IEC TS 62461:2026

IEC TS 62461 ®
Edition 1.0 2026-07
TECHNICAL
SPECIFICATION
Radiation protection instrumentation - Determination of uncertainty in
measurement
ICS 13.280  ISBN 978-2-8327-1380-8

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CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 List of symbols . 14
5 The ISO/IEC Guide 98-3:2008 and ISO/IEC Guide 98-3-SP1:2008 concept . 16
5.1 General concept of uncertainty determination . 16
5.1.1 Overview . 16
5.1.2 Summary of the analytical method for steps 3 and 4 . 17
5.1.3 Summary of the Monte Carlo method for steps 3 and 4 . 17
5.1.4 Which method to use: Analytical or Monte Carlo? . 18
5.2 Example of a model function . 18
5.3 Collection of data and existing knowledge for the example . 21
5.3.1 General . 21
5.3.2 Calibration factor for the example . 22
5.3.3 Zero reading for the example . 23
5.3.4 Reading for the example . 24
5.3.5 Relative response or correction factor for the example . 25
5.3.6 Comparison of probability density distributions for input quantities . 27
5.4 Calculation of the result of a measurement and its standard uncertainty
(uncertainty budget) . 28
5.4.1 General . 28
5.4.2 Analytical method . 28
5.4.3 Monte Carlo method . 29
5.4.4 Uncertainty budgets . 30
5.5 Statement of the measurement result and its expanded uncertainty . 31
5.5.1 General . 31
5.5.2 Analytical method . 32
5.5.3 Monte Carlo method . 32
5.5.4 Representation of the output distribution function in a simple form
(Monte Carlo method) . 35
6 Decision threshold and detection limit . 35
7 Results below the decision threshold of the measuring device . 37
8 Overview of the annexes . 38
Annex A (informative) Example of an uncertainty analysis for a measurement with an
electronic ambient dose equivalent rate meter according to IEC 60846-1:2009 . 40
A.1 General . 40
A.2 Model function . 40
A.3 Calculation of the complete result of the measurement . 41
A.3.1 General . 41
A.3.2 Low level of consideration of measuring conditions . 42
A.3.3 High level of consideration of measuring conditions . 44
Annex B (informative) Example of an uncertainty analysis for a measurement with a
passive integrating dosimetry system according to IEC 62387:2020 . 47
B.1 General . 47
B.2 Model function . 47
B.3 Calculation of the complete result of the measurement . 48
B.3.1 General . 48
B.3.2 Low level of consideration of exposure conditions . 48
B.3.3 High level of consideration of exposure conditions . 50
B.3.4 Consideration of significant background subtraction . 52
Annex C (informative) Example of an uncertainty analysis for a measurement with an
electronic direct reading neutron ambient dose equivalent rate meter according to
IEC 61005:2014 . 54
C.1 General . 54
C.2 Model function . 54
C.3 Calculation of the complete result of the measurement . 55
C.3.1 General . 55
C.3.2 Analytical method . 55
C.3.3 Monte Carlo method . 57
C.3.4 Comparison of the result of the analytical and the Monte Carlo method . 58
Annex D (informative) Example of an uncertainty analysis for a calibration of a radon
activity monitor according to the IEC 61577 series using a radon gas standard . 60
D.1 General . 60
D.2 Model function . 60
D.3 Calculation of the complete result of the measurement . 61
Annex E (informative) Example of an uncertainty analysis for a measurement of
surface emission rate with a contamination meter according to IEC 60325:2002 . 63
E.1 General . 63
E.2 Model function . 63
E.3 Calculation of the complete result of the measurement . 64
E.3.1 General . 64
E.3.2 Effects of distance . 64
E.3.3 Contamination non-uniformity . 65
E.3.4 Surface absorption . 65
E.3.5 Other input quantities . 65
E.3.6 Uncertainty budget . 66
Annex F (informative) Example of an uncertainty analysis and the determination of the
characteristic limits for a field instrument to measure beta radiation . 69
F.1 General . 69
F.2 Model function . 69
F.3 Calculation of the complete result of the measurement and the decision
threshold and the detection limit . 70
F.3.1 Calibration factor and non-linearity . 70
F.3.2 Correction factor for the energy dependence due to beta radiation
energy . 71
F.3.3 Correction factor for radiation divergence . 73
F.3.4 Further correction factors not considered above . 73
F.3.5 Uncertainty budgets and results. 73
F.3.6 Determination of the characteristic limits (decision threshold, detection
limit and limits of the coverage interval) for a field measurement of beta
radiation . 78
Annex G (informative) Data set to be used for uncertainty estimations for
measurements with radiation detection instruments used for the detection of illicit
trafficking of radioactive materials . 81
G.1 General . 81
G.2 Model functions . 82
G.3 Calculation of the complete result of the measurement . 84
Annex H (informative) Guidance for how to derive an uncertainty budget from the
results of the Monte Carlo . 87
H.1 General description of the method . 87
H.2 R code for the method described in H.1 . 88
Bibliography . 89

Figure 1 – Triangular probability density distribution of values n for the calibration
factor N . 23
Figure 2 – Rectangular probability density distribution of values g for the zero
reading G . 24
Figure 3 – Gaussian probability density distribution of values g for the reading G. 24
Figure 4 – Comparison of different probability density distributions of values:

rectangular (broken line), triangular (dotted line) and Gaussian (solid line) distribution . 27
Figure 5 – Cumulative distribution function Q of the measured value (output quantity)
for the example of low level of consideration of exposure conditions, see 5.3.5.2 . 33
Figure 6 – Probability density distribution (PDF) of the measured value (output
quantity) for the example of low level of consideration of exposure conditions,
see 5.3.5.2. 34
#
Figure 7 – Decision threshold m* and detection limit m . 37
Figure C.1 – Results of the analytical (red dashed lines) and the Monte Carlo method
(grey histogram and blue dotted and solid lines) for Ḣ*(10). 58
Figure D.1 – Result of the analytical (red dashed lines) and the Monte Carlo method
(grey histogram and blue dotted lines) for K . 62
T
Figure F.1 – Energy and angular dependence of the response to H'(0,07) of the survey
meter for beta radiation . 72
Figure F.2 – Results of the analytical (red dashed lines) and the Monte Carlo method
(grey histogram and blue dotted and solid lines) for the measurement of H'(0,07) in an
unknown beta radiation field . 74
Figure F.3 – Results of the analytical (red dashed lines) and the Monte Carlo method
(grey histogram and blue dotted and solid lines) for the measurement of H'(0,07) of a
beta point source and turning the instrument for maximum indication in an unknown
beta radiation field . 77
Figure F.4 – Results of the Monte Carlo method for the determination of uncertainty
(top), the decision threshold (middle) and the detection limit (bottom) for the
measurement of H'(0,07) in an unknown beta radiation field . 79
Figure F.5 – Results of the Monte Carlo method for the determination of uncertainty
(top), the decision threshold (middle) and the detection limit (bottom) for the
measurement of H'(0,07) of a beta point source and turning the instrument for
maximum indication in an unknown beta radiation field . 80

Table 1 – Symbols (and abbreviated terms) used in the main text (excluding annexes) . 14
Table 2 – Standard uncertainty and method to compute the probability density
distributions shown in Figure 4. 28
Table 3 – Example of an uncertainty budget for a measurement with an electronic
dosemeter using the model function M = N K (G – G ) and low level of consideration of
the exposure conditions, see 5.3.5.2 . 31
Table 4 – Example of an uncertainty budget for a measurement with an electronic
dosemeter using the model function M = N K (G – G ) and high level of consideration
of the exposure conditions, see 5.3.5.3 . 31
Table A.1 – Example of an uncertainty budget for a dose rate measurement according
to IEC 60846-1:2009 with an instrument having a logarithmic scale and low level of
consideration of the measuring conditions, see text for details . 43
Table A.2 – Example of an uncertainty budget for a dose rate measurement according
to IEC 60846-1:2009 with an instrument having a logarithmic scale and high level of
consideration of the measuring conditions, see text for details . 45
Table B.1 – Example of an uncertainty budget for a photon dose measurement with a
passive dosimetry system according to IEC 62387:2020 and low level of consideration
of the exposure conditions, see text for details . 49
Table B.2 – Example of an uncertainty budget for a photon dose measurement with a
passive dosimetry system according to IEC 62387:2020 and high level of consideration
of the measuring conditions, see text for details . 51
Table B.3 – Example of an uncertainty budget for a photon dose measurement with a
passive dosimetry system according to IEC 62387:2020 and low level of consideration
of the measuring conditions and significant background subtraction . 53
Table C.1 – Example of an uncertainty budget for a neutron dose measurement
according to IEC 61005:2014 using the analytical method . 56
Table C.2 – Example of an uncertainty budget for a neutron dose rate measurement
according to IEC 61005:2014 using the Monte Carlo method . 57
Table C.3 – Results of the analytical and the Monte Carlo method . 59
Table D.1 – List of quantities used in Formula (D.1) . 60
Table D.2 – List of data available for the input quantities of Formula (D.1) . 61
Table D.3 – Example of an uncertainty budget for the calibration of a radon monitor
according to IEC 61577, see text for details . 61
Table E.1 – Example of an uncertainty budget for a surface emission rate
measurement according to IEC 60325:2002, see text for details . 67
Table E.2 – Example of an uncertainty budget for a surface emission rate
measurement according to IEC 60325:2002 for the determination of the uncertainty at
an assumed true value of zero . 68
Table F.1 – Results of the non-linearity test . 70
Table F.2 – Energy and dose rate dependence for the quantity H'(0.07) . 72
Table F.3 – Uncertainty budget for the measurement of H'(0,07) in an unknown beta
radiation field . 73
Table F.4 – Results of the analytical and Monte Carlo method of the uncertainty
analysis for the measurement of H'(0,07) in an unknown beta radiation field . 74
Table F.5 – Uncertainty budget for the measurement of H'(0,07) of a beta point source
and turning the instrument for maximum indication in an unknown beta radiation field . 76
Table F.6 – Results of the analytical and Monte Carlo method of the uncertainty
analysis for the measurement of H'(0,07) of a beta point source and turning the
instrument for maximum indication in an unknown beta radiation field . 76
Table F.7 – Characteristic limits for the measurement of H'(0,07) in an unknown beta
radiation field . 78
Table F.8 – Characteristic limits for the measurement of H'(0,07) of a beta point source
and turning the instrument for maximum indication in an unknown beta radiation field . 79
Table G.1 – List of standards for the detection of illicit trafficking of radioactive
materials . 81
Table G.2 – Conversion coefficients from exposure rate to ambient dose equivalent
rate for use in Formula (G.4) . 84
Table H.1 – Resulting uncertainty budget from the method described above . 88

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Radiation protection instrumentation -
Determination of uncertainty in measurement

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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shall not be held responsible for identifying any or all such patent rights.
IEC TS 62461, which previously was a Technical Report, has been prepared by
subcommittee 45B: Radiation protection instrumentation, of IEC technical committee 45:
Nuclear instrumentation. It is a Technical Specification.
This first edition of IEC TS 62461 cancels and replaces the second edition of IEC TR 62461
published in 2015. This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) several minor corrections;
b) the addition of an example of the determination of the decision threshold and detection limit
in accordance with ISO 11929.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
45B/1115/DTS 45B/1126/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
INTRODUCTION
ISO/IEC Guide 98-3:2008, Uncertainty of measurement - Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995) as well as its Supplement 1:2008, Propagation of
distributions using a Monte Carlo method (GUM S1), are general guides to assess uncertainty
in measurement. Furthermore, ISO 11929 is a general guide to assess the decision threshold
and detection limit, as well as coverage interval for measurements of ionizing radiation. This
Technical Specification lays emphasis on the application of these documents in the area of
radiation protection and serves as a practical introduction to ISO/IEC Guide 98-3:2008 and its
Supplement 1:2008 as well as ISO 11929.
The process of determining uncertainty delivers not only a numerical value of uncertainty; in
addition, it produces the best estimate of the quantity to be measured, which can differ from the
indication of the instrument. Thus, it can also improve the result of the measurement by using
information beyond the indicated value of the instrument, e.g., the energy dependence of the
instrument. Furthermore, measurement uncertainties and characteristic values, such as the
decision threshold, the detection limit and limits of the coverage interval for measurements, as
well as the best estimate and its associated standard measurement uncertainty, are of
importance in metrology in general and for radiation detection and radiological protection in
particular. The quantification of the uncertainty associated with a measurement result provides
a basis for the trust an individual can have in a measurement result. Conformity with regulatory
limits, constraints or reference values can only be demonstrated by taking into account and
quantifying all sources of uncertainty. Characteristic limits provide the basis for deciding if a
measurement method is suitable and reliable for the proposed measuring task.

1 Scope
This Technical Specification gives guidelines for the application of the uncertainty analysis
according to ISO/IEC Guide 98-3:2008 (GUM describing an analytical method for the
uncertainty determination) and its Supplement 1:2008 (GUM S1 describing a Monte Carlo
method for the uncertainty determination) for measurements of ionizing radiation. It does not
include the uncertainty associated with the concept of the measuring quantity, e.g., the
difference between H (10) on the ISO water slab phantom and on the person.
p
This document explains the principles of ISO/IEC Guide 98-3:2008, its Supplement 1:2008 and
the special considerations necessary for radiation protection at an example taken from
individual dosimetry of external radiation. In the informative annexes, several examples are
given for the application on instruments measuring ionizing radiation, for several of which the
IEC has developed standards.
This document is intended to assist the understanding of ISO/IEC Guide 98-3:2008,
ISO/IEC Guide 98-3-SP1:2008 and other papers on uncertainty analysis. It cannot replace
these papers, nor can it provide the background and justification of the arguments leading to
the concept of ISO/IEC Guide 98-3:2008 and ISO/IEC Guide 98-3-SP1:2008.
Finally, this document gives a very simple method to judge whether a measured result is
significantly different from zero or not based on ISO 11929.
NOTE For a better readability the correct terms are not always used throughout this document. For example, instead
of "random variables of a quantity" only the "quantity" itself is stated.
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.
IEC 60050-311:— , International Electrotechnical Vocabulary (IEV) - Part 311: Electrical and
electronic measurements - General terms relating to measurements
IEC 60050-151, International Electrotechnical Vocabulary (IEV) - Part 151: Electrical and
magnetic devices
ISO/IEC Guide 98-3:2008, Uncertainty of measurement - Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
ISO/IEC Guide 98-3-SP1:2008, Uncertainty of measurement - Part 3: Guide to the expression
of uncertainty in measurement (GUM:1995) - Propagation of distributions using a Monte Carlo
method
ISO 11929-1:2019, Determination of the characteristic limits (decision threshold, detection limit
and limits of the coverage interval) for measurements of ionizing radiation - Fundamentals and
application - Part 1: Elementary applications
ISO 11929-3:2019, Determination of the characteristic limits (decision threshold, detection limit
and limits of the coverage interval) for measurements of ionizing radiation - Fundamentals and
application - Part 3: Applications to unfolding methods
___________
Under consideration. Stage at the time of publication: IEC/CDV 60050-311:2026.
ISO 11929-4:2022, Determination of the characteristic limits (decision threshold, detection limit
and limits of the coverage interval) for measurements of ionizing radiation - Fundamentals and
application - Part 4: Guidelines to applications
3 Terms and definitions
For the purposes of this document, the technical terms of IEC 60050-151, and IEC 60050-311
as well as the following definitions taken from ISO/IEC Guide 98-3:2008, and
ISO/IEC Guide 98-3-SP1:2008 apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
– IEC Electropedia: available at https://www.electropedia.org/
– ISO Online browsing platform: available at https://www.iso.org/obp
3.1
calibration factor
N
quotient of the conventional true value of a quantity, i.e., the conventional quantity value, and
the indicated value for a specified reference radiation under specified reference conditions
3.2
complete result of the measurement
set of values attributed to a measurand, including a value, its uncertainty, coverage interval,
coverage probability, and the unit
Note 1 to entry: The central value of the whole (set of values) can be selected as measured value and a parameter
characterising the dispersion as uncertainty.
Note 2 to entry: The result of a measurement is related to the indication given by the instrument and to the values
of correction obtained by calibration and by the use of a model.
Note 3 to entry: In this Technical Specification, the "measured value", see Note 1, is abbreviated by M.
Note 4 to entry: In this Technical Specification, the "indication given by the instrument", see Note 2, is abbreviated
by G, and called "indicated value".
Note 5 to entry: In this Technical Specification, the "model", see Note 2, is called "model function", see 3.15 and
5.2.
3.3
conformity test
test for conformity evaluation
[SOURCE: IEC 60050-151:2001,151-16-15]
3.4
correction factor
K
factor to the indicated value to correct for deviation of measurement conditions from calibration
conditions
3.5
coverage interval
interval containing the set of true quantity values of a measurand with a stated probability,
based on the information available
Note 1 to entry: A coverage interval does not need to be centred on the chosen measured quantity value.
Note 2 to entry: A coverage interval should not be termed "confidence interval" to avoid confusion with the statistical
concept.
[SOURCE: ISO 11929-1:2019]
3.6
coverage factor
k
cov
numerical factor used as a multiplier of the (combined) standard uncertainty in order to obtain
an expanded uncertainty
Note 1 to entry: A coverage factor k is typically in the range of 2 to 3.
cov
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.6]
3.7
decision threshold
m*
value of the estimator of the measurand, which, when exceeded by the result of an actual
measurement using a given measurement procedure of a measurand quantifying a physical
effect, is used to decide that the physical effect is present
Note 1 to entry: The decision threshold is defined such that in cases where the measurement result, m, exceeds
the decision threshold, m*, the probability of a wrong decision, namely that the true value of the measurand is not
zero if in fact it is zero, is less or equal to a chosen probability, α.
Note 2 to entry: If the result, m, is below the decision threshold, m*, it is decided to conclude that the result cannot
be attributed to the physical effect; nevertheless, it cannot be concluded that it is absent.
Note 3 to entry: In other words: the probability α is the probability that a measured value exceeds the decision
threshold and is accepted as indicator for a non-zero true value although it is, in fact, zero. In this case, the conclusion
m̃ > 0 would be a wrong decision.
[SOURCE: ISO 11929-1:2019, 3.12, modified – addition of Note 3 to entry]
3.8
detection limit
#
m
smallest true value of the measurand which ensures a specified probability of being detectable
by the measurement procedure
Note 1 to entry: With the decision threshold according to 3.7, the detection limit is the smallest true value of the
measurand for which the probability of wrongly deciding that the true value of the measurand is zero is equal to a
specified value, β, when, in fact, the true value of the measurand is not zero. The probability of being detectable is
consequently (1-β).
Note 2 to entry: The terms detection limit and decision threshold are used in an ambiguous way in different
standards (e.g., standards related to chemical analysis or quality assurance). If these terms are referred to one has
to state according to which standard they are used.
Note 3 to entry: In other words: the probability β is the probability that a measured value lies below the decision
#
threshold and the result is therefore not attributed to the physical effect although the true value equals m . In this
case, the conclusion m̃ = 0 would be a wrong decision.
[SOURCE: ISO 11929-1:2019, 3.13, modified – addition of Note 3 to entry]
3.9
deviation
D
difference between the indicated values for the same value of the measurand of an indicating
measuring instrument, or the values of a material measure, when an influence quantity
assumes, successively, two different values
Note 1 to entry: This definition is applicable to all measuring instruments and influence quantities, but it should
mainly be used in those cases, where this deviation is independent of the indicated value.
[SOURCE: IEC 60050-311:2001, 311-07-03, modified – renaming of the term from "variation
(due to an influence quantity)" to "deviation"]
3.10
distribution function
F(x)
function giving, for every value x, the probability that the random variable X be less than or
equal to x: F(x) = Pr(X ≤ x)
[SOURCE: ISO/IEC Guide 98-3:2008, C.2.4; ISO/IEC Guide 98-3:2008-SP1:2008, 3.2]
3.11
evaluator
person performing the measurement and uncertainty analysis
3.12
expanded uncertainty
U
quantity defining an interval about the result of a measurement that may be expected to
encompass a large fraction of the distribution of values that could reasonably be attributed to
the measurand
Note 1 to entry: The expanded uncertainty is obtained by multiplying the (combined) standard uncertainty by a
coverage factor.
[SOURCE: ISO/IEC Guide 98-3:2008, 2.3.5]
3.13
indicated value
G
quantity value provided by a measuring instrument or a measuring system
Note 1 to entry: An indication is often given by the position of a pointer on the display for analogue outputs, a
displayed or printed number for digital outputs, a code pattern for code outputs, or an assigned quantity value for
material measures.
3.14
influence quantity
quantity that is not the measurand but that effects the result of the measurement
Note 1 to entry: For example, temperature of a micrometer used to measure length.
[SOURCE: ISO/IEC Guide 98-3:2008, B.2.10]
3.15
measured value
M
value determined from the indicated value, G, by applying the model function for the meas-
urement
Note 1 to entry: An example of a model function is given below. The calibration factor N, a deviation D, and a
correction factor K are applied:
M = N × K × (G – D)
The calculations according to this model function are not always performed. One main purpose of this model function
of the measurement is, that it is necessary for any determination of the uncertainty according to
ISO/IEC Guide 98-3:2008 (see ISO/IEC Guide 98-3:2008, 3.1.6, 3.4.1 and 4.1; see also 5.2 of this document).
Note 2 to entry: In ISO/IEC Guide 98-3:2008 the "measured value" is called "value of the measurand".
3.16
probability density function
f(x)
derivative (when it exists) of the distribution function:
f(x) = dF(x)/dx
b
Note 1 to entry: f(x) × dx is the "probability element": f(x) × dx = Pr(x = fx( )dx
∫
a
[SOURCE: ISO/IEC Guide 98-3:2008, C.2.5; ISO/IEC Guide 98-3-SP1:2008, 3.3, modified by
adding "in general"]
3.17
reference conditions
set of specified values and/or ranges of values of influence quantities under which the uncer-
tainties, or limits of error, admissible for a measuring instrument are the smallest
[SOURCE: IEC 60050-311:2001, 311-06-02]
3.18
reference response
R
ref
response of the assembly under reference conditions to unit reference dose (rate) or activity
which is expressed as:
G
R =
ref
M
c
where G is the indicated value of the equipment or assembly under test at reference
ref
conditions, G is the zero reading (indicated value without additional radiation) and M is the
0 c,ref
conventional true value of the reference source, i.e., the conventional quantity value
3.19
relative response
R
rel
quotient of the response and the reference response under specified conditions
Note 1 to entry: For the specified reference conditions, the response is the reciprocal of the calibration factor.
3.20
response
R
quotient of the indicated value measured under specified conditions by the equipment or
assembly under test, G, minus the indicated value without additional radiation, G , and the
conventional true value of this quantity, i.e., the conventional quantity value, M :
c
GG−
R=
M
c
3.21
standard uncertainty
standard deviation associated with the measurement result or an input quantity value
Note 1 to entry: See ISO/IEC Guide 98-3:2008, 2.3.4.
Note 2 to entry: The standard uncertainty of the measurement result is sometimes called "combined standard
uncertainty".
Note 3 to entry: The quotient of the standard uncertainty and the measurement result is called "relative standard
uncertainty" and sometimes given as percentage.
3.22
true quantity value
true value of a quantity
true value
quantity value consistent with the defini
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