EN ISO 22908:2020

SLOVENSKI STANDARD
01-maj-2020
Kakovost vode - Radij Ra-226 in Ra-228 - Preskusna metoda s štetjem s
tekočinskim scintilatorjem (ISO 22908:2020)
Water quality - Radium 226 and Radium 228 - Test method using liquid scintillation
counting (ISO 22908:2020)
Wasserbeschaffenheit - Radium-226 und Radium-228 - Verfahren mit dem
Flüssigszintillationszähler (ISO 22908:2020)
Qualité de l'eau - Radium 226 et radium 228 - Méthode d'essai par comptage des
scintillations en milieu liquide (ISO 22908:2020)
Ta slovenski standard je istoveten z: EN ISO 22908:2020
ICS:
13.060.50 Preiskava vode na kemične Examination of water for
snovi chemical substances
17.240 Merjenje sevanja Radiation measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 22908
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2020
EUROPÄISCHE NORM
ICS 13.060.60; 13.280; 17.240
English Version
Water quality - Radium 226 and Radium 228 - Test
method using liquid scintillation counting (ISO
22908:2020)
Qualité de l'eau - Radium 226 et radium 228 - Méthode Wasserbeschaffenheit - Radium-226 und Radium-228 -
d'essai par comptage des scintillations en milieu Verfahren mit dem Flüssigszintillationszähler (ISO
liquide (ISO 22908:2020) 22908:2020)
This European Standard was approved by CEN on 20 December 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, 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
© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 22908:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 22908:2020) 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 August 2020, and conflicting national standards shall
be withdrawn at the latest by August 2020.
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.
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, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the
United Kingdom.
Endorsement notice
The text of ISO 22908:2020 has been approved by CEN as EN ISO 22908:2020 without any modification.

INTERNATIONAL ISO
STANDARD 22908
First edition
2020-01
Water quality — Radium 226 and
Radium 228 — Test method using
liquid scintillation counting
Qualité de l'eau — Radium 226 et radium 228 — Méthode d'essai par
comptage des scintillations en milieu liquide
Reference number
ISO 22908:2020(E)
©
ISO 2020
ISO 22908:2020(E)
© ISO 2020
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
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
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 2020 – All rights reserved

ISO 22908:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and units . 1
3.1 Terms and definitions . 1
3.2 Symbols, definitions and units . 2
4 Principle . 3
5 Reagents and equipment . 3
5.1 Reagents. 3
5.2 Equipment . 4
6 Sampling . 5
7 Instrument set-up and calibration . 5
7.1 Optimization of counting conditions . 5
7.1.1 Preparation of sources . 5
7.1.2 Optimization process . 6
226 228
7.2 Counting efficiencies of Ra and Ra . 6
226 228
7.2.1 Preparation of Ra and Ra standard sources . 6
7.2.2 Determination of counting efficiencies . 6
7.3 Blank sample measurement . 7
8 Procedure. 7
8.1 General . 7
8.2 Separation of radium by precipitation . 7
8.3 Purification of radium . 8
8.4 Test sample preparation . 8
8.5 Measurement . 9
8.6 Chemical recovery . 9
8.6.1 General. 9
226 228
8.6.2 Preparation of a QC sample with known Ra and Ra activities . 9
8.6.3 Determination of overall counting efficiencies . 9
8.6.4 Determination of chemical recovery . 9
9 Quality control .10
10 Expression of results .10
226 228
10.1 Calculation of massic activities of Ra and Ra at the sampling date .10
10.2 Standard uncertainty .10
10.3 Decision threshold .12
10.4 Detection limit .12
10.5 Confidence limits.12
11 Interference control .12
12 Test report .13
Annex A (informative) Flow chart of the procedure .14
Annex B (informative) Decay series relevant to radium isotopes .15
Annex C (informative) Set-up parameters and procedure .16
Annex D (informative) Validation data.22
Bibliography .28
ISO 22908:2020(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 on 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 the following
URL: www .iso .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 147, Water quality, Subcommittee SC 3,
Radioactivity measurements.
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 2020 – All rights reserved

ISO 22908:2020(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 uranium
226 228 234 238 210
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 fertilizers 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 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 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
[2]
the environment and water bodies. Drinking waters are monitored for their radioactivity 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 a planned or existing situation, the WHO
226 228
guidelines for guidance level in drinking water are 1 Bq/l and 0,1 Bq/l, for Ra and Ra activity
concentrations, respectively.
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
concentrations might be greater.
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 foods, and are based on an intervention exemption level of 1 mSv in a year for members of the
[5]
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 .
ISO 22908:2020(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 being discharged 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(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
could 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 support 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 2020 – All rights reserved

INTERNATIONAL STANDARD ISO 22908:2020(E)
Water quality — Radium 226 and Radium 228 — Test
method using liquid scintillation counting
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 according to this document be
carried out by suitably trained staff.
1 Scope
226 228
This document specifies the determination of radium-226 ( Ra) and radium-228 ( Ra) activity
concentrations in drinking water samples by chemical separation of radium and its measurement using
liquid scintillation counting.
226 228
Massic activity concentrations of Ra and Ra which can be measured by this test method utilizing
currently available liquid scintillation counters go down to 0,01 Bq/kg for Ra and 0,06 Bq/kg for
228 [8]
Ra for a 0,5 kg sample mass and a 1 h counting time in a low background liquid scintillation counter .
The test method can be used for the fast detection of contamination of drinking water by radium in
emergency situations.
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 17025:2017, 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, definitions, symbols and units
3.1 Terms and definitions
No terms and definitions are listed in this document.
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
— IEC Electropedia: available at http:// www .electropedia .org/
ISO 22908:2020(E)
3.2 Symbols, definitions and units
For the purposes of this document, the definitions, symbols and abbreviations given in ISO 80000-10,
ISO/IEC Guide 98-3, and the following apply.
Symbol Unit Definition
A Bq/kg Certified massic activity of the analyte in the certified standard solution at the
x
reference date
t
Bq/kg Massic activity of the analyte in the quality control sample at the reference date
A
x
a Bq/kg Massic activity of the analyte in the test sample at the sampling date
x
a* Bq/kg Decision threshold of the analyte
#
a Bq/kg Detection limit of the analyte
⊲ ⊳
a , a Bq/kg Lower and upper limits of the confidence interval
c Bq/l Activity concentration of the analyte in the test sample at the sampling date
a
C Bq/kg Target massic activity of the analyte in the quality control sample prepared
x
for the validation of the procedure
m kg Mass of the certified standard solution taken for the analysis of the analyte
s-x
m kg Mass of the quality control sample taken for the analysis of the analyte
t-x
m kg Mass of the test sample
s
s
1/s Net count rate of the analyte in the certified standard solution
n
x
t
1/s Net count rate of the analyte in the quality control sample
n
x
n 1/s Net count rate of the analyte in the test sample
x
PI % Precision index
R Bq/kg Reproducibility limit
L
r Bq/kg Repeatability limit
L
r 1/s Gross count rate of the analyte in the test sample
g−x
r 1/s Gross count rate of the analyte in the blank sample
0-x
S Bq/kg Standard deviation of repeatability
r
S Bq/kg Standard deviation of reproducibility
R
T s Counting time of the analyte in the test sample
s-x
t s Counting time of the analyte in the blank
0-x
t s Time interval between measurement date and reference date of the analyte
s-x
in the certified standard solution
t s Time interval between measurement date and reference date of the analyte
t-x
in the quality control sample
t s Time interval between measurement date and sampling date of the analyte
x
in the test sample
u(a) Bq/kg Standard uncertainty associated with the measurement result
u(x) Bq/kg Uncertainty in quantity x
U Bq/kg Expanded uncertainty, calculated using U = ku(a), with k = 1, 2,…
w 1/kg Factor equal to 1/ε m
x s
ε — Counting efficiency of the analyte
x
c
— Overall efficiency of the analyte in the quality control sample
ε
x
λ 1/s Decay constant of the analyte
x
Bq/kg Mean of all measured values of the analyte in the quality control sample
Χ
x
for the validation of the procedure
δ % Relative bias of the method
ρ kg/l Density
2 © ISO 2020 – All rights reserved

ISO 22908:2020(E)
4 Principle
Barium co-precipitation is used as a method of separation for radium due to the very similar chemical
properties of barium and radium. The exploitation of the ability of barium to react with an excess
of sulfate ions to produce a precipitate allows the quantitative analysis of environmental activity
concentrations of radium in water. The inclusion of a lead hold-back carrier allows the removal of Pb
228 210
from solution, which increases the accuracy of Ra measurement, as Pb can produce a spectral
interference. The removal of Pb is achieved by lowering the pH of the solution to re-precipitate
barium sulfate using acetic acid in which lead sulfate is soluble. This allows Pb to remain in solution
and therefore be removed.
The source preparation is achieved by suspending the barium sulfate precipitate in the EDTA
solution. Barium sulfate is insoluble in water, alkalis and acids, but EDTA increases the solubility due
to the complexation of barium and the speciation effect. The EDTA molecule inhibits barium sulfate
nucleation. This enables the use of a naphthalene-based scintillation cocktail to gain better spectral
resolution than with the use of a gel-forming cocktail.
The flow chart of the procedure is given in Annex A.
226 228
Massic activities of Ra and Ra in the sample are calculated from net count rates of the sample
source, sample amount and the overall efficiency that can be obtained from spiked sample with known
226 228
activities of Ra and Ra, and that shows the ability of the method to extract radium (chemical
recovery) as well as the ability (counting efficiency) of the instrument to detect it.
/
The test method applies to the analysis of a test sample of drinking water containing less than 100 mg
kg barium. If the barium concentration is higher than 100 mg/kg, it is recommended to reduce the
volume of the test sample to be analysed so that the total content of barium in the sample does not
exceed 50 mg.
NOTE Adjustment of the test sample mass and counting time can lead to lower detection limits. As an
example, a limit of detection of 0,04 Bq/kg can be achieved for Ra using a 0,5 kg test sample and a 2 h counting
time; similarly a limit of detection of 0,02 Bq/kg can be achieved for Ra using a 1 kg test sample and a 2 h
counting time.
5 Reagents and equipment
5.1 Reagents
All reagents shall be of recognized analytical grade and, except for 5.1.12, 5.1.13 and 5.1.14, shall not
contain any detectable alpha- and beta-activity.
5.1.1 Laboratory water, distilled or deionized, in conformance with ISO 3696, grade 3.
5.1.2 Lead carrier solution prepared using 2,397 g lead nitrate, 0,5 ml nitric acid solution (5.1.4) and
made up to 100 ml with laboratory water (5.1.1).
5.1.3 Barium carrier solution prepared using 2,836 g barium chloride, 0,5 ml nitric acid solution
(5.1.4) and made up to 100 ml laboratory water (5.1.1).
5.1.4 Nitric acid solution, c(HNO ) = 15,8 mol/l, ρ = 1,42 g/ml, w(HNO ) = 700 g/kg.
3 3
5.1.5 Hydrochloric acid solution, c(HCl) = 10,2 mol/l, ρ = 1,16 g/ml, w(HCl) = 320 g/kg.
5.1.6 Sulfuric acid solution, c(H SO ) =9,2 mol/l, ρ = 1,84 g/ml, w(H SO ) = 980 g/kg.
2 4 2 4
5.1.7 Ammonia solution, c(NH ) = 13,4 mol/l, ρ = 0,91 g/ml, w(NH ) = 250 g/kg.
3 3
ISO 22908:2020(E)
5.1.8 Glacial acetic acid solution, c(CH COOH) = 16,8 mol/l, ρ = 1,05 g/ml, w(CH COOH) = 960 g/kg.
3 3
5.1.9 Ethylenediaminetetraacetic acid (EDTA), M(EDTA) = 292,2 g/mol.
NOTE For the purposes of this document, an EDTA solution warmed up within the 60 °C–80 °C temperature
range is considered as a hot EDTA solution.
5.1.10 Analytical grade ammonium sulfate, M((NH ) SO ) = 132,1 g/mol.
4 2 4
5.1.11 Scintillation cocktail, commercially available scintillation cocktail, water immiscible and
suitable for alpha and beta discrimination (e.g. diisopropylnaphthalene-based cocktails).
226 228
5.1.12 Ra and Ra standard solutions
Radium-226 and Ra standard solutions shall be provided with calibration certificates containing
at least the activity concentration, measurement uncertainty and statement of compliance with an
identified metrological specification.
241 210 242
5.1.13 Alpha emitter standard solution ( Am or Po or Pu)
The alpha emitter standard solution shall be provided with calibration certificate containing at least
the activity concentration, measurement uncertainty and statement of compliance with an identified
metrological specification.
90 90 36
5.1.14 Beta emitter standard solution ( Sr/ Y or Cl)
The beta emitter standard solution shall be provided with calibration certificate containing at least
the activity concentration, measurement uncertainty and statement of compliance with an identified
metrological specification.
5.2 Equipment
5.2.1 Standard laboratory equipment.
5.2.2 Analytical balance with accuracy of 0,1 mg.
5.2.3 Hotplate with a magnetic stirrer and a stirring bar.
5.2.4 Centrifuge, with a revolution rate of 3 500 r/min.
5.2.5 pH-meter or pH papers.
5.2.6 Water bath with temperature controller.
5.2.7 Vortex mixer.
5.2.8 Wide-mouth HDPE sample bottles, volumes between 500 ml and 1 l.
5.2.9 Glass beaker, volume of 600 ml.
5.2.10 Centrifuge tubes, volume of 50 ml, made of HDPE or PP.
5.2.11 Precision pipettes, volumes of 50 μl, 5 ml and 10 ml.
4 © ISO 2020 – All rights reserved

ISO 22908:2020(E)
5.2.12 Elemental analysis technique for barium and calcium determination.
5.2.13 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.
5.2.14 Polyethylene scintillation vials, PTFE coated, 20 ml.
PTFE-coated polyethylene vials are recommended because they prevent the diffusion of the cocktail
into the wall of the vial. Glass vials exhibit a considerably higher background and generally degrade the
achievable alpha and beta discrimination.
5.2.15 Transfer pipette
6 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 in a plastic bottle (5.2.8)
according to ISO 5667-3. If necessary, carry out filtration immediately on collection and before
acidification.
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 1 month after the sampling date (ISO 5667-3).
226 228 238 232
NOTE Ra and Ra are present in the environment as radionuclides from the U and Th decay
226 228
series, as shown in Annex B. Massic activity concentrations of Ra and Ra can vary widely according to
[9] 226
local geological and climatic characteristics . Ra massic activity concentration ranges from some mBq/kg in
[10] 228
surface waters up to several tens of Bq/kg in some natural groundwaters . Ra massic activity concentration
[10]
ranges from a few mBq/kg in surface waters up to several Bq/kg in some natural groundwaters .
7 Instrument set-up and calibration
7.1 Optimization of counting conditions
7.1.1 Preparation of sources
Add 2 ml of barium carrier solution (5.1.3) to two 50 ml volume HDPE or PP centrifuge tubes (5.2.10)
using a precision pipette (5.2.11).
Add 3 ml of 100 g/kg ammonium sulfate solution (5.1.10) and 1 ml of ammonia solution (5.1.7) to
each solution using precision pipettes (5.2.11) to obtain the barium sulfate precipitates. Separate the
precipitates by centrifuging for 5 minutes at 3 500 r/min (5.2.4).
Dissolve the precipitates in 4 ml of hot 0,25 mol/l EDTA solution (5.1.9) using a precision pipette
(5.2.11) and agitate the solutions carefully to dissolve and suspend the precipitates into solution. This
may require the use of a vortex mixer (5.2.7).
Quantitatively transfer the solutions including partially dissolved barium sulfate precipitate to two
20 ml plastic liquid scintillation vials (5.2.14) using transfer pipettes.
Rinse the HDPE or PP centrifuge tubes with another 1 ml of hot 0,25 mol/l EDTA solution (5.1.9) to
ensure that no analyte remains in the tubes.
ISO 22908:2020(E)
Add 14 ml of liquid scintillation cocktail (5.1.11) to each plastic liquid scintillation vial (5.2.14) and
vortex or shake well until each solution appears homogenous. The addition of the cocktail should be
done all at once or in large portions to avoid any reaction with the source solution that could cause a
cloudy, inhomogeneous mixture.
Add (10 to 100) Bq of alpha emitter (5.1.13) in the first vial and add (10 to 100) Bq of beta emitter
(5.1.14) in the second vial in 50 μl volume solutions using a precision pipette (5.2.11).
Seal and shake the LSC sources until the suspensions appear homogenous.
Clean the vials with an alcohol wipe to remove any static interference.
7.1.2 Optimization process
Select the full range of the instrument from channel 0 to channel 1024.
Count the calibration sources in alpha and beta-discrimination mode (see the manufacturer’s
instructions) for an appropriate period, at different discrimination factors.
Calculate the number of alpha counts in the beta counting mode and the number of beta counts in the
alpha counting mode.
Make a graph of the correlation between spillover and discrimination factor.
The best discrimination factor (working point) is chosen by visual inspection of the graph in order to
obtain a beta-spectrum free of alpha counts (see Annex C).
NOTE The determination of an optimum discrimination factor requires two standards, one pure alpha and
241 210 242 90 90 36
one pure beta emitter, Am or Po or Pu and Sr/ Y or Cl, respectively. These radionuclides are used
226 228
rather than Ra and Ra, as the latter are accompanied by progeny in-growth, which creates uncertainty in
the determination of a discrimination factor.
Select the best discrimination factor to carry out the test method.
Set the lower and upper limits of the analysis windows region using the known emission energies of
226 228
Ra and Ra.
226 228
7.2 Counting efficiencies of Ra and Ra
226 228
7.2.1 Preparation of Ra and Ra standard sources
Prepare two blank samples, consisting of barium sulfate precipitates in laboratory water, by the same
method as in 7.1.1.
Spike the first blank sample with the Ra standard solution (5.1.12).
Spike the second blank sample with the Ra standard solution (5.1.12).
Count each spiked sample a sufficient number of times to provide a reasonable data set for counting
efficiencies’ calculations.
NOTE Spiking of the samples after preparation eliminates the chemical recovery variable.
7.2.2 Determination of counting efficiencies
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Calculate the counting efficiencies of Ra and Ra (see Annex C) using Formulae (1) and (2):
s
n
226Ra
ε = (1)
226Ra
−×λ t
226Ra sR−226 a
Am××e
226Ra sR−226 a
6 © ISO 2020 – All rights reserved

ISO 22908:2020(E)
s
n
228Ra
ε = (2)
228Ra
−×λ t
228Ra sR−228 a
Am××e
228Ra sR−228 a
Acceptance limits for counting efficiencies should be defined. The use of control charts according to
[11]
ISO 7870-2 is advisable for this purpose.
Verify counting efficiencies at a periodicity established by the laboratory and whenever changes in
materials (e.g. scintillation cocktail) or when maintenance operations are performed on the liquid
scintillation counter (5.2.13). A verification or a recalibration is necessary when instrument quality
control requirements (see ISO/IEC 17025:2017, 6.4.7) are not met.
7.3 Blank sample measurement
Perform blank measurements at a periodicity established by the laboratory (e.g. for every set of
samples) and whenever changes in materials (e.g. scintillation cocktail batch) or when maintenance
operations are made on the liquid scintillation counter (5.2.13).
Acceptance limits for blank samples should be defined on the basis of the sensitivity desired. Control
[11]
charts according to ISO 7870-2 should be used for this purpose.
It is recommended that blank samples be counted for the same period of time as the test portions.
8 Procedure
8.1 General
Standard laboratory equipment (5.2.1) is required to carry out the procedure. Prior to the start of the
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analysis of Ra and Ra in the water sample, it is recommended to determine the calcium and barium
contents of the test sample using an elemental analysis technique (5.2.12) (for example, AAS, ICP-OES
or ICP-MS), since the volume of EDTA solution (5.1.9) required at the first barium sulfate precipitate
dissolution step (8.3 step 1) depends on the calcium and barium contents in the test sample.
If the barium concentration is higher than 100 mg/kg, it is recommended to reduce the volume of the
test sample to be analysed so that the total content of barium in the sample does not exceed 50 mg.
8.2 Separation of radium by precipitation
Acidify 500 ml of test sample in a glass beaker (5.2.9) to approximately pH 2 using drops of hydrochloric
acid solution (5.1.5).
Add 2 ml of lead carrier solution (5.1.2) and 2 ml of barium carrier solution (5.1.3) to the acidified
test sample. In case that the total content of barium in the sample solution is 50 mg or higher, it is not
necessary to add the barium carrier solution to the acidified test sample.
Add 4 ml of sulfuric acid solution (5.1.6) using a precision pipette (5.2.11) and 5 g of ammonium sulfate
(5.1.10) accurately weighed using an analytical balance (5.2.2).
Stir the solution (5.2.3) to ensure that all solids are dissolved, allow the precipitate to form and then let
the precipitate settle.
Decant the supernatant without disturbing the precipitate, leaving less than 30 ml of liquid in the
glassware.
Quantitatively transfer the precipitate and the limited amount of liquid to a 50 ml HDPE or PP centrifuge
tube (5.2.10) rinsing the beaker with laboratory water (5.1.1) to avoid loss of precipitate.
Centrifuge the solution for 5 min at 3 500 r/min (5.2.4).
Decant the excess supernatant carefully without disturbing the precipitate.
ISO 22908:2020(E)
8.3 Purification of radium
Dissolve the precipitate in 10 ml of hot 0,25 mol/l EDTA solution (5.1.9) and 3 ml of ammonia solution
(5.1.7) using precision pipettes (5.2.11). The volume of EDTA solution is changeable, depending on
total contents of calcium and barium in the test sample, and is given in Table C.2. Carefully agitate the
solution to dissolve the precipitate.
Add 5 ml of 100 g/kg ammonium sulfate solution (5.1.10) using a precision pipette (5.2.11) and adjust
the pH to 4,2 to 4,5 (5.2.5) using the glacial acetic acid solution (5.1.8). As the pH is lowered, the
precipitate should begin to re-form.
Warm up the solution in the HDPE or PP centrifuge tube (5.2.10) in a water bath at 80 °C for 2 min
(5.2.6), cool it with cold tap water, then centrifuge for 5 min at 3 500 r/min (5.2.4). The resulting
precipitate is purified barium (radium) sulfate precipitate. Discard the supernatant.
Dissolve the precipitate in 10 ml of hot 0,25 mol/l EDTA solution (5.1.9) and agitate the solution carefully
to dissolve the precipitate into solution. This may require the use of a vortex mixer (5.2.7). The volume
of EDTA solution is changeable, depending on total content of barium in the test sample, and is given in
Table C.3.
Add 3 ml of 100 g/kg ammonium sulfate solution (5.1.10) to the solution using a precision pipette
(5.2.11) and adjust the pH to 4,2 to 4,5 (5.2.5) using the glacial acetic acid solution (5.1.8). The precipitate
should begin to re-form. Separate the precipitate by centrifugation for 5 min at 3 500 r/min (5.2.4). The
precipitate shall not be left overnight and shall not be allowed to dry. The source shall be prepared a
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