SIST EN ISO 9698:2019

SLOVENSKI STANDARD
01-julij-2019
Nadomešča:
SIST EN ISO 9698:2015
SIST ISO 9698:2013
Kakovost vode - Tritij - Preskusna metoda s štetjem s tekočinskim scintilatorjem
(ISO 9698:2019)
Water quality - Tritium - Test method using liquid scintillation counting (ISO 9698:2019)
Wasserbeschaffenheit - Tritium - Verfahren mit dem Flüssigszintillationszähler (ISO
9698:2019)
Qualité de l'eau - Tritium - Méthode d'essai par comptage des scintillations en milieu
liquide (ISO 9698:2019)
Ta slovenski standard je istoveten z: EN ISO 9698:2019
ICS:
13.060.60 Preiskava fizikalnih lastnosti Examination of physical
vode properties of water
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 9698
EUROPEAN STANDARD
NORME EUROPÉENNE
May 2019
EUROPÄISCHE NORM
ICS 13.060.60; 13.280 Supersedes EN ISO 9698:2015
English Version
Water quality - Tritium - Test method using liquid
scintillation counting (ISO 9698:2019)
Qualité de l'eau - Tritium - Méthode d'essai par Wasserbeschaffenheit - Tritium - Verfahren mit dem
comptage des scintillations en milieu liquide (ISO Flüssigszintillationszähler (ISO 9698:2019)
9698:2019)
This European Standard was approved by CEN on 30 April 2019.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey 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
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 9698:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 9698:2019) has been prepared by Technical Committee ISO/TC 147 "Water
quality" in collaboration with Technical Committee CEN/TC 230 “Water analysis” the secretariat of
which is held by DIN.
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 November 2019, and conflicting national standards
shall be withdrawn at the latest by November 2019.
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.
This document supersedes EN ISO 9698:2015.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 9698:2019 has been approved by CEN as EN ISO 9698:2019 without any modification.

INTERNATIONAL ISO
STANDARD 9698
Third edition
2019-05
Water quality — Tritium — Test
method using liquid scintillation
counting
Qualité de l'eau — Tritium — Méthode d'essai par comptage des
scintillations en milieu liquide
Reference number
ISO 9698:2019(E)
©
ISO 2019
ISO 9698:2019(E)
© ISO 2019
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
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Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2019 – All rights reserved

ISO 9698:2019(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 2
4 Principle . 2
5 Reagents and equipment . 3
5.1 Reagents. 3
5.1.1 Water for the blank . 3
5.1.2 Calibration source solution . 4
5.1.3 Scintillation solution. 4
5.1.4 Quenching agent. 4
5.2 Equipment . 4
5.2.1 General. 4
5.2.2 Liquid scintillation counter . 5
5.2.3 Counting vials . 5
6 Sampling and samples . 5
6.1 Sampling and sample transportation . 5
6.2 Sample storage . 6
7 Procedure. 6
7.1 Sample preparation . 6
7.1.1 General. 6
7.1.2 Direct procedure . 6
7.1.3 Distillation . 6
7.2 Preparation of the sources to be measured . 6
7.3 Counting procedure . 7
7.3.1 General. 7
7.3.2 Control and calibration. 7
7.3.3 Measurement conditions . 8
7.3.4 Interference control . 8
8 Expression of results . 9
8.1 General . 9
8.2 Calculation of activity concentration . 9
8.3 Decision threshold .10
8.4 Detection limit .10
8.5 Confidence interval limits.11
8.6 Calculations using the activity per unit of mass .11
9 Test report .11
Annex A (informative) Numerical applications .13
Annex B (informative) Distillation of large volume sample .14
Annex C (informative) Internal standard methods .17
Annex D (informative) Distillation of small volume sample .19
Annex E (informative) Simplified distillation .22
Bibliography .24
ISO 9698:2019(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 third edition cancels and replaces the second edition (ISO 9698:2010), which has been technically
revised. The main changes compared to the previous edition are as follows:
— the Introduction has been developed;
— the Scope has been updated;
— the sample preparation has been revised;
— the Bibliography has been enhanced.
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 2019 – All rights reserved

ISO 9698:2019(E)
Introduction
Radioactivity from several naturally-occurring and anthropogenic sources is present throughout
the environment. Thus, water bodies (e.g. 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
226 228 234 238 210
uranium decay series, in particular Ra, Ra, U, U, 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 fertilizer production and use).
— Human-made 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 the 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 installation during planned, existing and emergency exposure situations . Drinking water
may thus contain radionuclides at activity concentrations which could present a risk to human health.
The radionuclides present in liquid effluents are usually controlled before being discharged into the
[2]
environment . Water bodies and 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 water bodies 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 a planned or existing situation, the WHO
−1 3
guidelines for guidance level in drinking water is 10 000 Bq·l for H activity concentration.
NOTE 1 The guidance level 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
[3]
very low level of risk and which is not expected to give rise to any detectable adverse health effects .
[5]
In the event of a nuclear emergency, the WHO Codex guideline levels mentioned that the activity
−1 −1
concentration might not be greater than 1 000 Bq·l for infant food and 10 000 Bq·l for food other
than infant food, including organically bound tritium.
NOTE 2 The Codex guidelines levels (GLs) apply to radionuclides contained in food 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 food, and are based on an intervention exemption level of 1 mSv in a year for members of the public
[5]
(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 .
ISO 9698:2019(E)
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 discharge to the environment. 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 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
could increase the overall uncertainty, detection limit, and threshold.
The test method 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 may have 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.
vi © ISO 2019 – All rights reserved

INTERNATIONAL STANDARD ISO 9698:2019(E)
Water quality — Tritium — 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
This document specifies a method by liquid scintillation counting for the determination of tritium
activity concentration in samples of marine waters, surface waters, ground waters, rain waters,
drinking waters or of tritiated water ([ H]H O) in effluents.
The method is not directly applicable to the analysis of organically bound tritium; its determination
requires additional chemical processing of the sample (such as chemical oxidation or combustion).
−1
With suitable technical conditions, the detection limit may be as low as 1 Bq·l . Tritium activity
6 −1
concentrations below 10 Bq·l can be determined without any sample dilution.
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/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
me a s ur ement (GUM: 1995)
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated
terms (VIM)
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
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the definitions, symbols and abbreviations given in ISO/IEC Guide 99,
ISO/IEC Guide 98-3, ISO 80000-10 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https: //www .iso .org/obp
ISO 9698:2019(E)
— IEC Electropedia: available at http: //www .electropedia .org/
3.1.1
effluent
water or wastewater discharged from a containing space such as a treatment plant, industrial process
or lagoon
3.2 Symbols
For the purposes of this document, the symbols given in ISO/IEC Guide 99, ISO/IEC Guide 98-3,
ISO 80000-10 and the following apply.
Symbol Definition Unit
β Maximum energy for the beta emission keV
max
V Volume of test sample l
m Mass of test sample, kg
−1
ρ Density of the sample kg∙l
−1
c Activity concentration, in Bq∙l
A
−1
a Activity per unit of mass Bq∙kg
A Activity of the calibration source Bq
n Number of counting
t Background counting time s
t Sample counting time s
g
t Calibration counting time s
s
−1
r Background count rate s
−1
r Sample count rate s
g
−1
r Calibration count rate s
s
ε Detection efficiency
f Quench factor
q
−1
u(c ) Standard uncertainty associated with the measurement result Bq∙l
A
−1
U Expanded uncertainty, calculated by U = k · u(c ) with k = 1, 2,…, Bq∙l
A
*
Decision threshold
−1
c Bq∙l
A
#
Detection limit
−1
c Bq∙l
A

Lower and upper limits of the confidence interval
−1
cc, Bq∙l
AA
4 Principle
The test portion is mixed with the scintillation cocktail in a counting vial to obtain a homogeneous
medium. Electrons (Beta particles) emitted by tritium transfer their energy to the scintillation medium.
Molecules excited by this process return to their ground state by emitting photons that are detected by
[8]
photodetectors .
The choice of the analytical procedure (either with or without distillation of the water sample prior to
[19][20][21]
determination), depends on the aim of the measurement and the sample characteristics .
[8]
Direct measurement of a raw water sample using liquid scintillation counting shall consider the
potential presence of other beta emitter radionuclides. To avoid interference with these radionuclides
when they are detected, the quantification of tritium is performed following the sample treatment by
[22][23][24][25]
distillation . Annexes B, D and E describe three distillation procedures.
2 © ISO 2019 – All rights reserved

ISO 9698:2019(E)
In order to determine the background count rate, a blank sample is prepared in the same way as the
test portion. The blank sample is prepared using a reference water of the lowest activity available, also
sometimes called “dead water”.
In order to determine the detection efficiency, it is necessary to measure a water sample having a
known tritium activity under conditions that are identical to those used for the test sample. This water
shall be a dilution of this mixture produced with the reference water, or a water with a traceable tritium
activity usable without dilution.
The conditions to be met for the blank sample, the test portion and the calibration source are:
— same scintillation cocktail;
— same type of counting vial;
— same filling geometry;
— same ratio between test portion and scintillation cocktail;
— temperature stability of the detection equipment;
— value of quench indicating parameter included in calibration curve.
If particular conditions of chemical quenching affect the measurement results, it is recommended to
correct the counting data using a quench curve (see 7.3.2).
5 Reagents and equipment
Use only reagents of recognized analytical grade.
5.1 Reagents
5.1.1 Water for the blank
The water used for the blank shall be as free as possible of chemical impurities to avoid quenching,
[26][27]
of radioactive impurities and with an activity concentration of tritium negligible in comparison
with the activities to be measured.
For example, a water sample with a low tritium activity concentration can be obtained from (deep)
subterranean water kept in a well-sealed borosilicate glass bottle in the dark at controlled temperature
(see ISO 5667-3). This blank water sample shall be kept physically remote from any tritium containing
material.
It is advisable to keep an adequate quantity of blank water in stock and to make small working amounts
from it for immediate use as required. Contamination with tritium (e.g. from water vapour in the air
and from tritium sources such as luminous watches and gas chromatographs) or other radioactive
species should be avoided.
−1
Determine the tritium activity concentration, in Bq·l , of this water and note the date of the
determination.
−1
As the activity is becoming non-negligible for activities around 1 Bq·l , it is necessary to use a blank
water measured to ensure the “absence” of tritium. The tritium activity concentration in the blank water
can be determined by enrichment followed by liquid scintillation counting or from the measurement of
He by mass spectrometry. Preferably use blank water with a tritium activity concentration of less than
−1
0,5 Bq·l .
When the volume of blank water is sufficiently large, e.g. 10 l to 20 l, and well-sealed, tritium activity
concentration should remain stable for years, although it is advisable to verify this activity concentration
at predetermined intervals, e.g. every year.
ISO 9698:2019(E)
5.1.2 Calibration source solution
In order to avoid cross-contamination, prepare, in a suitable location which is remote from the area
where the tritium analyses are to be carried out, weigh and pour into a weighed volumetric flask (for
example, 100 ml) the requisite quantity of a concentrated tritium ([ H]H O) standard solution, so that
the tritium activity concentration generates sufficient counts to reach the required measurement
uncertainty after dilution with blank water and thorough mixing. Calculate the tritium activity
concentration of the resulting calibration source solution (t = 0). Note the date at which the standard
solution was made up (t = 0).
The tritium activity concentration of the calibration source solution at time t at which the samples are
measured shall be corrected for radioactive decay.
It is recommended to adapt the flask to the standard source volume so as to not leave air above its
surface, in order to minimize the exchange of tritium with the atmosphere at each opening of the flask.
5.1.3 Scintillation solution
The scintillation cocktail is chosen according to the characteristics of the sample to be analysed and
[28]
according to the properties of the detection equipment .
It is recommended to use a hydrophilic scintillation cocktail for the measurement of environmental
water or waste water.
The characteristics of the scintillation cocktail shall ensure the mixture is homogeneous and stable at
the given mixing ratio and at the temperature of the counting system.
For the direct measurement of raw waters containing particles in suspension, it is recommended to use
a scintillation cocktail leading to a gel type mixture.
It is recommended to
— store the scintillation cocktail in the dark and, particularly just before counting, avoid exposure to
direct sunlight or fluorescent light in order to prevent interfering luminescence, and
— comply with storage conditions specified by the scintillation cocktail supplier.
The mixtures (scintillation cocktail and test sample) should be disposed of as chemical waste, and,
depending on the radioactivity, may require disposal as radioactive waste.
5.1.4 Quenching agent
Examples of chemical quenching agents include nitric acid, acetone, organochloride compounds,
nitromethane, etc.
NOTE Some quenching agents are dangerous or toxic.
5.2 Equipment
5.2.1 General
Laboratory equipment, such as pipettes and balances, shall be employed that enables the expected/
agreed data quality objectives to be achieved, as well as the quantification of the uncertainty attached
to the measurement.
Control of the quantity of liquid scintillation cocktail used in source preparation is essential to achieve
consistent data quality.
4 © ISO 2019 – All rights reserved

ISO 9698:2019(E)
5.2.2 Liquid scintillation counter
Liquid scintillation counter preferably with an automatic sample transfer. Operation at constant
temperature is recommended following the manufacturer's instructions. Depending on the limit of
detection to be reached, a liquid scintillation counter with a low-level-configuration may be needed.
The method specified in this document relates to the widely used liquid scintillation counters with
vials that hold about 20 ml. When other vials are used with appropriate counters, the described method
shall be adapted accordingly.
5.2.3 Counting vials
Different types of scintillation vials exist, manufactured using a range of materials. The most common
are glass vials and polyethylene vials. Glass vials allow visual inspection of the scintillation medium,
but have an inherent background, due to the presence of K. However, some organic solvents contained
in scintillation cocktails diffuse through the polyethylene, accelerating the degradation of the mixture.
Other types of vials that exist are the following:
— glass vials with a low level of K, exhibit a lower background than ‘normal’ glass vials;
— for the determination of very low tritium concentration, the use of polytetrafluoroethylene vials
(PTFE) or polyethylene vials with an inner layer of PTFE on inside vial wall is strongly recommended.
Diffusion of organic solvents is then slower through PTFE than through polyethylene. These vials
are used for long counting times with very low-level activity to be measured.
Generally, the vials are single use. If the vial is re-used, it is necessary to apply an efficient cleaning
procedure.
To prevent interfering luminescence, the counting vials should be kept in the dark and should not be
exposed to direct sunlight or fluorescent light, particularly just before counting.
Toluene-based scintillation solutions may physically distort polyethylene and should therefore not be
used in combination with polyethylene counting vials. Diffusion of organic solvents into and through
the polyethylene walls is also a serious drawback of polyethylene vials.
6 Sampling and samples
6.1 Sampling and sample transportation
Conditions of sampling shall conform to ISO 5667-1. Preservation and handling of water samples shall
be in accordance with ISO 5667-3. Additional information on sampling of different types of waters can
[9][10][11][12][13][14][15][16]
be found in the relevant parts of ISO 5667 . Additional information on quality
[17]
assurance of environmental water sampling and handling is given in ISO 5667-14 .
The sample shall not be acidified due to the high chemical quench caused by acids, and the potential
presence of tritium in the acid (as specified in ISO 5667-3).
It is important that the laboratory receives a representative sample, unmodified during the transport
or storage and in an undamaged container. To avoid compromising the sample, it is recommended to
use plastic containers for effluents and glass containers for other types of samples. The glass containers
reduce the risk of cross contamination. The plastic containers limit the risk of breakage and spilling of
effluents, which may contain high activity concentrations of radionuclides.
For low level activity measurements, it is important to minimize contact between the sample and the
atmosphere during the sampling.
It is recommended to fill the container completely, leaving no headspace to minimize tritium exchange
with the atmospheric moisture.
ISO 9698:2019(E)
6.2 Sample storage
If needed, the samples shall be stored in compliance with ISO 5667-3. If the storage duration exceeds
three months as recommended in ISO 5667-3, it is advisable to store the samples in glass containers.
For liquid effluents, it is recommended to store separately the samples with high, medium and low level
tritium activity concentrations.
7 Procedure
7.1 Sample preparation
7.1.1 General
A monitoring program should be part of the laboratory quality system, in order to detect any potential
cross contamination between samples with widely varying activity concentrations. The ambient air of
the laboratory should be monitored for tritium, for example by measuring condensed humidity, free
surface water from open vial, etc. or carrying out specific studies demonstrating the absence of risk of
cross contamination.
[27][28][29][30]
A prior enrichment step can significantly lower the limit of detection .
7.1.2 Direct procedure
Measurement of the test sample is generally performed on raw water without removal of suspended
matter. If the activity of a filtered or centrifuged sample is to be measured, the removal of suspended
matter shall be performed as soon as possible after the sampling (see ISO 5667-3).
7.1.3 Distillation
Examples of distillation procedures are given in Annexes B, D and E.
[31][32]
Distillation shall avoid isotopic fractionation . The yield of the distillation method shall be verified
by analysing a tritium certified standard solution, or at least a known activity concentration water, in
the same way as the portion test sample.
Distillation or any other physic-chemical treatment of water is not appropriate for simultaneous
3 14
measurement of H and C.
7.2 Preparation of the sources to be measured
A known quantity of the test sample and the scintillation cocktail are introduced into the counting vial.
After closing the vial, it shall be thoroughly shaken to homogenize the mixture.
The vial identification shall be indicated on the top of the vial cap. The storage time depends upon the
scintillation mixture, the mixture stability and the nature of the sample. It is recommended to perform
the measurement as soon as any photoluminescence or static electricity effects have become negligible,
for example, after 12 h.
In order to reduce photoluminescence effects, it is recommended that the above-mentioned operations
take place in dimmed light (preferably light from an incandescent source or UV-free LED or red light);
in addition one should avoid direct sunlight or fluorescent light.
In order to reduce static electricity effects, the vial can be sprayed with an antistatic agent or wiped
with a moist tissue.
6 © ISO 2019 – All rights reserved

ISO 9698:2019(E)
7.3 Counting procedure
7.3.1 General
The measurement conditions (measurement time, blank sample, number of cycles or repetitions) are
defined according to the uncertainty and detection limit to be achieved.
7.3.2 Control and calibration
Statistical control of the detection system shall be monitored by measurement of suitable reference
background and reference sources usually provided by the equipment supplier, for example in
[18]
compliance with ISO 7870-2 .
The correct operation of the counter shall be checked periodically by means of reference sources which
cover the energy range to be measured.
The background is measured prior to each measurement or each series of measurements of samples,
under the conditions representative of each type of measurement (Clause 4).
The detection efficiency is determined with a sample of a standard of aqueous tritium (calibration
source), or a dilution of this standard with water for the blank, measured in the same conditions as the
test portion.
Using direct measurement, it is essential to generate a quench curve for each type of water measured.
The quench curve is valid only for:
— a given type of measurement equipment;
— a given type of scintillation cocktail;
— a given ratio of scintillation cocktail and test sample.
Particular conditions of chemical quenching affect the measurement results, thus it is recommended to
correct the counting data using a quench curve. It is important to choose a chemical quenching agent
similar to the quenching observed in the sample. The quench curve correction is not applicable to colour
quenched samples.
The quench curve is obtained with a series of working standards (10 for example), presenting different
quench. The matrix of the working standards is representative of matrix of the samples to be measured
(same scintillation liquid, same ratio scintillation liquid-test sample). The working standards may be
prepared as follows.
— Similar quantity of certified standard tritiated water solution in each vial. The activity of the
certified standard shall be sufficient for the counting ratio to be defined with a known statistical
precision, even in the case of a strong quench.
— The standard is completed with reference water until the volume of test sample is reached.
— The scintillation cocktail is added to obtain the desired ratio.
— One working standard at least is used as it is. In the other working standards, increasing quantities
of quenching agent are added to simulate the quench encountered in the samples to be measured.
The quench curve relating ε·f with the quenching is used to determine f .
q q
For high activity and highly quenched samples or colour quenched samples, it may be practical to use
an internal standard method, as described in Annex C.
ISO 9698:2019(E)
7.3.3 Measurement conditions
The counting room used shall be suitable for the measurement equipment and to the activity levels of
the samples.
The measurement is performed using an energy window that is between the detector noise threshold
and the β of tritium (18,6 keV). It is recommended to choose the width of the energy window in
max
 
ε
order to optimize the figure of merit .
 
r
 0 
The absence of other radionuclides is verified by checking the counting rate above the maximum energy
β of the tritium.
max
In order to verify the statistical distribution of counting data, it is recommended to arrange the
counting as repetitions: the first sample is counted several times in a row (number of repetitions), then
the second sample is counted likewise, and so on.
To measure low activities, it is recommended to fractionate the counting as cycles: all samples are
counted once, then the
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