prEN ISO 13164-2

• Abstract:

  ISO 13164-2:2013 specifies a test method for the determination of radon-222 activity concentration in a sample of water following the measurement of its short-lived decay products by direct gamma-spectrometry of the water sample.; The radon-222 activity concentrations, which can be measured by this test method utilizing currently available gamma-ray instruments, range from a few becquerels per litre to several hundred thousand becquerels per litre for a 1 l test sample.; This test method can be used successfully with drinking water samples. The laboratory is responsible for ensuring the validity of this test method for water samples of untested matrices.; An annex gives indications on the necessary counting conditions to meet the required sensitivity for drinking water monitoring.

• Status: Not Published
• Publication Date: 02-Nov-2027
• ICS: 13.060.60 - Examination of physical properties of water
• ICS: 13.280 - Radiation protection
• ICS: 17.240 - Radiation measurements
• Technical Committee: CEN/TC 230 - Water analysis
• Current Stage: 4060 - Closure of enquiry - Enquiry
• Start Date: 06-Aug-2026
• Completion Date: 06-Aug-2026
• Ref Project: oSIST prEN ISO 13164-2:2026 - Water quality - Radon-222 - Part 2: Test method using gamma-ray spectrometry (ISO/DIS 13164-2:2026)

• Revises: EN ISO 13164-2:2020 - Water quality - Radon-222 - Part 2: Test method using gamma-ray spectrometry (ISO 13164-2:2013)
• Effective Date: 05-Nov-2024

prEN ISO 13164-2 is a CEN water-quality standard for determining radon-222 (Rn) activity concentration in water by direct gamma-ray spectrometry of the sample. It is written for laboratories that measure drinking water and other water samples and need results with uncertainty, decision threshold, and detection limit information. The method uses the gamma emissions from the short-lived decay products of Rn and is described for a 1 l test sample over a wide activity-concentration range.

What does prEN ISO 13164-2 specify?

prEN ISO 13164-2 specifies a test method for measuring Rn activity concentration in water by gamma-ray spectrometry of the water sample itself. The standard says the method can be used for drinking water and that the laboratory is responsible for confirming validity for untested water matrices.

The document is organized into clauses on scope, references, terms, symbols, principle, sampling, transport and storage, detection, measurement procedure, quality assurance and quality control, expression of results, calibration, and test report. It also includes two informative annexes.

Annex	What it covers
Annex A	Sample spectra, shown for thallium-doped sodium iodide [NaI(Tl)] and high-purity germanium [HPGe] detectors
Annex B	Sample accuracy and precision data, including example characteristic limits for different detector setups

What are the key requirements of prEN ISO 13164-2?

Sampling and sample handling

Clause 6 requires a representative sample of the water at the time of sampling. The sample is to be taken in line with ISO 5667-1, ISO 5667-3, and ISO 13164-1, and transferred directly into the measurement container so that air is excluded and radon degassing is avoided.

In practice, that means the sampling container matters as much as the sample itself. The container and cap are to be inert, have low gamma attenuation, and not adsorb or let radon or its short-lived decay products permeate through them. A sample volume of at least 1 l is recommended, and the water temperature is to be measured during sampling.

Transport, storage, and timing

Clause 7 requires the sample to be kept colder than the original water, but above 0 °C, until analysis. The container is to be tightly sealed, protected against leakage, and the delay before analysis kept as short as possible.

The standard also says analysis should begin after radioactive equilibrium has been reached, and the time between sampling and analysis is not to exceed 48 h. In practice, this is important because radon decays quickly and can be lost from a poorly handled sample, which would bias the result low.

Detection, calibration, and measurement procedure

Clause 8 states that the activity concentration is determined from gamma emissions from bismuth (Bi) and/or lead (Pb) progeny measured by direct gamma-spectrometry. High-resolution gamma-ray spectrometry is preferred, and the equipment selection is to follow IEC 60973 and IEC 61151.

The measurement is to start at least 3 h after sampling, once Rn and its short-lived decay products are in radioactive equilibrium. Calibration is to follow IEC 61452, using for example a radium (Ra) calibration source in secular equilibrium with the short-lived decay product being measured. The standard also gives a practical warning for software decay correction: when the progeny half-life is much shorter than the parent half-life, the parent half-life is to be used for the decay correction in the software.

Quality assurance, uncertainty, and reporting

Clause 10 requires the quality control programme to meet ISO/IEC 17025. The laboratory is to correct for radon decay between sampling and measurement and to control influence quantities such as water temperature, turbulence, head-space air, atmospheric radon near the detector, Ra in the water, and suspended material.

Instrument verification, method verification, and analyst capability checks are all part of the routine control system. The standard calls for periodic checks of energy calibration, efficiency calibration, and background spectrum, plus accuracy checks using intercomparison exercises or reference materials, and duplicate testing for analyst capability.

Clause 11 then gives the calculation framework for the activity concentration, standard uncertainty, decision threshold, limit of detection, and coverage intervals. That is what turns a measured spectrum into a reportable result with uncertainty. Clause 13 completes the process by defining the minimum report content, including the standard reference, sample identification, units, result, radionuclide reference, calculation date, report date, and relevant sampling and analysis dates when they affect validity.

What terms does prEN ISO 13164-2 define?

• Activity concentration - The amount of Rn per litre of water, expressed at the date and time of sampling.
• Standard uncertainty - The uncertainty associated with the measured activity concentration before applying a coverage factor.
• Expanded uncertainty - The uncertainty reported with the result after multiplying the standard uncertainty by a coverage factor, with the standard using k = 2.
• Decision threshold - The result level used, under ISO 11929, to decide whether the measured activity is considered detected.
• Limit of detection - The lowest activity concentration that can be distinguished from background with the probability criteria used in ISO 11929.
• Coverage interval - The interval around the measured activity concentration used to express confidence in the result, either as a probabilistically symmetric interval or as the shortest interval.
• Secular equilibrium - The condition required for a calibration source when the short-lived decay product being measured has reached a stable activity relationship with its parent.
• Calibration factor - The factor used in the calculation chain for the gamma-spectrometry result.

Who uses prEN ISO 13164-2?

prEN ISO 13164-2 is used by testing laboratories that measure radioactivity in water, especially laboratories working on drinking water monitoring, environmental radioactivity, and compliance testing. It is also relevant to quality managers and technical staff who set up sampling, gamma spectrometry, calibration, and reporting procedures.

Water utilities, public-health laboratories, regulators, and contract testing laboratories use the document when they need comparable results for radon in water. The method is especially useful when the reported value must be accompanied by uncertainty, decision threshold, or detection limit information for compliance or screening decisions.

What changed in prEN ISO 13164-2 from the previous edition?

The second edition cancels and replaces ISO 13164-2:2013 and states that it has been technically revised. The foreword lists these main changes:

• a common Introduction template was implemented for the ISO 13164 series parts under revision
• edits were made to improve consistency with the other ISO 13164 parts
• the Symbols clause was updated
• the decay correction calculations were clarified
• the annexes and bibliography were updated
• additional clarifying edits were made

Which standards are used with prEN ISO 13164-2?

Standard	Contribution to prEN ISO 13164-2
ISO 5667-1	Guidance for sampling programme design and sampling techniques
ISO 5667-3	Requirements for preservation and handling of water samples
ISO 10703	High-resolution gamma-ray spectrometry method for gamma-emitting radionuclides
ISO 11929 (all parts)	Decision threshold, detection limit, and confidence/coverage interval calculations
ISO 13164-1	General principles for the radon-222 series
ISO/IEC 17025	Laboratory competence and quality control framework
ISO 80000-10	Quantities, units, and symbols for atomic and nuclear physics
IEC 60973	Test procedures for germanium gamma-ray detectors
IEC 61151	Test procedures for amplifiers and preamplifiers used with ionizing-radiation detectors
IEC 61452	Calibration and use of germanium spectrometers
IEC 61577-1	General principles for radon and radon decay product measuring instruments
IEC 61577-2	Specific requirements for radon measuring instruments

What does the prEN ISO 13164-2 document contain?

Clause 5 explains the measurement principle and links the result to gamma emissions from the short-lived decay products of Rn. Table 1 gives the main gamma-ray energies and emission probabilities used by the method.

Clause 11 contains the calculation framework for the activity concentration, uncertainty, decision threshold, limit of detection, and coverage intervals. Annex A shows example spectra from NaI(Tl) and HPGe detectors, and Annex B gives example characteristic limits for different detector setups, sample volumes, and counting times.

SLOVENSKI STANDARD
01-september-2026
Kakovost vode - Radon Rn-222 - 2. del: Preskusna metoda z gama spektrometrijo
(ISO/DIS 13164-2:2026)
Water quality - Radon-222 - Part 2: Test method using gamma-ray spectrometry
(ISO/DIS 13164-2:2026)
Wasserbeschaffenheit - Radon-222 - Teil 2: Verfahren mittels Gammaspektrometrie
(ISO/DIS 13164-2:2026)
Qualité de l'eau - Radon 222 - Partie 2: Méthode d'essai par spectrométrie gamma
(ISO/DIS 13164-2:2026)
Ta slovenski standard je istoveten z: prEN ISO 13164-2
ICS:
13.060.60 Preiskava fizikalnih lastnosti Examination of physical
vode properties of water
17.240 Merjenje sevanja Radiation measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 13164-2
ISO/TC 147/SC 3
Water quality — Radon-222 —
Secretariat: AFNOR
Part 2:
Voting begins on:
Test method using gamma-ray 2026-04-10
spectrometry
Voting terminates on:
2026-07-03
Qualité de l'eau — Radon 222 —
Partie 2: Méthode d'essai par spectrométrie gamma
ICS: 13.060.60; 13.280; 17.240
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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Reference number
ISO/DIS 13164-2:2026(en)
DRAFT
ISO/DIS 13164-2:2026(en)
International
Standard
ISO/DIS 13164-2
ISO/TC 147/SC 3
Water quality — Radon-222 —
Secretariat: AFNOR
Part 2:
Voting begins on:
Test method using gamma-ray
2026-04-10
spectrometry
Voting terminates on:
2026-07-03
Qualité de l'eau — Radon 222 —
Partie 2: Méthode d'essai par spectrométrie gamma
ICS: 13.060.60; 13.280; 17.240
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland Reference number
ISO/DIS 13164-2:2026(en)
ii
ISO/DIS 13164-2:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Symbols . 2
5 Principle . 3
6 Sampling . 4
6.1 General requirement .4
6.2 Sampling requirement .4
6.3 Sample volume .4
6.4 Container characteristics .4
7 Transportation and storage . 4
8 Detection . 5
9 Measurement procedure . 5
10 Quality assurance and quality control programme . 5
10.1 General .5
10.2 Influence quantities .5
10.3 Instrument verification .6
10.4 Method verification .6
10.5 Demonstration of analyst capability . .7
11 Expression of results . 7
11.1 Activity concentration .7
11.2 Standard uncertainty of the activity concentration .7
11.3 Decision threshold .8
11.4 Limit of detection .8
11.5 Limits of the coverage intervals .9
11.5.1 Limits of the probabilistically symmetric coverage interval .9
11.5.2 The shortest coverage interval .9
12 Calibration . 9
13 Test report . 10
Annex A (informative) Sample spectra .11
Annex B (informative) Sample accuracy and precision data .13
Bibliography . 14

iii
ISO/DIS 13164-2:2026(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 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).
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 147, Water Quality, Subcommittee SC 3,
Radioactivity measurements.
This second edition cancels and replaces the first edition (ISO 13164-2:2013), which has been technically
revised.
The main changes are as follows:
— A common Introduction template for the ISO 13164 series parts under revision was implemented
— Edits to improve consistency with content of other ISO 13164 parts
— Updates to Symbols clause content
— Clarified decay correction calculations
— Annex and Bibliography updates
— Additional clarifying edits.
A list of all parts in the ISO 13164 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.

iv
ISO/DIS 13164-2:2026(en)
Introduction
Radionuclides are present throughout the environment; thus, water bodies (e.g. surface waters, ground
waters, sea waters) contain radionuclides, which can be of either natural or anthropogenic origin:
3 14 40
— naturally occurring radionuclides, including H, C, K and those originating from the thorium and
210 210 222 226 228 227 232 231 234 238
uranium decay series, in particular Pb, Po, Rn, Ra, Ra, Ac, Th, Pa, U, and U
can be found in water bodies due to either natural processes (e.g., desorption from the soil, runoff by rain
water) or released from technological processes involving naturally occurring radioactive materials (e.g.
mining, mineral processing, oil, gas and production, water treatment and the production and the use of
phosphate fertilisers);
55 59 63 90 99
— anthropogenic radionuclides such as Fe, Ni, Ni, Sr, Tc, transuranic elements (Np, Pu, Am,
60 137
and Cm)and some gamma emitting radionuclides such as Co and Cs can also be found in natural
waters. Small quantities of anthropogenic radionuclides can be discharged from nuclear facilities to the
environment as a result of authorized routine releases. The radionuclides present in liquid effluents
[1]
are usually controlled before being discharged to the environment and water bodies. Anthropogenic
radionuclides used in medical and industrial applications can be released to the environment after use.
Anthropogenic radionuclides are also found in waters due to the contamination from fallout resulting
above-ground nuclear detonations and accidents such as those that occurred at the Chornobyl and
Fukushima nuclear facilities.
Radionuclide activity concentrations in water bodies can vary according to local geological characteristics
and climatic conditions and can be locally and temporally enhanced by releases from nuclear facilities
[2][3]
during planned, existing, and emergency exposure situations . Some drinking water sources can thus
contain radionuclides at activity concentrations that could present a human health risk. The World Health
[4]
Organization (WHO) recommends to routinely monitor radioactivity in drinking waters and to take
proper actions when needed to minimize the health risk.
National regulations usually specify the activity concentration limits that are authorized in drinking waters,
water bodies, and liquid effluents to be discharged to the environment. These limits can vary for planned,
existing, and emergency exposure situations. The WHO does not have a current recommended specific
activity concentration limit for radon in water as radon exposure through indoor air is considered a more
[4]
pressing concern, while in Europe, the implementation of European Council Directive 2013/51/EURATOM,
-1
establishes a radon concentration limit of 100 Bq·l . Compliance with such limits is assessed by measuring
radioactivity in water samples and by comparing the results obtained with their associated uncertainties as
[5] [6]
specified by ISO/IEC Guide 98-3 and ISO 5667-20 .
This document contains method to support laboratories which need to determine Rn in water samples.
The method described in this document can be used for various types of waters (see Clause 1). Minor
modifications such as sample volume and counting time can be made if needed to ensure that the
characteristic limit, decision threshold, detection limit, and uncertainties are below the required limits.
This can be done for several reasons such as emergency situations, lower national guidance limits, and
operational requirements.
v
DRAFT International Standard ISO/DIS 13164-2:2026(en)
Water quality — Radon-222 —
Part 2:
Test method using gamma-ray spectrometry
WARNING — Persons using this document should be familiar with normal laboratory practices. This
document does not purport to address all of the safety problems, if any, associated with its use. It is
the responsibility of the user to establish appropriate safety and health practices and to determine
the applicability of any other restrictions.
IMPORTANT — It is absolutely essential that tests conducted in accordance with this document be
carried out by suitably qualified staff.
1 Scope
This part of ISO 13164 specifies a test method for the determination of Rn activity concentration in a
sample of water by the measurement of its short-lived decay products by direct gamma-spectrometry of a
water sample (see Annex A).
The Rn activity concentrations, which can be measured by this test method utilizing currently available
gamma-ray instruments, range from a few becquerels per litre to several hundred thousand becquerels per
litre for a 1 l test sample.
This test method can be used successfully with drinking water samples. The laboratory is responsible for
ensuring the validity of this test method for water samples of untested matrices.
Annex B gives indication on the necessary counting conditions to meet the required sensitivity for drinking
water monitoring.
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 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and sampling
techniques
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 10703, Water quality — Gamma-ray emitting radionuclides — Test method using high resolution gamma-
ray spectrometry
ISO 11929 (all parts), Determination of the characteristic limits (decision threshold, detection limit and limits of
the confidence interval) for measurements of ionizing radiation — Fundamentals and application
ISO 13164-1, Water quality — Radon-222 — Part 1: General principles
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
ISO 80000-10, Quantities and units — Part 10: Atomic and nuclear physics
IEC 60973, Test procedures for germanium gamma-ray detectors

ISO/DIS 13164-2:2026(en)
IEC 61151, Nuclear instrumentation — Amplifiers and preamplifiers used with detectors of ionizing radiation —
Test procedures
IEC 61452, Nuclear instrumentation — Measurement of gamma-ray emission rates of radionuclides —
Calibration and use of germanium spectrometers
IEC 61577-1, Radiation protection instrumentation — Radon and radon decay product measuring instruments
— Part 1: General principles
IEC 61577-2, Radiation protection instrumentation — Radon and radon decay product measuring instruments
— Part 2: Specific requirements for radon measuring instruments
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 80000-10 and ISO 13164-1 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/
4 Symbols
For the purposes of this document, the symbols defined in ISO 80000-10, ISO 13164-1, and the following
apply.
A activity of each radionuclide in calibration source, at the Bq
calibration time
222 −1
c activity concentration of Rn in water Bq·l
A
−1
*
Bq·l
decision threshold
c
A
−1
# Bq·l
limit of detection
c
A
−1
 
Bq·l
lower and upper limits of the probabilistically symmetric coverage interval
c , c
A A
−1

Bq·l
lower and upper limits of the shortest coverage interval
cc,
AA
f correction factor for the decay of radon during time
...