SIST EN ISO 13164-4:2020

Water quality - Radon-222 - Part 4: Test method using two-phase liquid scintillation counting (ISO 13164-4:2015)

ISO 13164-4:2015 describes a test method for the determination of radon-222 (222Rn) activity concentration in non-saline waters by extraction and liquid scintillation counting.
The radon-222 activity concentrations, which can be measured by this test method utilizing currently available instruments, are at least above 0,5 Bq l−1 for a 10 ml test sample and a measuring time of 1 h.
This test method can be used successfully with drinking water samples and it is the responsibility of the laboratory to ensure the validity of this test method for water samples of untested matrices.
Annex A gives indication on the necessary counting conditions to meet the required detection limits for drinking water monitoring.

Wasserbeschaffenheit - Radon-222 - Teil 4: Verfahren mittels zweistufiger Flüssigszintillationszählung (ISO 13164-4:2015)

Dieser Teil von ISO 13164 beschreibt ein Verfahren zur Bestimmung der Aktivitätskonzentration von Radon 222 (222Rn) in nicht salzhaltigen Gewässern durch Extraktion und Flüssigszintillationszählverfahren.
Die Radon 222 Aktivitätskonzentrationen, die mit diesem Verfahren unter Verwendung derzeit verfügbarer Instrumente gemessen werden können, liegen mindestens über 0,5 Bq l−1 für eine 10 ml Analysenprobe und einen Messzeitraum von 1 h.
Dieses Verfahren kann mit Trinkwasserproben erfolgreich angewendet werden, und es liegt in der Verantwortung des Labors, die Gültigkeit dieses Verfahrens für Wasserproben nicht geprüfter Matrizen sicherzustellen.
Anhang A enthält Angaben zu den erforderlichen Zählbedingungen, um die für die Trinkwasserüberwachung erforderlichen Nachweisgrenzen zu erreichen.

Qualité de l’eau - Radon 222 - Partie 4: Méthode d’essai par comptage des scintillations en Milieu liquide à deux phases (ISO 13164-4:2015)

L'ISO 13164-4:2015 spécifie une méthode d'essai permettant de déterminer l'activité volumique du radon 222 (222Ra) dans des eaux non salines par extraction et comptage des scintillations en milieu liquide.
Les valeurs d'activité volumique du radon 222 qui peuvent être mesurées par cette méthode d'essai à l'aide d'instruments actuellement disponibles, sont au moins supérieures à 0,5 Bq l−1 pour une prise d'essai de 10 ml et un temps de comptage de 1 h.
Cette méthode d'essai peut être utilisée avec succès sur des échantillons d'eau potable et il appartient au laboratoire de s'assurer de la validité de cette méthode d'essai pour des échantillons d'eau provenant de matrices non testées.
L'Annexe A donne une indication sur les conditions de comptage nécessaires pour obtenir les limites de détection requises pour la surveillance de l'eau potable.

Kakovost vode - Radon Rn-222 - 4. del: Preskusna metoda s štetjem z dvofaznim tekočinskim scintilatorjem (ISO 13164-4:2015)

General Information

• Status: Published
• Public Enquiry End Date: 01-Aug-2019
• Publication Date: 07-Apr-2020
• ICS: 13.060.60 - Examination of physical properties of water
• ICS: 17.240 - Radiation measurements
• Technical Committee: KAV - Water quality
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 31-Mar-2020
• Due Date: 05-Jun-2020
• Completion Date: 08-Apr-2020
• Ref Project: EN ISO 13164-4:2020 - Water quality - Radon-222 - Part 4: Test method using two-phase liquid scintillation counting (ISO 13164-4:2015)

Relations

• Revises: oSIST prEN ISO 13164-4:2022 - Water quality - Radon-222 - Part 4: Test method using two-phase liquid scintillation counting (ISO/DIS 13164-4:2022)
• Effective Date: 18-Jan-2023
• Revised: oSIST prEN ISO 13164-4:2022 - Water quality - Radon-222 - Part 4: Test method using two-phase liquid scintillation counting (ISO/DIS 13164-4:2022)
• Effective Date: 01-Apr-2022

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN ISO 13164-4:2020
01-maj-2020
Kakovost vode - Radon Rn-222 - 4. del: Preskusna metoda s štetjem z dvofaznim
tekočinskim scintilatorjem (ISO 13164-4:2015)

Water quality - Radon-222 - Part 4: Test method using two-phase liquid scintillation

counting (ISO 13164-4:2015)
Wasserbeschaffenheit - Radon-222 - Teil 4: Verfahren mittels zweistufiger
Flüssigszintillationszählung (ISO 13164-4:2015)

Qualité de l’eau - Radon 222 - Partie 4: Méthode d’essai par comptage des scintillations

en Milieu liquide à deux phases (ISO 13164-4:2015)
Ta slovenski standard je istoveten z: EN ISO 13164-4:2020
ICS:
13.060.60 Preiskava fizikalnih lastnosti Examination of physical
vode properties of water
17.240 Merjenje sevanja Radiation measurements
SIST EN ISO 13164-4:2020 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 13164-4:2020
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SIST EN ISO 13164-4:2020
EN ISO 13164-4
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2020
EUROPÄISCHE NORM
ICS 13.060.60; 17.240; 13.280
English Version
Water quality - Radon-222 - Part 4: Test method using
two-phase liquid scintillation counting (ISO 13164-
4:2015)

Qualité de l'eau - Radon 222 - Partie 4: Méthode d'essai Wasserbeschaffenheit - Radon-222 - Teil 4: Verfahren

par comptage des scintillations en milieu liquide à mittels zweistufiger Flüssigszintillationszählung (ISO

deux phases (ISO 13164-4:2015) 13164-4:2015)
This European Standard was approved by CEN on 6 October 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 13164-4:2020 E

worldwide for CEN national Members.
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SIST EN ISO 13164-4:2020
EN ISO 13164-4:2020 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 13164-4:2020
EN ISO 13164-4:2020 (E)
European foreword

The text of ISO 13164-4:2015 has been prepared by Technical Committee ISO/TC 147 "Water quality”

of the International Organization for Standardization (ISO) and has been taken over as EN ISO 13164-

4:2020 by 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 13164-4:2015 has been approved by CEN as EN ISO 13164-4:2020 without any

modification.
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SIST EN ISO 13164-4:2020
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SIST EN ISO 13164-4:2020
INTERNATIONAL ISO
STANDARD 13164-4
First edition
2015-06-15
Water quality — Radon-222 —
Part 4:
Test method using two-phase liquid
scintillation counting
Qualité de l’eau — Radon 222 —
Partie 4: Méthode d’essai par comptage des scintillations en milieu
liquide à deux phases
Reference number
ISO 13164-4:2015(E)
ISO 2015
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SIST EN ISO 13164-4:2020
ISO 13164-4:2015(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2015, 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. [phone]
Fax [phone]
[e-mail]
www.iso.org
ii © ISO 2015 – All rights reserved
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SIST EN ISO 13164-4:2020
ISO 13164-4:2015(E)
Contents Page

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

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

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

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

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

3.1 Terms and definitions ....................................................................................................................................................................... 1

3.2 Symbols and abbreviated terms............................................................................................................................................... 1

4 Principle ........................................................................................................................................................................................................................ 2

5 Reagents and apparatus ............................................................................................................................................................................... 2

5.1 Reagents........................................................................................................................................................................................................ 2

5.2 Apparatus .................................................................................................................................................................................................... 3

6 Sampling ........................................................................................................................................................................................................................ 3

6.1 General ........................................................................................................................................................................................................... 3

6.2 Sampling with source preparation “on site” .................................................................................................................. 3

6.3 Sampling without “on site” source preparation ......................................................................................................... 4

7 Instrument set up and calibration ..................................................................................................................................................... 4

7.1 Preparation of calibration sources ........................................................................................................................................ 4

7.2 Optimization of counting conditions ................................................................................................................................... 4

7.3 Detection efficiency............................................................................................................................................................................. 4

7.4 Blank sample preparation and measurement .............................................................................................................. 5

8 Sample preparation and measurement ........................................................................................................................................ 5

9 Expression of results ........................................................................................................................................................................................ 6

9.1 Calculation of activity per unit of mass .............................................................................................................................. 6

9.2 Standard uncertainty ......................................................................................................................................................................... 6

9.3 Decision threshold ............................................................................................................................................................................... 6

9.4 Detection limit ......................................................................................................................................................................................... 7

9.5 Confidence limits................................................................................................................................................................................... 7

9.6 Calculations using the activity concentration .............................................................................................................. 7

10 Interference control .......................................................................................................................................................................................... 8

11 Quality control ........................................................................................................................................................................................................ 8

12 Test report ................................................................................................................................................................................................................... 8

Annex A (informative) Set-up parameters and validation data ................................................................................................ 9

Bibliography .............................................................................................................................................................................................................................12

© ISO 2015 – All rights reserved iii
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SIST EN ISO 13164-4:2020
ISO 13164-4:2015(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 meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO’s adherence to the WTO principles in the Technical Barriers

to Trade (TBT), see the following URL: Foreword — Supplementary information.

The committee responsible for this document is ISO/TC 147, Water quality, Subcommittee SC 3,

Radioactivity measurements.

ISO 13164 consists of the following parts, under the general title Water quality — Radon-222:

— Part 1: General principles
— Part 2: Test method using gamma-ray spectrometry
— Part 3: Test method using emanometry
— Part 4: Test method using two-phase liquid scintillation counting
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SIST EN ISO 13164-4:2020
ISO 13164-4:2015(E)
Introduction

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

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

of natural or human-made origin, or both.

— Natural radionuclides, including potassium-40, and those originating from the thorium and uranium

decay series, in particular radium-226, radium-228, uranium-234, uranium-238, and lead-210, can

be found in water for natural reasons (e.g. desorption from the soil and wash-off by rain water) or

can be released from technological processes involving naturally occurring radioactive materials

(e.g. the mining and processing of mineral sands or phosphate fertilizer production and use).

— Human-made radionuclides such as transuranium elements (americium, plutonium, neptunium,

curium), tritium, carbon-14, strontium-90, and some gamma-emitting radionuclides can also be

found in natural waters as a result of authorized routine releases into the environment in small

quantities in the effluent discharged from nuclear fuel cycle facilities. They are also released into

the environment following their use in unsealed form in medicine or industrial applications. They

are also found in the water as a result of past fallout resulting from explosion in the atmosphere of

nuclear devices and accidents such as those that occurred in Chernobyl and Fukushima.

Drinking water can, thus, contain radionuclides at activity concentration which could present a risk to

human health. In order to assess the quality of drinking water (including mineral waters and spring

waters) with respect to its radionuclide content and to provide guidance on reducing health risks by

taking measures to decrease radionuclide activity concentrations, water resources (groundwater, river,

lake, sea, etc.) and drinking water are monitored for their radioactivity content as recommended by the

World Health Organization (WHO) and may be required by some national authorities.

Standard test methods for radon-222 activity concentrations in water samples are needed by test

laboratories carrying out such measurements in fulfilment of national authority requirements.

Laboratories may have to obtain a specific accreditation for radionuclide measurement in drinking

water samples.

The radon activity concentration in surface water is very low, usually below 1 Bq l . In groundwater, the

−1 −1 −1

activity concentration varies from 1 Bq l up to 50 Bq l in sedimentary rock aquifers, from 10 Bq l

−1 −1 −1

up to 300 Bq l in wells, and from 100 Bq l up to 1 000 Bq l in crystalline rocks. The highest activity

concentrations are normally measured in rocks with high concentration of uranium (see Reference [9]).

High variations in the activity concentrations of radon in aquifers have been observed. Even in a region

with relatively uniform rock types, some well water can exhibit radon activity concentration greatly

higher than the average value for the same region. Significant seasonal variations have also been

recorded (see ISO 13164-1:2013, Annex A).

Water can dissolve chemical substances as it passes from the soil surface to an aquifer or spring waters.

The water can pass through or remain for some time in rock, some formations of which can contain a

high concentration of natural radionuclides. Under favourable geochemical conditions, the water can

selectively dissolve some of these natural radionuclides.

Guidance on radon in drinking water supplies provided by WHO in 2008 suggests that controls should be

implemented if the radon concentration of drinking water for public water supplies exceeds 100 Bq l .

It is also recommended that any new, especially public, drinking water supply using groundwater

should be tested prior to being used for general consumption and that if the radon concentration

exceeds 100 Bq l , treatment of the water source should be undertaken to reduce the radon levels to

well below that level (see Reference [10]).

This part of ISO 13164 is one of the series dealing with the measurement of the activity concentration of

radionuclides in water samples.

The origin of radon-222 and its short-lived decay products in water and other measurement methods

are described generally in ISO 13164-1.
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SIST EN ISO 13164-4:2020
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SIST EN ISO 13164-4:2020
INTERNATIONAL STANDARD ISO 13164-4:2015(E)
Water quality — Radon-222 —
Part 4:
Test method using two-phase liquid scintillation counting

WARNING — Persons using this part of ISO 13164 should be familiar with normal laboratory

practice. This part of ISO 13164 does not purport to address all of the safety issues, if any,

associated with its use. It is the responsibility of the user to establish appropriate safety and

health practices and to ensure compliance with any national regulatory conditions.

IMPORTANT — It is absolutely essential that tests conducted in accordance with this part of

ISO 13164 be carried out by suitably qualified staff.
1 Scope
222

This part of ISO 13164 describes a test method for the determination of radon-222 ( Rn) activity

concentration in non-saline waters by extraction and liquid scintillation counting.

The radon-222 activity concentrations, which can be measured by this test method utilizing currently

available instruments, are at least above 0,5 Bq l for a 10 ml test sample and a measuring time of 1 h.

This test method can be used successfully with drinking water samples and it is the responsibility of the

laboratory to ensure the validity of this test method for water samples of untested matrices.

Annex A gives indication on the necessary counting conditions to meet the required detection limits for

drinking water monitoring.
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. 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 80000-10, Quantities and units — Part 10: Atomic and nuclear physics

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

3 Terms and definitions and symbols
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 80000-10 apply.

3.2 Symbols and abbreviated terms

For the purposes of this document, symbols and abbreviations defined in ISO 80000-10, as well as the

following symbols, apply.
a massic activity of the sample, in becquerels per gram
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SIST EN ISO 13164-4:2020
ISO 13164-4:2015(E)

a massic activity of the standard solution at the measuring time, in becquerels per gram

a* decision threshold for the total massic activity, in becquerels per gram
a detection limit for the total massic activity, in becquerels per gram
⊲ ⊳
a , a lower and upper limits of the confidence interval, in becquerels per gram
c activity concentration, in becquerels per litre
m mass of the test sample, in grams

m mass of standard solution used for the preparation of the counting standard, in grams

r blank sample count rate, in reciprocal seconds
r sample gross count rate, in reciprocal seconds

r count rate of the standard in the counting window (alpha + beta), in reciprocal seconds

t blank sample counting time, in seconds
t test sample counting time, in seconds
t calibration sample counting time, in seconds

u(a) standard uncertainty associated with the measurement result; in becquerels per gram

U expanded uncertainty, calculated using U = ku(a), with k = 2, in becquerels per gram

w coefficient equal to 1/(ε m), in reciprocal gram
ε total efficiency
ρ density, in grams per litre
4 Principle
222

Rn is extracted from aqueous solution by means of a scintillation cocktail not miscible with water

(without emulsifier) inside the scintillation vial and counted as the equilibrium with its short lived

[1] [2] [3] [4]
decay products is reached.

The aqueous sample is drawn by the mean of a gas-tight syringe from inside the water volume (i.e. well

below surface) to avoid radon losses during sampling and transferred into a scintillation vial containing

the desired amount of scintillation cocktail. For the same reason, the water sample is injected below

the cocktail surface. The vial is tightly capped, shaken and kept for 3 h preferably in the dark and at

controlled temperature. The sample is then counted by a liquid scintillation counter. Either total counts

222

(alpha + beta) or alpha only counts are considered. In these conditions Rn and its short lived progeny

218 214 214 214
( Po, Pb, Bi, and Po) are measured.
5 Reagents and apparatus
5.1 Reagents

All reagents shall be of recognized analytical grade and, except for 5.1.4, shall not contain any detectable

alpha and beta activity.
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5.1.1 Water, distilled or deionized, complying with ISO 3696, grade 3.
222

Deionized water can contain detectable amounts of Rn and short lived daughters. It is, therefore,

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

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

5.1.2 Scintillation cocktail, commercially available scintillation cocktails, not water miscible.

5.1.3 Ethanol, 95 %.
5.1.4 Radium standard solution.
226

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

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

specification.
5.2 Apparatus
5.2.1 Balance.
5.2.2 Wide-mouth glass sample bottles, volume from 500 ml to 1 l.
5.2.3 Wide-mouth Erlenmeyer flask, volume from 500 ml to 1 l.
5.2.4 Gas-tight syringe.

5.2.5 Liquid scintillation counter, preferably with thermostated counting chamber and preferably

ultra-low level counter to achieve better detection limits.
5.2.6 Polyethylene scintillation vials, PTFE coated, volume 20 ml.
5.2.7 Glass scintillation vials, low potassium glass, volume 20 ml.

NOTE PTFE coated polyethylene vials are the best choice since they prevent both the diffusion of the cocktail

into the wall of the vial, radon loss and the absorption of radon from the external environment. Glass vials exhibit

a considerably higher background due to potassium-40 content.
6 Sampling
6.1 General

Since radon is easily desorbed from water sample, care should be taken to avoid analyte losses during

the sampling.
6.2 Sampling with source preparation “on site”

Attach a plastic tube to a faucet with a proper fitting. Insert the other end of the tube in a wide-mouth

Erlenmeyer flask (5.2.3). Allow a steady water stream to get out and overflow the flask for approximately

2 min. Adjust the flux to avoid turbulence, bubbles, and empty volumes both in the tube and in the flask.

Draw the water sample aliquot with a gas-tight syringe (5.2.4) inserting the needle well below the

surface.
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6.3 Sampling without “on site” source preparation

Attach a plastic tube to a faucet with a proper fitting. Insert the other end of the tube in a wide-

mouth borosilicate bottle (5.2.2). Allow a steady water stream to flow out and overflow the bottle for

approximately 2 min. Adjust flux to avoid turbulence, bubbles, and empty volumes both in the tube and

in the bottle. Gently extract the tube and screw tightly the cap avoiding any air head space. A one-litre

bottle is generally suitable for the sampling.

The sample should be transported into laboratory and analysed possibly within 48 h. The sample should

neither be frozen nor overheated. Its preservation at temperature not higher than that of the sampled

water is recommended.
7 Instrument set up and calibration
7.1 Preparation of calibration sources
226

Transfer an accurately known amount m of the Ra standard solution (5.1.4) into a 20 ml scintillation

vial (5.2.6 or 5.2.7). Let the massic activity at the measuring time be a . Dilute with laboratory water

(5.1.1) (see ISO 3696) to the previously chosen mass (e.g. 10 g). Add the scintillation cocktail (5.1.2).

Store the sample for at least 30 days to allow the achievement of secular equilibrium.

222

A standard solution of Rn can also be used if available. In this case, it can be counted 3 h after its

preparation. Since Ra-226 is not extracted into the organic phase, its alpha emission would not affect

detection efficiency calibration for Rn-222.
7.2 Optimization of counting conditions

Both alpha + beta counting or alpha counting using alpha-beta discrimination can be used (see

manufacturer instructions).

When using alpha-beta discrimination, both alpha background and efficiency are usually lower; in

practice it is found that a much lower detection limit can be achieved.

Set the counting window so that the channels affected by photo and chemo-luminescence are excluded.

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

quenching correction is needed.
7.3 Detection efficiency

Let the counting rate be r for the counts of the calibration source in the counting window (alpha + beta).

Determine the detection efficiency:
rr−
S 0
ε = (1)
am⋅
Acceptance limits for efficiency should be defined.

NOTE ε includes both counting and extraction efficiency. Usual values are in the range of 400 % to 500 %

222 218 214 214 214

( Rn, Po, Po alpha emissions and Pb, Bi beta emissions). If using alpha only counting, a lower ε value

(≤ 300 %) is to be expected.

It is advisable to check the method linearity. The efficiency should be assessed using calibration sources

whose activities should cover the whole working range.

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

of calibration sources.
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