EN ISO 19361:2020

SLOVENSKI STANDARD
01-maj-2020
Merjenje radioaktivnosti - Ugotavljanje aktivnosti oddajnikov beta - Preskusna
metoda s tekočinskim scintilacijskim štetjem (ISO 19361:2017)
Measurement of radioactivity - Determination of beta emitters activities - Test method
using liquid scintillation counting (ISO 19361:2017)
Nachweis der Radioaktivität - Bestimmung der Aktivität von Betastrahlern - Verfahren mit
Flüssigszintillationszählung (ISO 19361:2017)
Mesurage de la radioactivité - Détermination de l'activité des radionucléides émetteurs
bêta - Méthode d'essai par comptage des scintillations en milieu liquide (ISO
19361:2017)
Ta slovenski standard je istoveten z: EN ISO 19361:2020
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
February 2020
EUROPÄISCHE NORM
ICS 17.240
English Version
Measurement of radioactivity - Determination of beta
emitters activities - Test method using liquid scintillation
counting (ISO 19361:2017)
Mesurage de la radioactivité - Détermination de Nachweis der Radioaktivität - Bestimmung der
l'activité des radionucléides émetteurs bêta - Méthode Aktivität von Betastrahlern - Verfahren mit
d'essai par comptage des scintillations en milieu Flüssigszintillationszählung (ISO 19361:2017)
liquide (ISO 19361:2017)
This European Standard was approved by CEN on 7 January 2020.

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 19361:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
The text of ISO 19361:2017 has been prepared by Technical Committee ISO/TC 85 "Nuclear energy,
nuclear technologies, and radiological protection” of the International Organization for Standardization
(ISO) and has been taken over as EN ISO 19361:2020 by 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 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 19361:2017 has been approved by CEN as EN ISO 19361:2020 without any modification.

INTERNATIONAL ISO
STANDARD 19361
First edition
2017-08
Measurement of radioactivity —
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 19361:2017(E)
©
ISO 2017
ISO 19361:2017(E)
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

ISO 19361:2017(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normatives references . 1
3 Terms and definitions . 1
4 Symbols, abbreviations and units . 2
5 Principle . 2
6 Reagents and equipment . 3
6.1 Reagents. 3
6.1.1 Blank material . 3
6.1.2 Calibration source solutions . 3
6.1.3 Scintillation solution. 4
6.1.4 Quenching agent. 4
6.2 Equipment . 4
6.2.1 General. 4
6.2.2 Liquid scintillation counter . 4
6.2.3 Counting vials . 5
7 Sampling and samples . 5
7.1 Sampling . 5
7.2 Sample storage . 5
8 Procedure. 5
8.1 Determination of background . 5
8.2 Determination of detection 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 . 7
8.6.1 Control and calibration. 7
8.6.2 Measurement conditions . 7
8.6.3 Interference control . 8
9 Expression of results . 9
9.1 General . 9
9.2 Calculation of activity concentration, without preparation . 9
9.3 Decision threshold, without preparation .10
9.4 Detection limit, without preparation .10
9.5 Confidence interval limits, without preparation .10
9.6 Calculations using the activity per unit of mass, without preparation .11
10 Test report .11
Annex A (informative) Internal standard method .12
Annex B (informative) TDCR Liquid Scintillation Counting .14
Annex C (informative) Cerenkov measurement with LSC and TDCR counter .17
Bibliography .19
ISO 19361:2017(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: w w w . i s o .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.
iv © ISO 2017 – All rights reserved

ISO 19361:2017(E)
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 radiation exposures that are only a small fraction of the global
average level of natural exposure. The medical use of radiation is the largest and a growing man-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 for astronauts. The average level of occupational exposures is generally
[13]
below the global 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: (1) improve the understanding of global levels and
temporal trends of public and worker exposure; (2) to evaluate the components of exposure so as to
provide a measure of their relative importance, and; (3) to identify emerging issues that may warrant
more attention and study. While doses to workers are mostly directly measured, doses to the public are
usually assessed by indirect methods using radioactivity measurements performed on various sources:
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 need 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, 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 sample. The specific standards cover test methods for:
40 3 14
— Naturally-occurring radionuclides (including K, H, C and those originating from the thorium
226 228 234 238 210
and 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);
— Human-made radionuclides, such as transuranium elements (americium, plutonium, neptunium,
3 14 90
and curium), H, C, Sr and gamma emitting radionuclides found in waste, liquid and gaseous
ISO 19361:2017(E)
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
3 14
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 © ISO 2017 – All rights reserved

INTERNATIONAL STANDARD ISO 19361:2017(E)
Measurement of radioactivity — Determination of beta
emitters activities — Test method using liquid scintillation
counting
1 Scope
This document applies to liquid scintillation counters and requires the preparation of a scintillation
source 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).
This document describes the conditions for measuring the activity of beta emitter radionuclides by
[14][15]
liquid scintillation counting .
The choice of the test method using liquid scintillation counting involves the consideration of the potential
presence of other beta 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
a few 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
[2][3][4][5][6][7][8][9]
using liquid scintillation .
2 Normatives 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 11929, Determination of the characteristic limits (decision threshold, detection limit and limits of the
confidence interval) for measurements of ionizing radiation — Fundamentals and application
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
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
3 Terms and definitions
No terms and definitions are listed in this document.
ISO 19361:2017(E)
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at http:// www .electropedia .org/
— ISO Online browsing platform: available at https:// www .iso .org/ obp
4 Symbols, abbreviations and units
[10]
For the purposes of this document, the symbols and abbreviations defined in ISO 80000-10 ,
[11] [12]
ISO/IEC Guide 98-3 , ISO/IEC Guide 99 and the following apply.
β Maximum energy for the beta emission, in keV
max
V Volume of test portion, in litre
m Mass of test portion, in kilogram
ρ Density of the sample, in kilogram per litre
ε Preparation efficiency
p
a Activity per unit of mass, in becquerel per kilogram
c Activity concentration, in becquerel per litre
A
A Activity of the calibration source, in becquerel
t Background counting time, in second
t Portion counting time, in second
g
t Calibration counting time, in second
s
r Background count rate, per second
r Portion count rate, per second
g
r Calibration count rate, per second
s
ε Detection efficiency
ε Quenched efficiency
q
f Quench factor
q
uc Standard uncertainty associated with the measurement result; in becquerel per litre
()
A
U
Expanded uncertainty, calculated by U = k ⋅ uc with k = 1, 2,…, in becquerel per litre
()
A
*
Decision threshold, in becquerel per litre
c
A
#
Detection limit, in becquerel per litre
c
A
< >
Lower and upper limits of the confidence interval, in becquerel per litre
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). Electrons emitted from beta disintegration
transfer their energy to the scintillation cocktail molecules that are excited by this process before
returning to their ground state by emitting photons that are detected by photoelectron multiplier tubes
(phototubes).
The electronic pulses emitted by the phototubes are amplified. The peak pulse amplitude is
converted to a digital value by an analogue-to-digital convertor (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
detection efficiency, taking account of the quench correction. The requirements of the specific test
2 © ISO 2017 – All rights reserved

ISO 19361:2017(E)
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
[16][17]
curve. An 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, the blank portion 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.
For example, a water sample with a low tritium and carbon 14 activity concentration can be obtained
from (deep) subterranean water kept in a well-sealed borosilicate glass bottle in the dark at a controlled
temperature (see ISO 5667-3). When the volume of blank water is sufficiently large (e.g. 10 l to 20 l)
and well-sealed, tritium and carbon 14 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 (for example 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 made up (t = 0).
ISO 19361:2017(E)
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 solution
The scintillation cocktail is chosen according to the characteristics of the sample to be analysed and
[18][19]
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.
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.
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, an LSC-counter with three photomultipliers and appropriate
[20][21]
software may enable the activity to be determined directly (see Annex B).
For low activity measurements, a counter with low background photomultipliers, electronic equipment
with the option of background correction and suitable shielding is recommended.
4 © ISO 2017 – All rights reserved

ISO 19361:2017(E)
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 low level of K, exhibit a lower background than ‘normal’ glass vials;
— for the determination of very low concentration of low energy beta emitters (for example, tritium),
the use of polytetrafluoroethylene vials (PTFE) or polyethylene vials with an inner layer of PTFE
on 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.
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 flask 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 flasks.
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.
ISO 19361:2017(E)
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 detection 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.
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 carbon 14 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;
— 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 similar quantity of standardized solution 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;
— a reference solution is added until the desired test portion is obtained;
— the scintillation cocktail is then added in order to obtain the desired proportions;
— 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.
6 © ISO 2017 – All rights reserved

ISO 19361:2017(E)
The quench curve relating ε ⋅ f with the quenching is used to determine f :
q q
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
p
be 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 shall be written on the top of the vial stopper. 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 (e.g. after 12 h).
In order to reduce photoluminescence effects, it is recommended that the above mentioned operations
should take place in dimmed light, preferably light from an incandescent source or UV-free LED or red
light. Direct sunlight or fluorescent light should be avoided.
8.6 Counting procedure
8.6.1 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
[1]
compliance with ISO 7870-2 . Usually, these references are sealed, unquenched scintillation sources:
blank, tritium and carbon 14.
The measurement of the blank sample is performed before each analysis or each series of sample
measurement in representative conditions of each type of measurement (see Clause 5).
8.6.2 Measurement conditions
The counting room used shall be suitable for the measurement equipment and to the activity levels of
the samples.
The measurement conditions (measurement time, blank sample, number of cycles or repetitions) are
defined according to the uncertainty and detection limit to be achieved.
The measurement is performed using an energy channel A that is between the detector noise
threshold and the β of the radionuclide to be measured. It is recommended to choose the width of
max
the energy window for the counting of the radionuclide to be measured in order to optimize the figure
 


ε

of merit .



r 

 
ISO 19361:2017(E)
For measurement of low activities, it is recommended to fractionate the counting as cycles: all test
samples are counted once, then the counting starts for the second cycle, etc.
These fractionations of the counting time allow the detection of random or transitory interfering
effects (luminescence, static electricity) that are not auto-corrected by the measurement equipment. It
also allows taking into account any perturbations, intermittent or cyclic (night and day alternation for
example) associated with the measurement equipment environment.
For one cycle counting, it is recommended to arrange the counting as repetitions in order to verify the
statistical distribution of counting data. The first test sample is counted several times in a row (number
of repetitions), then the second test sample
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