Water quality — Radium-226 — Part 1: Test method using liquid scintillation counting

This document specifies the determination of radium-226 (226Ra) activity concentration in non-saline water samples by extraction of its daughter radon-222 (222Rn) and its measurement using liquid scintillation analysis. The test method described in this document, using currently available scintillation counters, has a detection limit of approximately 50 mBq·l−1. This method is not applicable to the measurement of other radium isotopes.

Qualité de l'eau — Radium-226 — Partie 1: Méthode d'essai par comptage des scintillations en milieu liquide

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Published
Publication Date
14-Nov-2022
Current Stage
6060 - International Standard published
Due Date
13-Jun-2021
Completion Date
15-Nov-2022
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INTERNATIONAL ISO
STANDARD 13165-1
Second edition
2022-11
Water quality — Radium-226 —
Part 1:
Test method using liquid scintillation
counting
Qualité de l'eau — Radium-226 —
Partie 1: Méthode d'essai par comptage des scintillations en milieu
liquide
Reference number
ISO 13165-1:2022(E)
© ISO 2022
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ISO 13165-1:2022(E)
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© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

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© ISO 2022 – All rights reserved
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ISO 13165-1:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction .................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

4 Symbols and units............................................................................................................................................................................................... 2

5 Principle ........................................................................................................................................................................................................................ 2

6 Reagents and equipment ............................................................................................................................................................................. 3

6.1 Reagents ....................................................................................................................................................................................................... 3

6.2 Equipment ................................................................................................................................................................................................... 3

7 Sampling ....................................................................................................................................................................................................................... 4

8 Instrument set-up and calibration.................................................................................................................................................... 4

8.1 Preparation of calibration sources ....................................................................................................................................... 4

8.2 Optimization of counting conditions .................................................................................................................................. 4

8.3 Detection efficiency ........................................................................................................................................................................... 4

8.4 Blank sample preparation and measurement............................................................................................................. 5

9 Procedure ....................................................................................................................................................................................................................5

9.1 Direct counting ....................................................................................................................................................................................... 5

9.2 Thermal preconcentration ........................................................................................................................................................... 5

9.3 Sample preparation ............................................................................................................................................................................ 6

9.4 Sample measurement ....................................................................................................................................................................... 6

10 Quality control ....................................................................................................................................................................................................... 6

11 Expression of results ....................................................................................................................................................................................... 7

11.1 Calculation of massic activity ........................................................................................................................................... ......... 7

11.2 Standard uncertainty ....................................................................................................................................................................... 7

11.3 Decision threshold .............................................................................................................................................................................. 8

11.4 Detection limit ........................................................................................................................................................................................ 8

11.5 Limits of the coverage intervals .............................................................................................................................................. 8

11.5.1 Limits of the probabilistically symmetric coverage interval ..................................................... 8

11.5.2 Shortest coverage interval ........................................................................................................................................ 9

11.6 Calculations using the activity concentration ............................................................................................................ 9

12 Interference control .........................................................................................................................................................................................9

13 Test report .................................................................................................................................................................................................................. 9

[13]

Annex A (informative) Set-up parameters and validation data ..................................................................................11

Bibliography .............................................................................................................................................................................................................................15

iii
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ISO 13165-1:2022(E)
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).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

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 13165-1:2013), which has been technically

revised.
The main changes are as follows:
— the introduction has been updated;
— the list of symbols has been updated;
— the expression of results has been updated;
— the test report has been updated;
— the validation data has been updated;
A list of all parts in the ISO 13165 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 2022 – All rights reserved
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ISO 13165-1:2022(E)
Introduction

Radioactivity from several naturally-occurring and anthropogenic sources is present throughout the

environment. Thus, water bodies (such as surface waters, ground waters, sea waters) can contain

radionuclides of natural, human-made, or both origins.
40 3 14

— Natural radionuclides, including K, H, C, and those originating from the thorium and uranium

226 228 234 238 210 210
decay series, in particular Ra, Ra, U, U, Po and Pb can be found in water for

natural reasons (e.g. desorption from the soil and washoff by rain water) or can be released from

technological processes involving naturally occurring radioactive materials (e.g. the mining and

processing of mineral sands or phosphate fertilizers production and use).

— Anthropogenic radionuclides such as transuranium elements (americium, plutonium, neptunium,

3 14 90

curium), H, C, Sr and gamma emitting radionuclides can also be found in natural waters.

Small quantities of these radionuclides are discharged from nuclear fuel cycle facilities into the

environment as a result of authorized routine releases. Some of these radionuclides used for

medical and industrial applications are also released into the environment after use. Anthropogenic

radionuclides are also found in waters as a result of past fallout contaminations resulting from

the explosion in the atmosphere of nuclear devices and accidents such as those that occurred in

Chernobyl and Fukushima.

Radionuclide activity concentration in water bodies can vary according to local geological

characteristics and climatic conditions and can be locally and temporally enhanced by releases from

[1]

nuclear installations during planned, existing and emergency exposure situations. Drinking water

can thus contain radionuclides at activity concentrations which can present a risk to human health.

The radionuclides present in liquid effluents are usually controlled before being discharged into the

[2]

environment and water bodies. Drinking waters are monitored for their radioactivity content as

[3]

recommended by the World Health Organization (WHO) so that proper actions can be taken to ensure

that there is no adverse health effect to the public. Following these international recommendations,

national regulations usually specify radionuclide authorized concentration limits for liquid effluent

discharged to the environment and radionuclide guidance levels for waterbodies and drinking waters

for planned, existing and emergency exposure situations. Compliance with these limits can be assessed

using measurement results with their associated uncertainties as specified by ISO/IEC Guide 98-3 and

[4]
ISO 5667-20 .

Depending on the exposure situation, there are different limits and guidance levels that would result in

an action to reduce health risk. As an example, during planned or existing situation, the WHO guidelines

−1 226
for guidance level in drinking water is 1 Bq·l for Ra activity concentration.

NOTE 1 The guidance level (GL) is the activity concentration with an intake of 2 l·d of drinking water for

one year that results in an effective dose of 0,1 mSv·a for members of the public. This is an effective dose

that represents a very low level of risk and which is not expected to give rise to any detectable adverse health

[7]
effects .
[5]

In the event of a nuclear emergency, the WHO Codex Guideline Levels mentioned that the activity

concentration can be greater.

NOTE 2 The Codex GLs apply to radionuclides contained in foods destined for human consumption and traded

internationally, which have been contaminated following a nuclear or radiological emergency. These GLs apply to

food after reconstitution or as prepared for consumption, i.e. not to dried or concentrated foods and are based on

[5]

an intervention exemption level of 1 mSv in a year for members of the public (infant and adult) .

Thus, the test method can be adapted so that the characteristic limits, decision threshold, detection

limit and uncertainties ensure that the radionuclide activity concentrations test results can be verified

to be below the guidance levels required by a national authority for either planned/existing situations

[6][7]
or for an emergency situation .

Usually, the test methods can be adjusted to measure the activity concentration of the radionuclide(s)

in either wastewaters before storage or in liquid effluents before being discharged to the environment.

© ISO 2022 – All rights reserved
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ISO 13165-1:2022(E)

The test results will enable the plant/installation operator to verify that, before their discharge,

wastewaters/liquid effluent radioactive activity concentrations do not exceed authorized limits.

The test method(s) described in this document may be used during planned, existing and emergency

exposure situations as well as for wastewaters and liquid effluents with specific modifications that can

increase the overall uncertainty, detection limit and threshold.

The test method(s) may be used for water samples after proper sampling, sample handling and test

sample preparation (see the relevant part of the ISO 5667 series).

This document has been developed to answer the need of test laboratories carrying out these

measurements, that are sometimes required by national authorities, as they can be required to obtain a

specific accreditation for radionuclide measurement in drinking water samples.

This document is one of a set of International Standards on test methods dealing with the measurement

of the activity concentration of radionuclides in water samples.
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INTERNATIONAL STANDARD ISO 13165-1:2022(E)
Water quality — Radium-226 —
Part 1:
Test method using liquid scintillation counting

WARNING — Persons using this document should be familiar with normal laboratory practice.

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 according to this document be

carried out by suitably trained staff.
1 Scope
226

This document specifies the determination of radium-226 ( Ra) activity concentration in non-saline

222

water samples by extraction of its daughter radon-222 ( Rn) and its measurement using liquid

scintillation analysis.

The test method described in this document, using currently available scintillation counters, has a

detection limit of approximately 50 mBq·l . This method is not applicable to the measurement of other

radium isotopes.
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 3696, Water for analytical laboratory use — Specification and test methods

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/IEC 17025, General requirements for the competence of testing and calibration laboratories

ISO 80000-10, Quantities and units — Part 10: Atomic and nuclear physics

ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in

me a s ur ement (GUM: 1995)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 80000-10, ISO/IEC Guide 98-3

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/
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ISO 13165-1:2022(E)
4 Symbols and units

For the purposes of this document, the symbols given in Table 1, ISO 80000-10 and ISO/IEC Guide 98-3

apply.
Table 1 — Symbols
Symbol Description Unit
a Massic activity of the sample at the measuring time Bq·g
226 −1
a Massic activity of the Ra standard solution at the measuring time Bq·g
a* Decision threshold for the massic alpha-activity Bq·g
# −1
a Detection limit for the massic alpha-activity Bq·g
⊲ ⊳ −1

a , a Lower and upper limits of the probabilistically symmetric coverage interval Bq·g

< > −1
a , a Lower and upper limits of the shortest coverage interval Bq·g
c Concentration mol· l
c Activity concentration Bq·l
k Coverage factor —
m Mass of the test sample g
m Mass of initial sample subject to heating or possibly concentration g
m Mass of heated or concentrated sample g
m Mass of heated or concentrated sample transferred in the vial g
226

m Mass of Ra standard solution used for the preparation of the calibration sample g

p Probability (for instance p = 1 − α , 1− β or 1- γ /2) —
q Probability —
r Blank sample count rate in the alpha-window s
r Sample gross count rate in the alpha-window s
r Count rate of the calibration sample in the alpha-window s
t Blank sample counting time s
t Sample counting time s
t Calibration sample counting time s
u(a) Standard uncertainty associated with the measurement result Bq·l
ũ(ã) Standard uncertainty of a as a function of its true value —
u Relative standard uncertainty —
rel
u Combined uncertainty —
U Expanded uncertainty, calculated using U = ku(a), with k = 1, 2, … Bq·l
w Factor equal to 1/ε m —
ε Alpha-efficiency, relative —
ρ Density g·l
Φ Distribution function of the standardized normal distribution —
ω Auxiliary quantity —
γ Coverage interval probability —
5 Principle
226 222

The massic activity of Ra is indirectly determined by isolating its progeny Rn by liquid scintillation

222 226 222

counting (LSC). Rn is in secular equilibrium with its parent, Ra, after 30 d (99,56 %). Rn is

extracted from the aqueous solution using a scintillation cocktail, within the scintillation vial, that is

immiscible in water (see References [8], [9], [10] and [11]).
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ISO 13165-1:2022(E)

The aqueous sample is acidified, heated and, if possible, concentrated by slow evaporation in order to

222

desorb Rn and to achieve a better detection limit. The concentrated aqueous sample is transferred

into a radon-tight scintillation vial and a water-immiscible scintillation cocktail is added.

After 30 d, the sample is measured by liquid scintillation counting (LSC) applying alpha and beta

222 218 214

discrimination; only alpha-emission of Rn and that of its short-lived progenies ( Po and Po) are

considered, as this counting condition ensures a better detection limit.
6 Reagents and equipment
6.1 Reagents

All reagents shall be of recognized analytical grade and, except for 6.1.4, shall not contain any detectable

alpha- and beta-activity.

6.1.1 Laboratory water, distilled or deionized, conforming with ISO 3696, grade 3.

222

Deionized water can contain detectable amounts of Rn and short-lived progeny. It is therefore

strongly recommended that water be boiled under vigorous stirring and allowed to stand for 1 d before

use. Otherwise, purge it with nitrogen for about 1 h for 2 l.
−1 −1

6.1.2 Nitric acid, c(HNO ) = 15,8 mol· l , ρ = 1,42 g ml , mass fraction w(HNO ) = 70 %.

3 3

6.1.3 Scintillation cocktail, commercially available scintillation cocktails, water immiscible and

suitable for alpha and beta discrimination (e.g. diisopropylnaphthalene-based cocktails).

226
6.1.4 Ra standard solution
226

Ra standard solutions shall be provided with calibration certificates containing at least the

activity concentration, measurement uncertainty and/or statement of compliance with an identified

metrological specification.
6.2 Equipment
6.2.1 Balance.
6.2.2 Hotplate with magnetic stirrer and stirring bar.
6.2.3 pH-meter.

6.2.4 Wide-mouth high density polyethylene (HDPE) sample bottles, volumes between 100 ml

and 500 ml.

6.2.5 Liquid scintillation counter, with alpha and beta discrimination option, with thermostated

counting chamber and preferably an ultra-low level counter to achieve better detection limits.

6.2.6 Polyethylene scintillation vials, polytetrafluoroethylene (PTFE) coated, 20 ml.

PTFE-coated polyethylene vials are the best choice, since they prevent both the diffusion of the

cocktail into the wall of the vial and the absorption of radon from the environment. Glass vials exhibit

a considerably higher background and generally degrade the achievable alpha and beta discrimination.

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ISO 13165-1:2022(E)
7 Sampling

It is the responsibility of the laboratory to ensure the suitability of this test method for the water

samples tested.

Collect the sample in accordance with ISO 5667-1. Store the water sample (from 0,1 l to 1 l) in a bottle

(6.2.4) according to ISO 5667-3.

If necessary, carry out filtration immediately on collection and before acidification.

When pre-concentration is desired, acidify the sample to pH 1 to pH 3 with HNO (6.1.2).

The acidification of the water sample minimizes the loss of radioactive material from solution by

plating on the wall of the sample container. If filtration of the sample is required, the acidification is

performed afterwards, otherwise radioactive material already adsorbed on the particulate material

can be desorbed.

If the sample is not acidified, the sample preparation should start as soon as possible and always less

than one month after the sampling date (see ISO 5667-3).
8 Instrument set-up and calibration
8.1 Preparation of calibration sources
226

Transfer an accurately known mass, m , of the Ra standard solution (6.1.4) into a scintillation vial

226

(6.2.6). Let the massic activity of the Ra standard solution at the measuring time be a . Dilute with

water (6.1.1) to the previously chosen volume, for example, 10 ml. Add the scintillation cocktail (6.1.3),

for example, 10 ml.
Store the sample for at least 30 d to reach secular equilibrium.
Ensure that the diluted standard solutions are between pH 0 and pH 2.

Store samples so as to ensure optimum preservation. Storage in the dark is recommended. Select a

single generally applicable temperature in order not to affect distribution coefficients. This temperature

shall be consistent with the characteristics of the scintillation cocktail (6.1.3, see manufacturer's

instructions). Generally, if possible, storage in the scintillation chamber at around 15 °C is suitable.

8.2 Optimization of counting conditions

Set the alpha-counting window so that the energies of all the three alpha-emitters present in the

222 218 214

cocktail phase: Rn (5,49 MeV); Po (6,00 MeV); and Po (7,69 MeV); are covered. The observed

212
energy range should also include Po (8,78 MeV) as discussed in Clause 12.
226

Count the Ra calibration sample in alpha and beta-discrimination mode (see manufacturer

instructions) for an appropriate period, under different discriminator settings.

The best discriminator setting (working point) is chosen by visual inspection of the spectra in order to

obtain an alpha-spectrum free of beta counts (see Annex A).

NOTE Since no water is present in the scintillation cocktail phase, the quenching is low and constant, while

the alpha and beta discrimination is quite sharp.
8.3 Detection efficiency
226

Let the counting rate be r for the counts of the Ra calibration sample in the alpha-window, as

measured with the previously defined best discriminator setting.
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ISO 13165-1:2022(E)
Determine the relative alpha-efficiency given in Formula (1):
rr−
S 0
ε = (1)
Acceptance limits for efficiency should be defined.

NOTE The alpha-efficiency includes both counting and extraction efficiency. Usual values (in percent) are in

222 218 214
the range 200 % to 300 % ( Rn, Po and Po alpha-emissions).

It is advisable to check the linearity of the method. Assess the efficiency using calibration samples

whose activities cover the whole working range.

A more accurate estimate of efficiency can be obtained by preparing and measuring a sufficient number

of calibration samples.

Verify efficiencies at a periodicity established by the laboratory and whenever there are changes in

materials (e.g. scintillation cocktail) or when maintenance operations are performed on the scintillation

counter (6.2.5). A verification or a recalibration is necessary when the quality control requirements of

the instrument (see Clause 10) are not met.
8.4 Blank sample preparation and measurement

Acidify a laboratory water sample to between pH 0 and pH 2. Transfer the chosen quantity, for example,

10 ml, into the scintillation vial (6.2.6). Add the scintillation cocktail (6.1.3), for example, 10 ml, and mix

thoroughly.

Store the blank sample for 30 d and then count it using the chosen optimum counting conditions. Let

the measured counting rate in the alpha-window be r . If a preconcentration procedure is normally

employed, prepare blank samples by the same method.

Acceptance limits for blank samples should also be defined on the basis of the sensitivity desired. The

[12]
use of control charts (see ISO 7870-2 ) is advisable for this purpose.

It is recommended that blank samples be counted for the same period of time as the test portions.

Perform blank measurements at a periodicity established by the laboratory (e.g. monthly) and whenever

changes in materials (e.g. scintillation cocktail batch) or when maintenance operations are made on

the scintillation counter (6.2.5). Verification or a recalibration is necessary when instrument quality

control requirements (see Clause 10) are not met.
9 Procedure
9.1 Direct counting

Transfer a weighed (6.2.1) aliquot (m ) of the initial water sample (approximately 50 g) into a beaker. If

the sample has not yet been acidified, adjust to pH 0 and pH 2 using nitric acid (6.1.2) and verify with a

pH-meter (6.2.3).

Heat to approximately 80 °C under stirring for 30 min in a covered beaker, to allow degassing of

222

dissolved Rn. Allow the sample to cool and reweigh it to account for loss due to evaporation (m ).

9.2 Thermal preconcentration

Thermal preconcentration can be used when soft waters are examined (e.g. dry residue <500 mg·l , as

in most drinking waters) in order to decrease the detection limit of the method. Hard waters can give

rise to salt precipitations wh
...

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