EN ISO 19361:2025

SLOVENSKI STANDARD
01-september-2025
Merjenje radioaktivnosti - Ugotavljanje aktivnosti oddajnikov beta - Preskusna
metoda s tekočinskim scintilacijskim štetjem (ISO 19361:2025)
Measurement of radioactivity - Determination of beta emitters activities -Test method
using liquid scintillation counting (ISO 19361:2025)
Mesurage de la radioactivité - Détermination de l'activité des radionucléides émetteurs
bêta - Méthode d'essai par comptage des scintillations en milieu liquide (ISO
19361:2025)
Ta slovenski standard je istoveten z: EN ISO 19361:2025
ICS:
17.240 Merjenje sevanja Radiation measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 19361
EUROPEAN STANDARD
NORME EUROPÉENNE
July 2025
EUROPÄISCHE NORM
ICS 17.240 Supersedes EN ISO 19361:2020
English Version
Measurement of radioactivity - Determination of beta
emitters activities -Test method using liquid scintillation
counting (ISO 19361:2025)
Mesurage de la radioactivité - Détermination de
l'activité des radionucléides émetteurs bêta - Méthode
d'essai par comptage des scintillations en milieu
liquide (ISO 19361:2025)
This European Standard was approved by CEN on 21 July 2025.

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, Türkiye 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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 19361:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 19361:2025) has been prepared by Technical Committee ISO/TC 85 "Nuclear
energy, nuclear technologies, and radiological protection " in collaboration with Technical Committee
CEN/TC 430 “Nuclear energy, nuclear technologies, and radiological protection” the secretariat of
which is held by AFNOR.
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 January 2026, and conflicting national standards shall
be withdrawn at the latest by January 2026.
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 19361:2020.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
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, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 19361:2025 has been approved by CEN as EN ISO 19361:2025 without any modification.

International
Standard
ISO 19361
Second edition
Measurement of radioactivity —
2025-07
Determination of beta emitters
activities — Test method using
liquid scintillation counting
Mesurage de la radioactivité — Détermination de l’activité des
radionucléides émetteurs bêta — Méthode d’essai par comptage
des scintillations en milieu liquide
Reference number
ISO 19361:2025(en) © ISO 2025
ISO 19361:2025(en)
© ISO 2025
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
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
ISO 19361:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions . 2
4 Symbols . 2
5 Principle . 3
6 Reagents and equipment . 3
6.1 Reagents .3
6.1.1 Blank material .3
6.1.2 Calibration source solutions .4
6.1.3 Scintillation cocktail .4
6.1.4 Quenching agent .4
6.2 Equipment .5
6.2.1 General .5
6.2.2 Liquid scintillation counter .5
6.2.3 Counting vials .5
7 Sampling and samples . . 5
7.1 Sampling .5
7.2 Sample storage .6
8 Procedure . 6
8.1 Determination of background .6
8.2 Determination of counting efficiency .6
8.3 Quench correction .6
8.4 Sample preparation .7
8.5 Preparation of the scintillation sources to be measured .7
8.6 Counting procedure .8
8.6.1 Control and calibration .8
8.6.2 Measurement conditions .8
8.6.3 Interference control . .8
9 Expression of results . 9
9.1 General .9
9.2 Calculation of activity concentration, without sample treatment prior to measurement .9
9.3 Decision threshold, without sample treatment prior to measurement .10
9.4 Detection limit, without sample treatment prior to measurement .10
9.5 Limit of coverage interval . .11
9.5.1 Limits of the probabilistically symmetric coverage interval .11
9.5.2 Limits of the shortest coverage interval .11
9.6 Calculations using the activity per unit of mass, without sample treatment prior to
measurement . 12
10 Test report .12
Annex A (informative) Internal standard method .13
Annex B (informative) TDCR liquid scintillation counting .15
Annex C (informative) Cerenkov measurement with liquid scintillation and TDCR counter .18
Bibliography .21

iii
ISO 19361:2025(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee
has been established has the right to be represented on that committee. International organizations,
governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely
with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies, and
radiological protection, Subcommittee SC 2, Radiological protection, in collaboration with the European
Committee for Standardization (CEN) Technical Committee CEN/TC 430, Nuclear energy, nuclear technologies,
and radiological protection, in accordance with the Agreement on technical cooperation between ISO and
CEN (Vienna Agreement).
This second edition cancels and replaces the first edition (ISO 19361:2017), which has been technically
revised.
The main changes are as follows:
— those driven by the ISO 11929 series evolution for expressing results.
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 19361:2025(en)
Introduction
Everyone is exposed to natural radiation. The natural sources of radiation are cosmic rays and naturally
occurring radioactive substances which exist in the earth and within the human body. Human activities
involving the use of radiation and radioactive substances add to the radiation exposure from this natural
exposure. Some of those activities, such as the mining and use of ores containing naturally-occurring
radioactive materials (NORM) and the production of energy by burning coal that contains such substances,
simply enhance the exposure from natural radiation sources. Nuclear power plants and other nuclear
installations use radioactive materials and produce radioactive effluent and waste during operation and on
their decommissioning. The use of radioactive materials in industry, agriculture and research is expanding
around the globe.
All these human activities give rise to an average exposure to radiation that represents only a small fraction
of the global average level of exposure, taking into account all contributions (natural, medical, radon, etc.).
The medical use of radiation is the largest and a growing human-made source of radiation exposure in
developed countries. It includes diagnostic radiology, radiotherapy, nuclear medicine and interventional
radiology.
Radiation exposure also occurs as a result of occupational activities. It is incurred by workers in industry,
medicine and research using radiation or radioactive substances, as well as by passengers and crew during
air travel and by astronauts. The average level of occupational exposures is generally similar to the global
[1]
average level of natural radiation exposure .
As uses of radiation increase, so do the potential health risk and the public's concerns. Thus, all these
exposures are regularly assessed in order to
a) improve the understanding of global levels and temporal trends of public and worker exposure,
b) evaluate the components of exposure so as to provide a measure of their relative importance, and
c) identify emerging issues that may warrant more attention and study.
While doses to workers are mostly directly assessed, doses to the public are usually assessed by indirect
methods using radioactivity measurements performed on waste, effluent and/or environmental samples.
To ensure that the data obtained from radioactivity monitoring programs support their intended use,
it is essential that the stakeholders (for example, nuclear site operators, regulatory and local authorities)
agree on appropriate methods and procedures for obtaining representative samples and then handling,
storing, preparing and measuring the test samples. An assessment of the overall measurement uncertainty
needs also to be carried out systematically. As reliable, comparable and ‘fit for purpose’ data are an
essential requirement for any public health decision based on radioactivity measurements, international
standards of tested and validated radionuclide test methods are an important tool for the production of
such measurement results. The application of standards serves also to guarantee comparability over time
of the test results and between different testing laboratories. Laboratories apply them to demonstrate their
technical qualifications and to successfully complete proficiency tests during interlaboratory comparison,
two prerequisites for obtaining national accreditation. Today, over a hundred international standards,
prepared by Technical Committees of the International Standardization Organization (ISO), including
those produced by ISO/TC 85, and the International Electrotechnical Commission (IEC), are available for
application by testing laboratories to measure the main radionuclides.
Generic standards help testing laboratories to manage the measurement process by setting out the general
requirements and methods to calibrate and validate techniques. These standards underpin specific
standards which describe the test methods to be performed by staff, for example, for different types of
samples. The specific standards cover test methods for:
40 3 14
— Naturally-occurring 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, Pb) which can be found in materials from
natural sources 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);

v
ISO 19361:2025(en)
— Anthropogenic radionuclides, such as transuranium elements (americium, plutonium, neptunium, and
3 14 90
curium), H, C, Sr and gamma emitting radionuclides found in waste, liquid and gaseous effluent, in
environmental matrices (water, air, soil, biota) and food and feed as a result of authorized releases into
the environment and of fallout resulting from the explosion in the atmosphere of nuclear devices and
accidents, such as those that occurred in Chernobyl and Fukushima.
Many of these radionuclides are beta emitters that can be measured by liquid scintillation counting,
following appropriate sample preparation.
A generic international standard on liquid scintillation counting is justified for test laboratories carrying
out beta emitter measurements in fulfilment of national authority requirements. For example, testing
laboratories need to obtain a specific accreditation for radionuclide measurement for the monitoring
of drinking water, food, the environment or the discharges, as well as for biological samples for medical
purpose.
This document describes (after appropriate sampling, sample handling and test sample preparation) the
generic requirements to quantify the activity concentration of beta emitters using liquid scintillation
counting. In the absence of a specific pre-treatment of the test sample (such as distillation for H
measurement, or after benzene synthesis for C measurement), this document is to be used as a screening
method unless the interference of beta emitters, others than those to be quantified, is considered negligible
in the test portion.
This document is one of a set of generic International Standards on measurement of radioactivity.

vi
International Standard ISO 19361:2025(en)
Measurement of radioactivity — Determination of beta
emitters activities — Test method using liquid scintillation
counting
1 Scope
This document applies to the determination of beta emitters activity concentration using liquid scintillation
counting. The method requires the preparation of a scintillation source, which is obtained by mixing the test
sample and a scintillation cocktail. The test sample can be liquid (aqueous or organic), or solid (particles or
filter or planchet).
NOTE Planchet are samples, described in 8.5, out of solid material e.g. small metal, plastic or glass pans or support
material made of these materials
This document describes the conditions for measuring the activity concentration of beta emitter
[2]
radionuclides by liquid scintillation counting .
The choice of the test method using liquid scintillation counting involves the consideration of the potential
presence of other beta-, alpha- and gamma emitter radionuclides in the test sample. In this case, a specific
sample treatment by separation or extraction is implemented to isolate the radionuclide of interest in order to
avoid any interference with other beta-, alpha- and gamma-emitting radionuclides during the counting phase.
This document is applicable to all types of liquid samples having an activity concentration ranging from
−1 6 −1
about 1 Bq·l to 10 Bq·l . For a liquid test sample, it is possible to dilute liquid test samples in order to
obtain a solution having an activity compatible with the measuring instrument. For solid samples, the
activity of the prepared scintillation source shall be compatible with the measuring instrument.
The measurement range is related to the test method used: nature of test portion, preparation of the
scintillator - test portion mixture, measuring assembly as well as to the presence of the co-existing activities
due to interfering radionuclides.
3 14
Test portion preparations (such as distillation for H measurement, or benzene synthesis for C
measurement, etc.) are outside the scope of this document and are described in specific test methods using
[3][[4][5][6][7][8][9][10]
liquid scintillation .
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 5667-1, Water quality — Sampling — Part 1: Guidance on the design of sampling programmes and sampling
techniques
ISO 5667-3, Water quality — Sampling — Part 3: Preservation and handling of water samples
ISO 80000-10, Quantities and units — Part 10: Atomic and nuclear physics
ISO 18589-2, Measurement of radioactivity in the environment — Soil — Part 2: Guidance for the selection of
the sampling strategy, sampling and pre-treatment of samples
ISO/IEC Guide 98-3, Uncertainty of measurement — Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO 19361:2025(en)
ISO/IEC Guide 99, International vocabulary of metrology — Basic and general concepts and associated terms (VIM)
3 Terms, definitions
For the purposes of this document, the following term and definition 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/
3.1
quench
anything that interferes with the scintillation process and prevents light from reaching the PMT, results in a
loss in the number of recorded counts and in the apparent energy
Note 1 to entry: Physical quench occurs when the radioisotope is physically separated from the solution in which the
scintillator is dissolved.
Note 2 to entry: Chemical quench occurs when the energy of the beta particle is absorbed by compounds that will not
(or with too low efficiency) re-emit the energy during the transfer to the solvent molecules.
Note 3 to entry: Colour quench occurs when the emitted light is absorbed by colour in the sample.
4 Symbols
For the purposes of this document, the symbols and abbreviations defined in ISO 80000-10,
ISO/IEC Guide 98-3, ISO/IEC Guide 99 and the following apply.
β Maximum energy for the beta emission keV
max
V Volume of test portion l
m Mass of test portion kg
-1
ρ Density of the sample kg∙l
ε Preparation efficiency
p
-1
a Activity per unit of mass Bq∙kg
-1
c Activity concentration Bq∙l
A
A Activity of the calibration source Bq
t Background counting time s
t Portion counting time s
g
t Calibration counting time s
s
-1
r Background count rate s
-1
r Portion count rate s
g
-1
r Calibration count rate s
s
ε Counting efficiency
ε Quenched efficiency
q
f Quench factor
q
-1
uc() Standard uncertainty associated with the measurement result Bq∙l
A
-1
U Expanded uncertainty, calculated by U = k ⋅ uc with k = 1, 2,…
() Bq∙l
A
ISO 19361:2025(en)
*
-1
Decision threshold Bq∙l
c
A
# -1
Detection limit Bq∙l
c
A
< >
-1
Lower and upper limits of the confidence interval Bq∙l
c , c
A A
5 Principle
The aqueous, organic or particles portion is mixed with the scintillation cocktail in a counting vial to obtain
a homogeneous medium (scintillation source). Beta particles transfer their energy to the scintillation
cocktail molecules that are excited. The excited scintillation cocktail molecules return to their ground state
by emitting photons that are detected by photomultiplier tubes (phototubes).
The electronic pulses produced by the phototubes are amplified. At the next step; a digital number that is
proportional to the amplitude of the pulse is derived by an analogue-to-digital converter (ADC) and the pulse
height stored using a multichannel analyser (MCA). The pulses are analysed (in order to remove random
events) by the electronic systems and the data analysis software. The count rate of these photons allows the
determination of the activity in the test portion, after correcting for the background count rate and counting
efficiency, taking account of the quench correction. The requirements of the specific test method for specific
beta emitting radionuclides, including test portion preparation and scintillation source preparation, shall
be determined according to the intended use of the measurement results and the associated data quality
objectives.
In order to determine the background count rate, a blank portion shall be prepared in the same way as the
test portion.
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;
— same preparation conditions, minimizing photoluminescence and static electricity effects;
In addition, the quench indicating parameter should be within the range of the quench calibration curve. An
[11][12]
alternative method using the Cerenkov effect is treated in Annex C.
6 Reagents and equipment
Use only reagents of recognized analytical grade.
6.1 Reagents
6.1.1 Blank material
Blank material is used to prepare the blank portion. For direct counting of test portion, it shall be as free as
possible of chemical impurities to avoid quenching, and with radioactive impurities negligible in comparison
with the test portion activities to be measured.
If some preparation is required for the test portion, a blank portion representative of the preparation shall
be prepared with a reference material of the lowest activity available.
This blank sample shall be kept physically remote from any radioactive material to avoid cross-
contamination.
ISO 19361:2025(en)
3 14
For example, a water sample with a low H and C activity concentration can be obtained from (deep)
subterranean water kept in a well-sealed borosilicate glass bottle in the dark at a controlled temperature.
3 14
When the volume of blank water is sufficiently large (e.g. 10 l to 20 l) and well-sealed, H and C activity
concentrations remain stable for years, although it is advisable to determine these activity concentrations at
predetermined intervals (e.g. every year).
6.1.2 Calibration source solutions
To avoid cross-contamination, preparation of samples and calibration source solution shall be segregated.
The standardized solution used to prepare the calibration source solution shall be provided with a
calibration certificate confirming traceability to a national or international standard of radioactivity.
Weigh and pour into a weighed volumetric flask (e.g. 100 ml) the required quantity of a standardized
solution of the radionuclide to be measured, so that the activity concentration generates sufficient counts
to reach the required measurement uncertainty after dilution with the blank solution and thorough mixing.
Calculate the activity concentrations of the resulting calibration source solution (A). Note the date at which
the standard solution was prepared (t = 0).
The radionuclide activity concentration of the calibration source solution at time t at which the samples are
measured shall be corrected for radioactive decay.
6.1.3 Scintillation cocktail
The scintillation cocktail is chosen according to the characteristics of the sample to be analysed and
[13][14]
according to the properties of the detection equipment .
For the measurement of usual environmental and drinking water sample or for test sample prepared as an
aqueous solution, it is recommended to use a hydrophilic scintillation cocktail.
For the direct measurement of particles in suspension, it is recommended to use a scintillation cocktail that
leads to a gel type mixture.
In all cases, the characteristics of the scintillation cocktail when mixed with the sample shall result in a
scintillation source with the form of a homogeneous and stable medium.
It is recommended to:
— store all samples in the dark and, particularly just before use, avoiding exposure to direct sunlight or
fluorescent light in order to prevent interfering luminescence;
— comply with storage conditions specified by the scintillation cocktail supplier.
A scintillation cocktail that does not contain hazardous chemicals (as defined by the local jurisdiction)
should be used when possible.
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.
6.1.4 Quenching agent
Water, as well as dissolved oxygen, is a quenching agent for the scintillation cocktail.
Examples of chemical quenching agents include acetone, organochloride compounds, nitromethane, etc.
Some quenching agents are dangerous or toxic and shall be handled and disposed properly.

ISO 19361:2025(en)
6.2 Equipment
6.2.1 General
Laboratory equipment, such as pipettes and balances, shall be employed that enables the expected/agreed
data quality objectives to be achieved, including 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.
6.2.2 Liquid scintillation counter
Liquid scintillation counter with an automatic sample transfer is preferable. Operation at constant
temperature is recommended following the manufacturer's instructions.
The generic 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.
It is recommended to use a liquid scintillation counter using an external source, so that the level of quench
can be determined. Otherwise, a liquid scintillation counter with three photomultipliers and appropriate
[15][16]
software may enable the activity to be determined directly (see Annex B).
For low activity measurements, a counter with low background photomultipliers, a refrigerated counting
chamber, electronic equipment with the option of background correction and suitable shielding is
recommended.
6.2.3 Counting vials
Different types of scintillation vials exist, manufactured using a large 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 scintillation source.
Other types of vials exist:
— glass vials with a reduced level of K, exhibit a lower background than ‘normal’ glass vials;
— for the determination of a reduced concentration of low energy beta emitters (e.g. tritium), the use of
polytetrafluoroethylene vials (PTFE) or polyethylene vials with an inner layer of PTFE on the inside
vial wall is 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 vials are 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 use.
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.
7 Sampling and samples
7.1 Sampling
It is important that the laboratory receives a representative sample, unmodified during the transport or
storage and in an undamaged container.

ISO 19361:2025(en)
For example, for water and soil, conditions of sampling shall comply with ISO 5667-1 and ISO 18589-2
respectively.
If carbonated species are to be measured, water sample shall not be acidified in order to avoid changing the
equilibrium of carbonated species.
For water, it is recommended to use a glass container and to fill it to the maximum, to minimize tritium
exchange with the atmospheric moisture. For low level activity measurements, it is important to avoid any
contact between sample and atmosphere during the sampling.
7.2 Sample storage
If storage of samples is required, the sample shall be stored to avoid oxidation, fermentation or any
modification of its properties.
For water, if storage is required, the sample shall be stored in accordance with ISO 5667-3. If the storage
duration exceeds that specified in ISO 5667-3, it is advisable to store the samples in glass containers.
8 Procedure
8.1 Determination of background
In order to determine the background count rate, a blank sample is prepared in the same way as the test sample.
For aqueous test sample, the blank sample is prepared using a reference water of the lowest activity
available, also sometimes called “dead water”. For other matrices, the blank solution is prepared using a
reference material, as close as possible to the matrix to be measured, of the lowest activity available.
8.2 Determination of counting efficiency
In order to determine the detection efficiencies, it is necessary to measure a sample having a known activity
under conditions that are identical to those used for the sample. This sample shall be a mixture of certified
radioactive source (standardized solution) or a dilution of this mixture produced with the prepared
reference material (6.1.1).
8.3 Quench correction
The quench correction shall be considered, as mixing the organic liquid scintillation cocktail with the sample
test portion can affect the emission properties of the cocktail.
If the quenching is the same for the blank sample vial, the test sample vial and the calibration source vial, the
counting efficiency can be determined without requiring a quench correction.
Alternatively, an internal standard method can be used (see Annex A).
If chemical quenching affects the measurement results, it is recommended to determine a quench curve. It is
important to choose the chemical quenching agent according to the expected type of quenching observed in
the prepared test sample. An acid quenching agent, however, shall not be used if the chemical form of the C
in the standardized solution is carbonates.
It is useful to plot a quench curve for each matrix/radionuclide. These curves are only valid for
— a given instrument,
— a given type of counting vial,
— a given type of scintillation cocktail,
— given quantities of scintillation cocktail and test portions, and

ISO 19361:2025(en)
— a given counting window.
The quench curve is obtained from a series of working standards (e.g. around 10) having variable quench of
which the matrix is similar or close to that of the samples to be measured (same scintillation cocktail, same
quantities of scintillation cocktail and test portion).
These working standards can be produced in the following manner:
a) A similar quantity of standardized solution (6.1.2) is dispensed into each vial. Its activity shall be
sufficient so that the count rate of the working standard can be determined with a known statistical
accuracy, even at high quench levels.
b) A reference solution is added until the desired test portion is obtained.
c) The scintillation cocktail is then added in order to obtain the desired proportions.
d) At least one working standard is used without adding any quenching agent. Increasing quantities of
a quenching agent, with a very low volume (e.g. less than 1 or 2 % of the total volume of the working
standard), are added to the other working standards. This gives rise to a quench similar to that of the
samples to be measured.
The quench curve relating ε ⋅ f (ε ) with the quenching is used to determine the quench factor f using
q q q
Formula (1):
ε
q
f = (1)
q
ε
This method is not applicable to colour quenched samples.
8.4 Sample preparation
The test sample is prepared to obtain a scintillation source, aqueous or organic, which contains the
radionuclide to be measured. The efficiency of the preparation, ε , (conservation of the radionuclide to be
p
analysed through the transformation of the test sample, radiochemical yield) is to be determined.
8.5 Preparation of the scintillation sources to be measured
Known quantities of the sample and scintillation cocktail shall be dispensed into the counting vial.
For liquid and particulate samples, after closing the vial, it shall be thoroughly shaken to homogenize the
mixture.
For filter and planchet samples, great care shall be used to obtain the proper counting geometry, with the
filter or planchet materials not blocking the photons from reaching the phototubes. The active surface of the
filter or planchet shall be positioned with the activity facing into the scintillation cocktail.
The vial identification
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