SIST EN ISO 6980-2:2025

SLOVENSKI STANDARD
01-december-2025
Jedrska energija - Referenčno sevanje delcev beta - 2. del: Osnove kalibracije,
povezane z osnovnimi veličinami, ki označujejo polje sevanja (ISO 6980-2:2023)
Nuclear energy - Reference beta-particle radiation - Part 2: Calibration fundamentals
related to basic quantities characterizing the radiation field (ISO 6980-2:2023)
Kernenergie - Beta-Referenzstrahlung - Teil 2: Kalibriergrundlagen für Basisgrößen, die
das Strahlungsfeld charakterisieren (ISO 6980-2:2023, einschließlich korrigierte Fassung
2024-03)
Énergie nucléaire - Rayonnement bêta de référence - Partie 2: Concepts d'étalonnage
en relation avec les grandeurs fondamentales caractérisant le champ de rayonnement
(ISO 6980-2:2023)
Ta slovenski standard je istoveten z: EN ISO 6980-2:2025
ICS:
17.240 Merjenje sevanja Radiation measurements
27.120.01 Jedrska energija na splošno Nuclear energy in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 6980-2
EUROPEAN STANDARD
NORME EUROPÉENNE
September 2025
EUROPÄISCHE NORM
ICS 17.240
English Version
Nuclear energy - Reference beta-particle radiation - Part 2:
Calibration fundamentals related to basic quantities
characterizing the radiation field (ISO 6980-2:2023,
including corrected version 2024-03)
Énergie nucléaire - Rayonnement bêta de référence - Kernenergie - Beta-Referenzstrahlung - Teil 2:
Partie 2: Concepts d'étalonnage en relation avec les Kalibriergrundlagen für Basisgrößen, die das
grandeurs fondamentales caractérisant le champ de Strahlungsfeld charakterisieren (ISO 6980-2:2023,
rayonnement (ISO 6980-2:2023, y compris version einschließlich korrigierte Fassung 2024-03)
corrigée 2024-03)
This European Standard was approved by CEN on 22 September 2025.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 6980-2:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 6980-2:2023 including corrected version 2024-03 has been prepared by Technical
Committee ISO/TC 85 "Nuclear energy, nuclear technologies, and radiological protection” of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 6980-2:2025 by
Technical Committee CEN/TC 430 “Nuclear energy, nuclear technologies, and radiological protection”
the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by March 2026, and conflicting national standards shall
be withdrawn at the latest by March 2026.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 6980-2:2023, including corrected version 2024-03 has been approved by CEN as
International
Standard
ISO 6980-2
Third edition
Nuclear energy — Reference beta-
2023-11
particle radiation —
Corrected version
Part 2:
2024-03
Calibration fundamentals related to
basic quantities characterizing the
radiation field
Énergie nucléaire — Rayonnement bêta de référence —
Partie 2: Concepts d'étalonnage en relation avec les grandeurs
fondamentales caractérisant le champ de rayonnement
Reference number
ISO 6980-2:2023(en) © ISO 2023

ISO 6980-2:2023(en)
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 6980-2:2023(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms and reference and standard test conditions . 3
5 Calibration and traceability of reference radiation fields . 6
6 General principles for calibration of beta‑particle radiation fields . 6
6.1 General .6
6.2 Scaling to derive equivalent thicknesses of various materials .6
6.3 Characterization of the radiation field in terms of penetrability.7
7 Calibration procedures using an extrapolation chamber . 8
7.1 General .8
7.2 Determination of the reference beta-particle absorbed-dose rate .8
8 Calibration with ionization chambers .10
9 Measurements at non-perpendicular incidence . 10
10 Uncertainties . 10
Annex A (normative) Reference conditions and standard test conditions . 19
Annex B (informative) Extrapolation chamber measurements .21
Annex C (informative) Extrapolation chamber measurement correction factors .25
Annex D (informative) Example of an uncertainty analysis .37
Bibliography . 41

iii
ISO 6980-2:2023(en)
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.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO document should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 2, Radiological protection.
This third edition of ISO 6980-2 cancels and replaces ISO 6980-2:2022, of which it constitutes a minor
revision.
The main changes are as follows:
— editorial changes throughout the document.
A list of all the parts in the ISO 6980 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
This corrected version of ISO 6980-2:2023 incorporates the following corrections:
— several wrong values have been corrected in Table C.7.

iv
ISO 6980-2:2023(en)
Introduction
ISO 6980 series covers the production, calibration, and use of reference beta-particle radiation fields for
the calibration of dosemeters and dose-rate meters for protection purposes. This document describes the
procedures for the determination of absorbed dose rate to a reference depth of tissue from reference beta
particle radiation fields. ISO 6980-1 describes methods of production and characterization of the reference
radiation. ISO 6980-3 describes procedures for the calibration of dosemeters and dose-rate meters and the
determination of their response as a function of beta-particle energy and angle of beta-particle incidence.
For beta particles, the calibration and the determination of the response of dosemeters and dose-rate
meters is essentially a three-step process. First, the basic field quantity, absorbed dose to tissue at a depth
of 0,07 mm (and optionally also at a depth of 3 mm) in a tissue-equivalent slab geometry is measured at
the point of test, using methods described in this document. Then, the appropriate operational quantity is
derived by the application of a conversion coefficient that relates the quantity measured (reference absorbed
dose) to the selected operational quantity for the selected irradiation geometry. Finally, the reference point
of the device under test is placed at the point of test for the calibration and determination of the response
of the dosemeter. Depending on the type of dosemeter under test, the irradiation is either carried out on a
phantom or free-in-air for personal and area dosemeters, respectively. For individual and area monitoring,
this document describes the methods and the conversion coefficients to be used for the determination of the
response of dosemeters and dose-rate meters in terms of the ICRU operational quantities, i.e., directional
dose equivalent, H′(0,07;Ω) and H′(3;Ω), as well as personal dose equivalent, H (0,07) and H (3).
p p
v
International Standard ISO 6980-2:2023(en)
Nuclear energy — Reference beta-particle radiation —
Part 2:
Calibration fundamentals related to basic quantities
characterizing the radiation field
1 Scope
This document specifies methods for the measurement of the absorbed-dose rate in a tissue-equivalent slab
phantom in the ISO 6980 reference beta-particle radiation fields. The energy range of the beta-particle-
emitting isotopes covered by these reference radiations is 0,22 MeV to 3,6 MeV maximum beta energy
corresponding to 0,07 MeV to 1,2 MeV mean beta energy. Radiation energies outside this range are beyond
the scope of this document. While measurements in a reference geometry (depth of 0,07 mm or 3 mm at
perpendicular incidence in a tissue-equivalent slab phantom) with an extrapolation chamber used as
primary standard are dealt with in detail, the use of other measurement systems and measurements in other
[5]
geometries are also described, although in less detail. However, as noted in ICRU 56 , the ambient dose
equivalent, H*(10), used for area monitoring, and the personal dose equivalent, H (10), as used for individual
p
monitoring, of strongly penetrating radiation, are not appropriate quantities for any beta radiation, even
that which penetrates 10 mm of tissue (E > 2 MeV).
max
This document is intended for those organizations wishing to establish primary dosimetry capabilities for
beta particles and serves as a guide to the performance of dosimetry with an extrapolation chamber used as
primary standard for beta-particle dosimetry in other fields. Guidance is also provided on the statement of
measurement uncertainties.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 29661, Reference radiation fields for radiation protection — Definitions and fundamental concepts
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated terms (VIM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 29661, ISO/IEC Guide 99 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
extrapolation curve
curve given by a plot of the corrected ionization current versus the extrapolation chamber depth

ISO 6980-2:2023(en)
3.2
ionization chamber
ionizing radiation detector consisting of a chamber filled with a suitable gas (almost always air), in which
an electric field, insufficient to induce gas multiplication, is provided for the collection at the electrodes of
charges associated with the ions and electrons produced in the measuring volume of the detector by ionizing
radiation
Note 1 to entry: The ionization chamber includes the measuring volume, the collecting and polarizing electrodes, the
guard electrode, if any, the chamber wall, the parts of the insulator adjacent to the sensitive volume and any additional
material placed in front of the ionization chamber to simulate measurement at depth.
3.3
extrapolation (ionization) chamber
ionization chamber (3.2) capable of having an ionization volume which is continuously variable to a
vanishingly small value by changing the separation of the electrodes and which allows the user to extrapolate
the measured ionization density to zero collecting volume
3.4
ionization density
measured ionization per unit volume of air
3.5
leakage current
Ι
B
ionization chamber (3.2) current measured at the operating bias voltage in the absence of radiation
3.6
maximum beta energy
E
max
highest value of the energy of beta particles emitted by a particular radionuclide which can emit one or
several continuous spectra of beta particles with different maximum energies
3.7
mean beta energy
E
mean
fluence averaged energy of the beta particle spectrum at the calibration distance free in air
3.8
parasitic current
Ι
p
negative current produced by beta particles stopped in the collecting portion of the collecting electrode and
diffusing to this electrode and the wire connecting this electrode to the electrometer connector
3.9
phantom
artefact constructed to simulate the scattering properties of the human body or parts of the human body
such as the extremities
Note 1 to entry: A phantom can be used for the definition of a quantity and made of artificial material, e.g. ICRU tissue,
or for the calibration and then be made of physically existing material, see ISO 29661:2012, 6.6.2, for details.
Note 2 to entry: In principle, the ISO water slab phantom, the ISO rod phantom, the ISO water cylinder phantom, or
the ISO pillar phantom should be used, see ISO 29661. For the purposes of this document, however, a polymethyl
methacrylate (PMMA) slab, 20 cm × 20 cm in cross-sectional area by at least 2 cm thickness, is sufficient to simulate
the backscatter properties of the trunk of the human body, while tissue substitutes such as polyethylene terephthalate
(PET) are sufficient to simulate the attenuation properties of human tissue (see 6.2).
[SOURCE: ISO 29661:2012, 3.1.22, modified — Note 2 to entry added.]

ISO 6980-2:2023(en)
3.10
reference point of the extrapolation chamber
point to which the measurement of the distance from the radiation source to the chamber at a given
orientation refers, i.e., the centre of the back surface of the high-voltage electrode of the chamber
3.11
reference absorbed dose
D
R
absorbed dose to tissue, D (0,07), in a slab phantom (3.9) made of ICRU 4-element tissue with an orientation
t
of the phantom (3.9) in which the normal to the phantom (3.9) surface coincides with the (mean) direction of
the incident radiation
[4]
Note 1 to entry: The absorbed dose to tissue, D (0,07), is defined in ICRU 51 as personal absorbed dose, D (0,07). For
t p
the purposes of this document, this definition is extended to a slab phantom.
Note 2 to entry: It is considered that the rear part of the extrapolation chamber approximates a slab phantom with
sufficient accuracy by the material surrounding the standard instrument (extrapolation chamber) used for the
[7][8]
measurement of the beta radiation field .
Note 3 to entry: H (0,07) is obtained by the multiplication of the absorbed dose to tissue at 0,07 mm depth,
p
‑1
D (0,07) = D , with the conversion coefficient 1 Sv Gy , see ISO 6980-3:2023, 5.2.2.2, Formula (3).
t R
3.12
reference beta-particle absorbed dose
D
Rβ
reference absorbed dose, D , (3.11) at a depth of 0,07 mm only due to beta particles
R
Note 1 to entry: As a first approximation, the ratio D /D is given by the correction factor for bremsstrahlung, k ,
Rβ R br
and other photons (see C.3).
3.13
tissue equivalence
property of a material which approximates the radiation attenuation and scattering properties of ICRU tissue
Note 1 to entry: See ISO 6980-1:2023, Annex A; more tissue substitutes are given by ICRU 44.
Note 2 to entry: Further details are given in 6.2.
3.14
transmission function
T (ρ ·d ; α)
m m m
ratio of absorbed dose, D (ρ ·d ; α), in medium m at an area depth, ρ ·d , and angle of radiation incidence,
m m m m m
α, to absorbed dose, D (0; 0°), at the surface of a phantom (3.9)
m
3.15
tissue transmission function,
T (ρ ·d ; α)
t t t
ratio of absorbed dose, D (ρ ·d ;α), in ICRU tissue at an area depth, ρ ·d , and angle of radiation incidence, α,
t t t t t
to absorbed dose, D (0; 0°), at the surface of an ICRU tissue slab phantom (3.9)
t
3.16
zero point
reading of the extrapolation chamber depth indicator which corresponds to a chamber depth of zero, or no
separation of the electrodes
4 Symbols and abbreviated terms and reference and standard test conditions
A list of symbols and abbreviated terms is given in Table 1.

ISO 6980-2:2023(en)
Table 1 — Symbols and abbreviated terms
Symbol Meaning
a effective area of the extrapolation-chamber collecting electrode
BG Bragg-Gray
C external feedback capacitance capacitor
C extrapolation chamber capacitance
k
c sensitivity coefficient
i
d thickness of the absorber in front of the extrapolation chamber
abs
d depth in a medium m
m
d depth in ICRU tissue
t
m
d tissue-equivalent thickness of medium m
t
d reference depth in tissue of 0,07 mm or 3 mm
D (d ) absorbed dose at a depth d in medium m
m m m
D reference absorbed dose
R
D reference beta-particle absorbed dose
Rβ
volume-averaged dose in a detector of thickness v, density ρ at depth d
Dd ,,vr
()
m m
mm
E particle energy (photon energy or electron kinetic energy)
E constant in the saturation correction Formula
E maximum beta energy (kinetic) of a beta-particle spectrum
max
e charge of an electron
f coefficients used for the calculation of k
i pe
H (d) personal dose equivalent at depth d in ICRU tissue
p
H′(d;Ω) directional dose equivalent at depth d, on a radius having direction Ω
I ionization current
I leakage current, not induced by pre-irradiation of the chamber
L
I ionization current caused by bremsstrahlung and other photons
br
I parasitic current
p
I current measured with positive polarity of collecting voltage
+
I current measured with negative polarity of collecting voltage
−
ICRU International Commission on Radiation Units and Measurements
ISO International Organization for Standardization
k product of the extrapolation chamber correction factors which vary during the extrapolation
curve measurement
k′ product of the extrapolation chamber correction factors which are constant during the extrapo‑
lation curve measurement
k correction factor for variations in the attenuation and scattering of beta particles between the
abs
source and the collecting volume and inside the collection volume due to variations from reference
conditions and for differences of the entrance window to a tissue-equivalent thickness of 0,07 mm
k correction factor for the variations of air density in the collecting volume from reference conditions
ad
k correction factor for the difference in backscatter between tissue and the material of the collecting
ba
electrode and guard ring
k correction factor for the effect of bremsstrahlung from the beta-particle source and other photons
br
k correction factor for radioactive decay of the beta particle source
de
k correction factor for electrostatic attraction of the entrance window due to the collecting voltage
el
k
correction factor for the effect of humidity of the air in the collecting volume on W
hu
k correction factor for the inhomogeneity of the absorbed dose rate inside the collecting volume
ih
ISO 6980-2:2023(en)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol Meaning
k correction factor for interface effects between the air of the collecting volume and the adjacent
in
entrance window and collecting electrode
k correction factor for perturbation of the beta-particle flux density by the side walls of the extrap‑
pe
olation chamber
k correction factor for the change of the source to chamber distance once absorbers are placed in
ph
front of the chamber (to increase the phantom depth)
k correction factor for the stopping power ratio of tissue-to-air to use the Spencer-Attix theory
SA
instead of the Bragg-Gray theory
k correction factor for ionization collection losses due to ionic recombination
sat
k correction factor for the change of the stopping power ratio at different phantom depth
Sta

extrapolation chamber depth, the air gap between the collecting electrode and the entrance window
 intercept of the extrapolation curve with the chamber depth axis
m mass of the air in the collecting volume of an extrapolation chamber
a
p ambient atmospheric pressure
PMMA polymethyl methacrylate
PET polyethylene terephthalate
PTFE polytetrafluoroethylene
q measured ionization density
m
(S/ρ) mass-electronic stopping power in medium m
el,m
SA Spencer-Attix
s ratio of mass-electronic stopping powers of ICRU tissue and air
t,a
T ambient air temperature
T parameter for transmission functions
i
T (ρ ·d ; α) transmission function D (ρ ·d ; α)/D (0; 0°) in medium m
m m m m m m m
T (ρ ·d ; α) transmission function D (ρ ·d ; α)/D (0; 0°) in tissue
t t t t t t t
t integration time for a current measurement
t time at which a measurement is performed
m
t reference time to which measurements are corrected to account for radioactive decay
t half-life of a radioisotope
1/2
U absolute value of the collecting voltage in the extrapolation chamber
U , U initial and final voltages on the feedback capacitor charged by current from the extrapolation
1 2
chamber
v thickness of a detector
average energy to produce an ion pair in air under reference conditions
W
x diameter of the geometric collecting electrode area
c
x width of the insulating gap between the collecting and guard electrodes
g
y distance from the source to the reference point of the detector
z distance from the beam axis, perpendicular to that axis
effective atomic number of medium m
Z
m
α angle between the direction of the beam axis and the normal of the surface of the phantom
Γ constant in the saturation-correction-factor Formula
ε dielectric constant for air
a
η beta-particle attenuation scaling factor of medium m relative to medium m
m1,m2 1 2
ρ density of air at ambient conditions
a
ρ density of air at reference conditions
a0
ISO 6980-2:2023(en)
TTabablele 1 1 ((ccoonnttiinnueuedd))
Symbol Meaning
ρ density of medium m
m
ρ density of ICRU tissue
t
σ standard deviation
τ contribution to the dose due to bremsstrahlung and other photons, i.e. τ = 1-k
br br br
Φ spectral distribution of beta-particle fluence
E
The reference conditions as well as the standard test conditions are given in Annex A. All calibrations and
measurements shall be conducted under standard test conditions in accordance with Tables A.1 and A.2.
5 Calibration and traceability of reference radiation fields
The reference absorbed-dose rate of a radiation field established for a calibration in accordance with this
document shall be traceable to a recognized national standard. The method used to provide this calibration
link is achieved through utilization of a transfer standard. This may be a radioactive source or an approved
transfer standard instrument. The calibration of the field is valid in exact terms only at the time of the
calibration, and thereafter shall be inferred, for example, from a knowledge of the half-life and isotopic
composition of the radioactive source.
The measurement technique used by a calibration laboratory for calibrating a beta-particle measuring
device shall also be approved as required by national regulations if available. An instrument of the same,
or similar, type to that routinely calibrated by the calibration laboratory shall be calibrated by both a
reference laboratory recognized by a country’s approval body or institution, if available, and the calibration
laboratory. These measurements shall be performed within each laboratory using its own approved
calibration methods. In order to demonstrate that adequate traceability has been achieved, the calibration
laboratory should obtain the same calibration factor, within agreed-upon limits, as that obtained in the
reference laboratory. The use by the calibration laboratory of standardized sources and holders which have
been calibrated in a national reference laboratory is sufficient to demonstrate traceability to the national
standard.
The frequency of a field calibration should be such that there is reasonable confidence that its value will
not move outside the limits of its specification between successive calibrations. The calibration of the
laboratory-approved transfer instrument, and the check on the measurement techniques used by the
calibration laboratory should be carried out at least every five years, or whenever there are significant
changes in the laboratory environment or as required by national regulations.
6 General principles for calibration of beta‑particle radiation fields
6.1 General
Area and personal doses from beta-particle radiation are often difficult to measure because of their marked
non-uniformity over the skin and variation with depth. In order to correctly measure the absorbed-dose
rate at a point in a phantom in a beta-particle field, a very small detector with very similar absorption and
scattering characteristics as the medium of which the phantom is composed, is needed. Since there is no
ideal detector, recourse shall be made to compromise both in detector size and composition. The concepts of
“scaling factor” and “transmission function” are helpful to account for these compromises.
6.2 Scaling to derive equivalent thicknesses of various materials
[9]
Scaling factors have been developed by Cross to relate the absorbed dose determined in one material to
that in another. These were developed from the observation that, for relatively high-energy beta-particle
sources, dose distributions in different media have the same shape, differing only by a scaling factor, which
Cross denoted as η. Originally observed in the comparison of beta ray attenuation curves in different
media, where η , the scaling factor from medium m to air, was determined from the ratios of measured
m,a
attenuation, the concept has been extended such that, for a plane source of infinite lateral extent, whether

ISO 6980-2:2023(en)
isotropic or a parallel beam, the absorbed dose at an area depth ρ ·d in medium m is related to the
m1 m1 1
absorbed dose, in medium m , at the same area depth ρ ·d , but scaled to η ·ρ ·d , by
2 m2 m2 m1,m2 m2 m2
Dd()ρη⋅ =⋅Ddηρ⋅⋅ =⋅ηηD ⋅ρ ⋅d (1)
() ()
m1 m1 m1 m1,m2m2m1,m2 m2 m2 m1,m2m2m1,m2 mm1 m1
provided that
ρρ⋅=dd⋅ (2)
m1 m1 m2 m2
η is defined as the scaling factor from medium m to medium m . It should be noted that the scaling
m1,m2 1 2
factors are ratios, so that η = 1/η and η = η ·η .
m1,m2 m2,m1 m1,m3 m1,m2 m2,m3
The user should be cautioned that this concept has been demonstrated only for materials of Z or effective
atomic number, Z , less than 18. Values of η calculated for various materials relative to tissue are shown
m m,t
[5]
in Table 2. The data from Table A.2 in ICRU 56 were multiplied by η .
t,w
If m be tissue, and m be a medium m, Formula (1) reduces to
2 1
Ddρη⋅ =⋅Ddηρ⋅⋅ (3)
() ()
mm mm,t tm,t mm
If another depth, d′ in medium m is considered, a similar formula is obtained
m
Ddρη⋅ ''=⋅Ddηρ⋅⋅ (4)
() ()
mm mm,t tm,t mm
The ratio of the absorbed dose at an arbitrary depth to that at the surface (d′ = 0) is defined as the
m
transmission function. Thus, making this substitution and dividing Formula (3) by Formula (4), the following
is obtained
Ddηρ⋅⋅
Ddρ ⋅ ()
()
tm,t mm
mm m
Tdρ ⋅ = = (5)
()
mm m
D ()00D ()
m t
or
Td()ρη⋅ =⋅Tdρ ⋅ (6)
()
mm mt m,tm m
The transmission through a layer of thickness of tissue, η ·ρ ·d , in tissue is equal to the transmission
m,t m m
through a layer of thickness of medium m, ρ ·d , in medium m. Thus the thickness ρ ·d is said to be
m m m m
equivalent to tissue with a thickness of η ·ρ ·d since the transmissions are equal. The equivalent tissue
m,t m m
m
thickness d can be defined as
t
m −1
dd=⋅ηρ ⋅⋅ρ (7)
t m,tm mt
In general, the dose and the transmission functions are functions of both the depth and angle of incidence in
a medium. When they are expressed as above with no angle given, the angle shall be taken as 0°. Materials
with tissue equivalence are listed in ISO 6980-1:2023, Annex A.
6.3 Characterization of the radiation field in terms of penetrability
The tissue transmission function, T (ρ ·d; α), is an important parameter of the reference beta-particle
t t
radiation field. Because of the finite thickness of all detectors used to measure absorbed-dose rate, the
radiation field shall be characterized in terms of penetrability before it can be properly calibrated. Since
the energy fluence of the beta particles in a field changes as the beta particles penetrate the medium, the
determination of the relative dose as a function of depth (or depth-dose function) in a medium shall be
performed with a detector that is not sensitive to this change in energy fluence. For this reason, the relative
depth-dose function shall be determined with a thin (2 mm or less) air ionization chamber. A recommended
method for making this determination with the extrapolation chamber is given in References [10][11]. The

ISO 6980-2:2023(en)
depth-dose functions are then used to construct transmission functions, examples of which are shown
[11][12][13][14]
in Figures 1 and 2 . The measured transmission functions, in conjunction with the calculated
equivalent tissue thicknesses described above, can be used to determine corrections in the measured
absorbed-dose rate to account for depth other than 0,07 mm in a phantom, e.g. 3 mm, and for finite detector
size and non-medium equivalence of the detector material. They can also be used to account for variations in
the absorbed-dose rate at the reference point due to variations in the air density between the source and the
reference point, and for attenuation in non-tissue material in front of the detector, further details are given
as follows (see Clause 7).
For thick detectors, it shall be accounted for the fact that the absorbed-dose rate is averaged over the volume
of a detector. Neglecting any variation in the absorbed dose rate in the plane transverse to the normal
direction of the field, the average absorbed-dose rate of a detector with a thickness v and density ρ, whose
front surface is at a depth d in a phantom of unit density ρ , is given by
t
ρρ⋅+dv⋅ ρρ⋅+dv⋅
t t
D δδ⋅d DT0 ⋅ δ ⋅⋅dδ
() () ()
mm
∫∫
ρ ⋅d ρ ⋅d
t t
Dd(),,v ρ = = =DT()0,⋅ ()dv,ρ (8)
m m
ρ⋅v ρ⋅v
where Td(),,v ρ is the transmission function averaged over the detector volume. For thick detectors
(v > 0,1 mm), this effect may be compensated for by shifting the reference point towards the source.
7 Calibration procedures using an extrapolation chamber
7.1 General
An extrapolation chamber is a primary measurement device for specifying dose rate in beta-particle fields.
It is a parallel plate chamber which consists of components which allow a variable ionization volume to be
[15]
achieved, by movement of one of the plates towards the other. A typical design is shown in Figure 3, which
utilizes a fixed entrance window and a movable collecting electrode. The entrance window also serves as the
high-voltage electrode and consists of a very thin conducting plastic foil. The window shall be thin enough to
not unduly attenuate the beta-particle radiation, yet strong enough to not be deformed by attraction to the
–2
grounded collecting electrode. Carbonized PET foils of about 0,7 mg ⋅ cm are now typical of commercially
available devices. The collecting electrode is maintained at ground potential and defines the cross-sectional
area of the collecting ionization volume. It shall be of conducting material or have a coating of conductive
material, and shall be surrounded by, and electrically insulated from, a guard region. This insulation shall
be thin enough to not perturb the electric field lines in the chamber volume, which ideally are uniform, and
everywhere perpendicular to the two electrodes. In the design shown in Figure 3, the collecting electrode
is constructed from polymethyl methacrylate (PMMA) which has a thin coating of conductive material
in which a narrow groove has been inscribed to define the collecting area. The device shall be equipped
with an accurate means to determine incremental changes in the distance between the two electrodes,
hereafter referred to as the chamber depth; a micrometer attached to the piston which drives the collecting
electrode is usually employed. A bipolar, variable voltage DC power source is used to supply the high voltage
to the entrance window while the collecting electrode is grounded, and a low-noise electrometer is used
to measure the current collected by the collecting electrode. Details of the measurement of the ionization
current are given in Annex B.
7.2 Determination of the reference beta-particle absorbed-dose rate
The absorbed-dose rate to tissue due to beta particles measured with an extrapolation chamber is derived
from the following general relationship:
W
 ΔΙ 

D =⋅s ⋅ (9)
Rtβ ,a
 
e Δm
 
a
BG
where ΔI is the increment of ionization current and Δm is the increment of the mass of air in the collecting
a
volume under Bragg-Gray (BG) conditions. Unfortunately, BG conditions are generally not realized in

ISO 6980-2:2023(en)
measurements of the reference beta-particle radiation fields. To overcome this difficulty, various corrections
are applied and the evaluation of the reference beta-particle absorbed-dose rate is accomplished with
W /es⋅
()
d
0 t,a  

D = {}kk⋅⋅' Ι () (10)
Rβ
 
ρ ⋅a d
 
a0 =0
where
We/ is the quotient of the mean energy required to produce an ion pair in air under
()
reference conditions, see Annex A, and the elementary charge e, with a recom‑
–1[6]
mended value of (33,88 ± 0,12) J⋅C (this value may be used for standard test
conditions without correction);
NOTE This value is obtained by multiplying the recommended value for dry air,
‑1
33,97 J·C , by a humidity correction factor of 0,997 at the relative humidity of 65 %.
ρ is the density of air at the reference conditions of temperature, pressure and
a0
relative humidity, see Annex A;
a is the effective area of the collecting electrode;
d is the limiting value of the slope of the corrected current versus chamber depth
 
′
{}kk⋅ ⋅Ι ()
 
 function;
d 
=0
s is the ratio of the mean mass-electronic stopping powers in tissue-to-air;
t,a
k′ is the product of the correction factors which are independent of the chamber depth;
k is the product of the correction factors which vary with the chamber depth.
The various correction factors are described in Tables 2, 3 and 4, and methods for determining them are
given in Annex C. Methods for determining the limiting slope are given in B.10. The quantity s is given by
t,a
E
max
Φ ⋅ SE/ρ ⋅d
() ()
E
∫ tel,t
s = (11)
t,a
E
max
()Φ ⋅()SE/ρ ⋅d
E
∫ tel,a
where (Φ ) is the spectrum of electrons (fluence of electrons, differential in energy) at the reference point
E t
of the extrapolation chamber, (S/ρ) is the mass-electronic stopping power for an electron with kinetic
el,t
energy E in tissue substitute and (S/ρ) is the corresponding quantity for air. It is assumed that secondary
el,a
electrons (delta rays) deposit their energy where they are generated so that they do not contribute to the
electron fluence. The upper limit of the integrals is given by the maximum beta energy, E , of the beta
max
particles in the fluence spectrum and the lower limit corresponds to the lowest energy in the spectrum, here
indicated by a zero. In principle, this spectrum also includes any electrons set in motion by bremsstrahlung
photons, but these are usually of negligible importance.
[15]
Values for s have been calculated using Formula (11) for several beta-emitting radioisotopes, on the
t,a
idealized assumption that the beta particles continuousl
...