ISO/FDIS 11929-1

ISO/TC 85/SC 2
Secretariat: AFNOR
Date: 2025-06-19xx
Determination of the characteristic limits (decision threshold,
detection limit and limits of the coverage interval) for measurements
of ionizing radiation — Fundamentals and applications — Part 1:
Elementary applicationsapplication —
Part 1:
Elementary applications
Détermination des limites caractéristiques (seuil de décision, limite de détection et extrémités de l'intervalle
élargi) pour mesurages de rayonnements ionisants — Principes fondamentaux et applications —
Partie 1: Applications élémentaires
FDIS stage
ISO/FDIS 11929-1(E:2025(en)
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© ISO 2025 – All rights reserved
ii
Contents Page
Foreword . v
Introduction . vii
1 Scope . 1
2 Normative references . 2
3 Terms and definitions . 2
4 Quantities and symbols . 6
5 Summary of procedures for evaluating a measurement and calculating the characteristic
limits . 8
5.1 General aspects . 8
5.2 Modelling the measurement . 9
5.3 General considerations about the applicability of the ISO/IEC Guide 98-3 . 9
5.4 Evaluating the input quantities, standard uncertainties and covariances, and the primary
result and its associated standard uncertainty . 10
5.5 Evaluating the standard uncertainty as a function of an assumed true value of the
measurand . 11
5.6 Calculating the decision threshold and decisions to be made . 11
5.7 Calculating the detection limit and assessment of the measurement procedure . 12
5.8 Calculating a coverage interval for the measurand . 13
5.9 Calculating the best estimate of the measurand and its associated standard uncertainty 14
5.10 Reporting the results . 14
6 Fundamentals and evaluation of the measurement . 16
6.1 General aspects concerning the measurand . 16
6.2 Model of evaluation . 16
6.3 Evaluation of the primary measurement result . 18
6.4 Standard uncertainty associated with the primary measurement result . 18
7 Standard uncertainty as a function of an assumed value of the measurand . 19
8 Decision threshold, detection limit and assessments . 21
8.1 Specifications . 21
8.2 Decision threshold . 21
8.3 Detection limit . 22
8.4 Assessments . 23
9 Limits of the coverage interval . 23
9.1 General aspects . 23
9.2 The probabilistically symmetric coverage interval . 24
9.3 The shortest coverage interval . 24
10 The best estimate and its associated standard uncertainty . 25
11 Documentation . 25
Annex A (normative) Repeated counting measurements with random influences . 27
Annex B (normative) Measurements with ratemeters . 32
Annex C (informative) Calculation of the detection limit by iteration . 34
Annex D (informative) Calculations with a generalized net count rate . 36
Annex E (informative) Distribution function of the standardized normal distribution . 39
Bibliography . 44
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ISO/FDIS 11929-1(E:2025(en)
© ISO 2025 – All rights reserved
iv
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
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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 documents 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).
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This document was prepared by ISO/TC 85, Nuclear energy, nuclear technologies, and radiological protection,
Subcommittee SC 2, Radiological protection, in collaboration with the European Committee for
Standardization (CEN) Technical Committee CEN/TC 430, Nuclear energy, nuclear technologies, and
radiological protection, in accordance with the Agreement on technical cooperation between ISO and CEN
(Vienna Agreement).
This third edition cancels and replaces the second edition (ISO 11929-1:2019), of which it constitutes a minor
revision.
The main changes are as follows:
— — correction of the internal references within the text;
— — correction of 0Formulae (3), (A.5), (B.3)
— — 3.12, 0 and 03.13: ;
— correction of the definitions of decision threshold (3.12) and the detection limit (3.13);
— — 5.8: introduction of NOTE 3 in 5.8,, for clarity;
— — 9.1: complement of the NOTE in 9.1;
rst
— — Clause 10: correction of the 1 paragraph and NOTE 2 in 10;
th
— — Annex B: correction of the 8 paragraph in Annex B.
v
ISO/FDIS 11929-1(E:2025(en)
A list of all the parts in the ISO 11929 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.
© ISO 2025 – All rights reserved
vi
Introduction
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 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, at the end, the basis for deciding if uncertainties have to be taken into account.
This standard provides characteristic values of a non-negative measurand of ionizing radiation. It is also
applicable for a wide range of measuring methods extending beyond measurements of ionizing radiation.
The limits to be provided according to ISO 11929 series for specified probabilities of wrong decisions allow
detection possibilities to be assessed for a measurand and for the physical effect quantified by this measurand
as follows:
— — the “decision threshold” allows a decision to be made on whether or not the physical effect quantified
by the measurand is present;
— — the “detection limit” indicates the smallest true quantity value of the measurand that can still be
detected with the applied measurement procedure; this gives a decision on whether or not the
measurement procedure satisfies the requirements and is therefore suitable for the intended
measurement purpose;
— — the “limits of the coverage interval” enclose, in the case of the physical effect recognized as present, a
coverage interval containing the true quantity value of the measurand with a specified probability.
Hereinafter, the limits mentioned are jointly called the “characteristic limits”.
NOTE According to ISO/IEC Guide 99:2007 updated by JCGM 200:2012 the term “coverage interval” is used here
instead of “confidence interval” in order to distinguish the wording of Bayesian terminology from that of conventional
statistics.
All the characteristic values are based on Bayesian statistics and on the ISO/IEC 98-3 as well as on the ISO/IEC
Guide 98-3:2008/Suppl 1:2008 and ISO/IEC Guide 98-3:2008/Suppl 2:2011. As explained in detail in
ISO 11929-2, the characteristic values are mathematically defined by means of moments and quantiles of
probability distributions of the possible measurand values.
Since measurement uncertainty plays an important part in ISO 11929, the evaluation of measurements and
the treatment of measurement uncertainties are carried out by means of the general procedures according to
the ISO/IEC Guide 98-3 and to the ISO/IEC Guide 98-3:2008/Suppl 1:2008; see also References [0[13]] to
[0[17].]. This enables the strict separation of the evaluation of the measurements, on the one hand, and the
provision and calculation of the characteristic values, on the other hand. The ISO 11929 series makes use of a
[ [18]] [ [20]]
theory of uncertainty in measurement 0 to 0 based on Bayesian statistics (e.g. see References [0[21]] to
[0[26])]) in order to take into account those uncertainties that cannot be derived from repeated or counting
measurements. The latter uncertainties cannot be handled by frequentist statistics.
Because of developments in metrology concerning measurement uncertainty laid down in the ISO/IEC G
...