques majeurs suivants par rapport à l'édition précédente:
a) des avancées récentes au niveau des méthodes de simulation de l'interaction des rayonnements avec des types de matière différents permettent de prédire le profil de dépôt d'énergie dans la matière et de concevoir la procédure d'irradiation;
b) de nombreux nouveaux systèmes de dosimétrie sont actuellement disponibles.

General Information

Status
Published
Publication Date
26-Jun-2013
Current Stage
PPUB - Publication issued
Start Date
27-Jun-2013
Completion Date
27-Jun-2013
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IEC 60544-1
Edition 3.0 2013-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical insulating materials – Determination of the effects of ionizing
radiation –
Part 1: Radiation interaction and dosimetry
Matériaux isolants électriques – Détermination des effets des rayonnements
ionisants –
Partie 1: Interaction des rayonnements et dosimétrie
IEC 60544-1:2013
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60544-1
Edition 3.0 2013-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Electrical insulating materials – Determination of the effects of ionizing
radiation –
Part 1: Radiation interaction and dosimetry
Matériaux isolants électriques – Détermination des effets des rayonnements
ionisants –
Partie 1: Interaction des rayonnements et dosimétrie
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX V
ICS 17.240; 29.035.01 ISBN 978-2-83220-894-6

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – 60544-1 © IEC:2013
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope ............................................................................................................................... 7

2 Normative references ....................................................................................................... 7

3 Terms and definitions ....................................................................................................... 7

4 Radiation-induced changes and their evaluation ............................................................... 9

4.1 General ................................................................................................................... 9

4.2 Permanent changes ................................................................................................ 9

4.3 Environmental conditions and material geometry ..................................................... 9

4.4 Post-irradiation effects ............................................................................................ 9

4.5 Temporary effects ................................................................................................... 9

5 Facilities for irradiation of material samples for evaluation of properties ......................... 10

5.1 General ................................................................................................................. 10

5.2 Gamma-ray irradiators ........................................................................................... 10

5.3 Electron-beam irradiators ...................................................................................... 10

5.4 X-ray (Bremsstrahlung) irradiators ......................................................................... 11

6 Dosimetry methods ......................................................................................................... 11

6.1 General ................................................................................................................. 11

6.2 Absolute dosimetry methods .................................................................................. 12

6.2.1 Gamma-rays .............................................................................................. 12

6.2.2 Electron beams ......................................................................................... 12

6.3 Dosimetry systems ................................................................................................ 12

6.3.1 Reference standard dosimetry systems ..................................................... 12

6.3.2 Routine dosimetry systems ........................................................................ 13

6.3.3 Measurement uncertainty .......................................................................... 14

6.3.4 Dosimeter calibration ................................................................................. 15

6.3.5 Dosimeter selection ................................................................................... 15

7 Characterization of irradiation facilities ........................................................................... 16

8 Dose mapping of samples for test ................................................................................... 16

8.1 Charged particle equilibrium .................................................................................. 16

8.2 Depth-dose distribution (limitations) ...................................................................... 16

9 Monitoring of the irradiation ............................................................................................ 17

Annex A (informative) Radiation chemical aspects in interaction and dosimetry ................... 18

Bibliography .......................................................................................................................... 31

Figure A.1 – Absorbed dose as a function of thickness ......................................................... 19

Figure A.2 – Absorber thickness for charged-particle equilibrium as a function of

23 -3

energy for a material with an electron density of 3,3 × 10 cm (water)............................... 20

Figure A.3 – Thickness of water (1 g/cm ) as a function of photon energy for a given

attenuation of unidirectional X-ray or γ-ray radiation ............................................................. 21

Figure A.4 – Typical depth-dose distribution in a homogeneous material obtained with

electron accelerators for radiation processing ....................................................................... 25

Figure A.5 – Example of calculated results of energy deposition function, I(z′), for a

slab layer of polyethylene exposed to 1 MeV electron ........................................................... 25

Figure A.6 – Example of calculated results of energy deposition function, I(z′), for

typical organic insulators exposed to 1 MeV electron ............................................................ 26

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60544-1 © IEC:2013 – 3 –

Figure A.7 – Two methods of arranging the irradiation samples in order to take into

account the typical depth-dose distributions .......................................................................... 27

Figure A.8 – Methods of arranging the irradiation samples for measuring electron

depth-dose distributions with a stack of slab insulating materials and wedge-shape

insulating materials ............................................................................................................... 28

Figure A.9 – Scheme of radiation effects of polymers............................................................ 29

Table 1 – Examples of reference standard dosimeters .......................................................... 13

Table 2 – Examples of routine dosimeter systems ................................................................. 14

Table A.1 – Electron mass collision stopping powers, S/ρ (MeV cm /g) ................................. 23

Table A.2 – Photon mass energy absorption coefficients, µ /ρ (cm /g) .............................. 24

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– 4 – 60544-1 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 1: Radiation interaction and dosimetry
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

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governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

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

International Standard IEC 60544-1 has been prepared by IEC technical committee 112:

Evaluation and qualification of electrical insulating materials and systems.

This third edition cancels and replaces the second edition published in 1994 and constitutes a

technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

a) recent advances in simulation methods of radiation interaction with different matter

enables the prediction of the energy-deposition profile in matter and design the irradiation

procedure;
b) many new dosimetry systems have become available.
---------------------- Page: 6 ----------------------
60544-1 © IEC:2013 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
112/254/FDIS 112/262/RVD

Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts in the IEC 60544 series, published under the general title Electrical insulating

materials – Determination of the effects of ionizing radiation, can be found on the IEC website.

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
---------------------- Page: 7 ----------------------
– 6 – 60544-1 © IEC:2013
INTRODUCTION

The establishment of suitable criteria for the evaluation of the radiation resistance of

insulating materials is very complex, since such criteria depend upon the conditions under

which the materials are used. For instance, if an insulated cable is flexed during a refuelling

operation in a reactor, the service life will be that time during which the cable receives a

radiation dose sufficient to reduce to a specified value one or more of the relevant mechanical

properties. Temperature of operation, composition of the surrounding atmosphere and the

time interval during which the total dose is received (dose rate or flux) are important factors

which also determine the rate and mechanisms of chemical changes. In some applications,

temporary changes may be the limiting factor.

Given this, it becomes necessary to define the radiation fields in which materials are exposed

and the radiation dose subsequently absorbed by the material. It is also necessary to

establish procedures for testing the mechanical and electrical properties of materials which

will define the radiation degradation and link those properties with application requirements in

order to provide an appropriate classification system.
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60544-1 © IEC:2013 – 7 –
ELECTRICAL INSULATING MATERIALS –
DETERMINATION OF THE EFFECTS OF IONIZING RADIATION –
Part 1: Radiation interaction and dosimetry
1 Scope

This part of IEC 60544 deals broadly with the aspects to be considered in evaluating the

effects of ionizing radiation on all types of organic insulating materials. It also provides, for X-

rays, γ-rays, and electrons, a guide to
– dosimetry terminology,
– methods for dose measurements,
– testing carried out at irradiation facilities,
– evaluation and testing of material characteristics and properties,
– documenting the irradiation process.

Dosimetry that might be carried out at locations of use of the material is not described in this

standard.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.

IEC 60544-2, Electrical insulating materials – Determination of the effects of ionizing radiation

on insulating materials – Part 2: Procedures for irradiation and test

IEC 60544-4, Electrical insulating materials – Determination of the effects of ionizing radiation

– Part 4: Classification system for service in radiation environments
3 Terms and definitions

For the purposes of this document, the terms and definitions in ICRU Report 33 [1] . as well

as the following definitions apply.
3.1
exposure

measure of an electromagnetic radiation field (X- or γ-radiation) to which a material is

exposed

Note 1 to entry: The exposure is the quotient obtained by dividing dQ by dm, where dQ is the absolute value of

the total charge of the ions of one sign produced in the air when all of the electrons (and positrons) liberated by

photons in air of mass dm are completely stopped in air:
—————————
References in square brackets refer to the Bibliography.
---------------------- Page: 9 ----------------------
– 8 – 60544-1 © IEC:2013
X = (1)

The SI unit of exposure is the coulomb (C) per kilogram: C/kg. The old unit is the roentgen R:

1 R = 2,58 × 10 C/kg.

The exposure thus describes the effect of an electromagnetic field on matter in terms of the ionization that the

radiation produces in a standard reference material, air.
3.2
electron charge fluence

quotient obtained by dividing dQ by dA, where dQ is the electron charge impinging during the

time t on the area dA:
Q = (2)
d A
3.3
electron current density

quotient obtained by dividing dQ′ by dt, where dQ′ is the electron charge fluence during the

time interval dt:
dQ′ d Q
j = = (3)
dt d A dt
3.4
absorbed dose

measure of the energy imparted to the irradiated material, regardless of the nature of the

radiation field

Note 1 to entry: The absorbed dose D is the quotient obtained by dividing d ε by dm where d ε is the mean

energy imparted by ionizing radiation to matter of mass dm:
D = (4)
The SI unit is the gray (Gy). The old unit is the rad:
-1 2
1 Gy = 1 J × kg (= 10 rad).

Since this definition does not specify the absorbing material, the gray can be used only with reference to a specific

material. The absorbed dose is determined in part by the composition of the irradiated material. When exposed to

the same radiation field, therefore, different materials usually receive different absorbed doses.

Note 2 to entry: For purposes of dosimetry, it has been found convenient to specify dose in terms of dose to water.

The dose to other materials can be found by applying cavity theory.
3.5
absorbed dose rate

quotient obtained by dividing dD by dt, where dD is the increment of absorbed dose in the

time interval dt:
D = (5)
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60544-1 © IEC:2013 – 9 –
The SI unit of absorbed dose rate is the gray per second:
-1 -1 2 -1 -1
1 Gy × s = 1 W × kg (= 10 rad × s = 0,36 Mrad × h )
4 Radiation-induced changes and their evaluation
4.1 General

Although the various types of radiation interact with matter in different ways, the primary

process is the production of ions and electrically excited states of molecules which, in turn,

may lead to the formation of free radicals. The technique to detect ions, excited states and

radicals (short-lived intermediate species) are briefly described in Clause A.4. Radiation-

generated mobile electrons, which become trapped at sites of low potential energy, are also

produced. The first phenomenon leads to permanent chemical, mechanical, and electrical

changes of the material; the second results in temporary electrical changes in performance [2].

4.2 Permanent changes

In polymeric materials, the formation of free radicals during irradiation leads to scission and

cross-linking processes that modify the chemical structure of the insulation, generally leading

to deterioration of the mechanical properties. This mechanical deterioration frequently gives

rise to significant electrical property changes. However, important electrical property changes

sometimes occur before mechanical degradation becomes serious. For example, a change in

dissipation factor or in permittivity might become serious for the reliable functioning of a

resonant circuit. The extent of scission and cross-linking processes depends on the absorbed

dose, the absorbed dose rate, the material geometry and the environmental conditions

present during the irradiation. Because the free radicals sometimes decay slowly, there may

also be post-irradiation effects.
4.3 Environmental conditions and material geometry
Environmental conditions and test specimen geometry shall be well controlled and

documented during the measurement of radiation effects. Important environmental parameters

include temperature, reactive medium, and mechanical and electrical stresses present during

the irradiation. If air is present, the irradiation time (flux and dose rate) has also been

demonstrated to be a very important experimental parameter because of oxygen diffusion

effects and hydroperoxide breakdown rate constants. Both factors are time dependent. The

conditions that influence oxygen diffusion and equilibrium concentrations in the polymer shall

be controlled. These include: temperature, oxygen pressure, material geometry and the time

during which the dose is applied.

If the effect of simultaneous stresses, e.g. radiation at high temperature, is simulated by

sequential stressing, other results are to be expected. Further, there can be differences in

results if the sample is first irradiated and then heat aged or vice versa.
4.4 Post-irradiation effects

In organic polymers, there may be post-irradiation effects due to the gradual decay of various

reactants, such as residual free radicals. Due allowance shall be made for this type of

behaviour in any evaluation procedure. The tests shall be made at recorded intervals after

irradiation, maintaining specimen storage in a standard laboratory atmosphere. The reaction

of oxygen with residual free radicals can cause further degradation.
4.5 Temporary effects

4.5.1 Performing measurements during irradiation is not within the scope of this part

of IEC 60544. Despite this, some basic aspects will be discussed briefly. The temporary

effects appear primarily as changes in electrical properties such as induced conductivity, both

during and for some time after irradiation. Hence, measurement of the induced conductivity

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– 10 – 60544-1 © IEC:2013

could be used as an evaluation property to determine the temporary radiation effects. These

effects are primarily dose-rate dependent.

4.5.2 Experience has shown that the induced conductivity is usually not quite proportional

 

to the absorbed dose rate D, but varies as D , where α is smaller than unity. Hence, the

radiation sensitivity is described by the relation:
 α
σ = kD (6)

To determine k and α, at least two measurements are needed. A further complication

comes from the fact that k and α also depend on the integrated dose absorbed by the sample.

The measurement of the induced conductivity is actually quite delicate, since photoelectrons

and Compton electrons in the electrode materials will tend to perturb the intrinsic induced

current of the specimen. Ionic currents through the ionized atmosphere will also introduce

errors in the measurement if they are not eliminated. Experimental procedures eliminating

most of the disturbing effects, while remaining relatively simple, shall be defined.

NOTE It is convenient to use a simple figure such as the induced conductivity σ or σ /σ , its ratio to the dark

i i o

conductivity σ measured in the same experimental conditions, per unit dose rate to characterize the sensitivity of

the materials to temporary effects.
5 Facilities for irradiation of material samples for evaluation of properties
5.1 General

Irradiation of material samples for evaluation of properties shall be performed at irradiation

facilities that have undergone installation qualification, operational qualification and

performance qualification, see e.g. ISO 11137 [3].
Three principal types of radiation sources are used:
60 137
• gamma radiation from radionuclides such as Co (1,25 MeV) and Cs (0,66 MeV);
• electrons from accelerators;
• X-rays generated from accelerated electrons.

The design and properties of an irradiation facility have implications for absorbed dose

distribution in the samples and attainable absorbed dose range. Major considerations in the

design of an irradiation facility are the uniformity of the distribution of absorbed dose in the

given product, efficient utilization of radiation energy.
5.2 Gamma-ray irradiators

Large capacity gamma radiation facilities usually use Co as the radiation source. The

sources are often in the form of individual source capsules arranged in an array to maximize

the volume available for irradiations. The dose rates that are available will be dependent on

the distance from the sources at which the samples are placed. Typically, dose rates in the

range 10 kGy/h (2,78 Gy/s) down to 1 Gy/h (0,278 mGy/s) are possible. This covers the range

of dose rates that are of particular interest for materials degradation testing.
5.3 Electron-beam irradiators

Electron beam irradiators use accelerators that generate electron beam in the energy-range of

300 KeV – 10 MeV. At present, various types of accelerating procedures are available;

examples include electro-static type and high-frequency (radio-frequency) type. With respect

to radiation resistance testing, electro-static type of (0,5 – 3 )MeV is widely used. In an

electro-static accelerating system, thermo-electrons are emitted from a cathode and the

---------------------- Page: 12 ----------------------
60544-1 © IEC:2013 – 11 –

emitted electrons are accelerated with high voltage applied between electrodes. Electron

beams are electro-magnetically scan
...

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