SIST EN ISO 11665-3:2020

Measurement of radioactivity in the environment - Air: radon-222 - Part 3: Spot measurement method of the potential alpha energy concentration of its short-lived decay products (ISO 11665-3:2020)

This document describes spot measurement methods for determining the activity concentration of short-lived radon-222 decay products in the air and for calculating the potential alpha energy concentration.
This document gives indications for performing a spot measurement of the potential alpha energy concentration, after sampling at a given place for several minutes, and the conditions of use for the measuring devices.
The measurement method described is applicable for a rapid assessment of the potential alpha energy concentration. The result obtained cannot be extrapolated to an annual estimate potential alpha energy concentration of short-lived radon-222 decay products. Thus, this type of measurement is not applicable for the assessment of annual exposure or for determining whether or not to mitigate citizen exposures to radon or radon decay products.
This measurement method is applicable to air samples with potential alpha energy concentration greater than 5 nJ/m3.
NOTE       This document does not address the potential contribution of radon-220 decay products.

Ermittlung der Radioaktivität in der Umwelt - Luft: Radon-222 - Teil 3: Punktmessverfahren der potenziellen Alpha-Energiekonzentration der kurzlebigen Radon-Folgeprodukte (ISO 11665-3:2020)

Dieses Dokument beschreibt Punktmessverfahren für die Bestimmung der Aktivitätskonzentration der kurz-lebigen 222Rn-Folgeprodukte in der Luft und zur Berechnung der potenziellen Alpha-Energiekonzen¬tration.
Dieses Dokument gibt Hinweise für die Punktmessung der potenziellen Alpha-Energiekonzentration, bei der die Probenahme während einiger Minuten an einem bestimmten Ort durchgeführt wird und zu den Bedingun-gen beim Einsatz der Messgeräte.
Dieses Messverfahren ist anwendbar für die schnelle Bestimmung der potenziellen Alpha-Energiekonzentra-tion. Das erhaltene Ergebnis kann nicht extrapoliert werden, um eine potenzielle Alpha-Energiekonzentration der kurzlebigen 222Rn-Folgeprodukte während eines Jahres abzuschätzen. Deshalb ist diese Art der Mes-sung nicht für die Bewertung der Jahresexposition einsetzbar oder zur Bestimmung, ob die Belastung der Bevölkerung durch Radon oder Radonfolgeprodukte verringert werden muss.
Dieses Messverfahren ist für Luftproben mit einer potenziellen Alpha-Energiekonzentration größer als 5 nJ m–3 anwendbar.
ANMERKUNG   220Rn-Folgeprodukte sind nicht Gegenstand dieses Dokuments.

Mesurage de la radioactivité dans l'environnement - Air: radon 222 - Partie 3: Méthode de mesure ponctuelle de l'énergie alpha potentielle volumique de ses descendants à vie courte (ISO 11665-3:2020)

Le présent document décrit les méthodes de mesure ponctuelle destinées à déterminer l'activité volumique des descendants à vie courte du radon-222 dans l'air et à calculer de l'énergie alpha potentielle volumique.
Le présent document fournit des indications pour réaliser un mesurage ponctuel de l'énergie alpha potentielle volumique avec un prélèvement effectué en un lieu donné pendant plusieurs minutes, et sur les conditions d'utilisation des dispositifs de mesure.
La méthode de mesure décrite s'applique pour une évaluation rapide de l'énergie alpha potentielle volumique. Le résultat obtenu ne peut pas être extrapolé à une estimation annuelle de l'énergie alpha potentielle volumique des descendants à vie courte du radon-222. Par conséquent, ce type de mesurage ne s'applique pas à l'évaluation de l'exposition annuelle ni à la détermination de l'opportunité de réduire ou non l'exposition des citoyens au radon ou aux descendants du radon.
Cette méthode de mesure s'applique à des échantillons d'air ayant une énergie alpha potentielle volumique supérieure à 5 nJ/m3.
NOTE       Le présent document ne couvre pas la contribution potentielle des descendants du radon-220.

Merjenje radioaktivnosti v okolju - Zrak: radon Rn-222 - 3. del: Točkovna metoda za merjenje potencialne koncentracije alfa energije njegovih kratkoživih razpadnih produktov (ISO 11665-3:2020)

General Information

• Status: Published
• Public Enquiry End Date: 17-Dec-2019
• Publication Date: 16-Feb-2020
• ICS: 13.040.99 - Other standards related to air quality
• ICS: 17.240 - Radiation measurements
• Technical Committee: I13 - Imaginarni 13
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 13-Feb-2020
• Due Date: 19-Apr-2020
• Completion Date: 17-Feb-2020
• Ref Project: EN ISO 11665-3:2020 - Measurement of radioactivity in the environment - Air: radon-222 - Part 3: Spot measurement method of the potential alpha energy concentration of its short-lived decay products (ISO 11665-3:2020)

Relations

• Replaces: SIST EN ISO 11665-3:2015 - Measurement of radioactivity in the environment - Air: radon-222 - Part 3: Spot measurement method of the potential alpha energy concentration of its short-lived decay products (ISO 11665-3:2012)
• Effective Date: 12-Feb-2020
• Revised: SIST EN ISO 11665-3:2015 - Measurement of radioactivity in the environment - Air: radon-222 - Part 3: Spot measurement method of the potential alpha energy concentration of its short-lived decay products (ISO 11665-3:2012)
• Effective Date: 13-Jun-2018

Overview

EN ISO 11665-3:2020 (Measurement of radioactivity in the environment - Air: radon-222 - Part 3) specifies a spot measurement method to determine the potential alpha energy concentration (PAEC) of short-lived radon‑222 decay products in air. It describes short-duration sampling (sampling at a given place for several minutes), measurement procedures, device-use conditions and calculation of PAEC for rapid on-site assessment. The method applies to air samples with PAEC > 5 nJ/m3 and does not address radon‑220 decay products or provide results that can be extrapolated to annual exposure or to make mitigation decisions.

Key topics and requirements

• Measurement principle: Sampling of airborne short‑lived decay products followed by alpha counting to derive PAEC (potential alpha energy concentration).
• Scope limits: Intended for rapid spot assessments only; results are not suitable for annual exposure estimates or mitigation thresholds.
• Sampling: Short-duration spot sampling (sampling for several minutes) at a fixed location; guidance on sampling objectives, installation and sampling conditions.
• Detection methods: Gross alpha counting and protocols (examples and the Thomas protocol are included in annexes).
• Equipment & calibration: Requirements for suitable sampling devices and detectors, calibration procedures and device conditions to ensure reliable spot readings.
• Data expression & quality: Calculation and reporting of PAEC, standard uncertainty, decision threshold, detection limit and confidence intervals.
• Informative annexes: Examples of counting protocols, calculation of coefficient factors and a Thomas-protocol example for gross alpha counting.

Practical applications and users

EN ISO 11665-3:2020 is especially useful for:

• Radiation protection professionals conducting rapid on-site surveys of radon decay products.
• Environmental monitoring teams performing spot checks in buildings, workplaces or research sites.
• Public health agencies and consultants needing quick assessments of short‑term PAEC levels.
• Laboratories and instrument manufacturers seeking standard test procedures, calibration and reporting formats.
• Researchers studying short-term spatial or temporal variations of radon decay products.

Note: Because the method targets rapid spot measurements only, it should be used alongside long‑term monitoring methods (other parts of the ISO 11665 series) when assessing annual exposure or planning mitigation.

Related standards

• ISO 11665 series (other parts covering radon measurement principles and long-term measurements)
• ISO 11665‑1:2019 (general information on radon)
• ISO 13164 series (radon in water) - referenced for broader radon measurement context

Keywords: EN ISO 11665-3:2020, ISO 11665-3, radon-222, radon decay products, spot measurement, potential alpha energy concentration, PAEC, radon monitoring, gross alpha counting.

Standards Content (Sample)

SLOVENSKI STANDARD
01-april-2020
Nadomešča:
SIST EN ISO 11665-3:2015
Merjenje radioaktivnosti v okolju - Zrak: radon Rn-222 - 3. del: Točkovna metoda
za merjenje potencialne koncentracije alfa energije njegovih kratkoživih razpadnih
produktov (ISO 11665-3:2020)
Measurement of radioactivity in the environment - Air: radon-222 - Part 3: Spot
measurement method of the potential alpha energy concentration of its short-lived decay
products (ISO 11665-3:2020)
Ermittlung der Radioaktivität in der Umwelt - Luft: Radon-222 - Teil 3:
Punktmessverfahren der potenziellen Alpha-Energiekonzentration der kurzlebigen
Radon-Folgeprodukte (ISO 11665-3:2020)
Mesurage de la radioactivité dans l'environnement - Air: radon 222 - Partie 3: Méthode
de mesure ponctuelle de l'énergie alpha potentielle volumique de ses descendants à vie
courte (ISO 11665-3:2020)
Ta slovenski standard je istoveten z: EN ISO 11665-3:2020
ICS:
13.040.99 Drugi standardi v zvezi s Other standards related to air
kakovostjo zraka quality
17.240 Merjenje sevanja Radiation measurements
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN ISO 11665-3
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2020
EUROPÄISCHE NORM
ICS 17.240 Supersedes EN ISO 11665-3:2015
English Version
Measurement of radioactivity in the environment - Air:
radon-222 - Part 3: Spot measurement method of the
potential alpha energy concentration of its short-lived
decay products (ISO 11665-3:2020)
Mesurage de la radioactivité dans l'environnement - Ermittlung der Radioaktivität in der Umwelt - Luft:
Air: radon 222 - Partie 3: Méthode de mesure Radon-222 - Teil 3: Punktmessverfahren der
ponctuelle de l'énergie alpha potentielle volumique de potenziellen Alpha-Energiekonzentration der
ses descendants à vie courte (ISO 11665-3:2020) kurzlebigen Radon-Folgeprodukte (ISO 11665-3:2020)
This European Standard was approved by CEN on 19 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 11665-3:2020 E
worldwide for CEN national Members.

Contents Page
European foreword . 3

European foreword
This document (EN ISO 11665-3:2020) 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 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.
This document supersedes EN ISO 11665-3:2015.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, 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 11665-3:2020 has been approved by CEN as EN ISO 11665-3:2020 without any
modification.
INTERNATIONAL ISO
STANDARD 11665-3
Second edition
2020-01
Measurement of radioactivity in the
environment — Air: radon-222 —
Part 3:
Spot measurement method of the
potential alpha energy concentration
of its short-lived decay products
Mesurage de la radioactivité dans l'environnement — Air: radon 222 —
Partie 3: Méthode de mesure ponctuelle de l'énergie alpha potentielle
volumique de ses descendants à vie courte
Reference number
ISO 11665-3:2020(E)
©
ISO 2020
ISO 11665-3:2020(E)
© ISO 2020
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Fax: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved

ISO 11665-3:2020(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and symbols . 1
3.1 Terms and definitions . 1
3.2 Symbols . 2
4 Principle of the measurement method . 3
5 Equipment . 3
6 Sampling . 4
6.1 General . 4
6.2 Sampling objective . 4
6.3 Sampling characteristics . . 4
6.4 Sampling conditions . 5
6.4.1 General. 5
6.4.2 Installation of sampling system . 5
6.4.3 Sampling duration . 5
6.4.4 Volume of air sampled . . . 5
7 Detection method . 5
8 Measurement . 5
8.1 Procedure . 5
8.2 Influence quantities . 6
8.3 Calibration . 6
9 Expression of results . 7
9.1 General . 7
9.2 Potential alpha energy concentration . 7
9.3 Standard uncertainty . 7
9.4 Decision threshold . 8
9.5 Detection limit . 9
9.6 Limits of the confidence interval . 9
10 Test report . 9
Annex A (informative) Examples of gross alpha counting protocols .11
Annex B (informative) Calculation of the coefficients k , k and k .12
218 ,j 214 ,j 214 ,j
Po Pb Bi
Annex C (informative) Measurement method using gross alpha counting according to the
Thomas protocol .16
Bibliography .19
ISO 11665-3:2020(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/ patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation 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 the following
URL: : 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.
This second edition cancels and replaces the first edition (ISO 11665-3:2012), of which it constitutes a
minor revision. The changes compared to the previous edition are as follows:
— update of the Introduction;
— update of the Bibliography.
A list of all the parts in the ISO 11665 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved

ISO 11665-3:2020(E)
Introduction
Radon isotopes 222, 219 and 220 are radioactive gases produced by the disintegration of radium isotopes
226, 223 and 224, which are decay products of uranium-238, uranium-235 and thorium-232 respectively,
and are all found in the earth's crust (see ISO 11665-1:2019, Annex A for further information). Solid
[1]
elements, also radioactive, followed by stable lead are produced by radon disintegration .
When disintegrating, radon emits alpha particles and generates solid decay products, which are also
radioactive (polonium, bismuth, lead, etc.). The potential effects on human health of radon lie in its solid
decay products rather than the gas itself. Whether or not they are attached to atmospheric aerosols,
radon decay products can be inhaled and deposited in the bronchopulmonary tree to varying depths
[2][3][4][5]
according to their size .
[6]
Radon is today considered to be the main source of human exposure to natural radiation. UNSCEAR
suggests that, at the worldwide level, radon accounts for around 52 % of global average exposure to
natural radiation. The radiological impact of isotope 222 (48 %) is far more significant than isotope
220 (4 %), while isotope 219 is considered negligible (see ISO 11665-1:2019, Annex A). For this reason,
references to radon in this document refer only to radon-222.
Radon activity concentration can vary from one to more orders of magnitude over time and space.
Exposure to radon and its decay products varies tremendously from one area to another, as it depends
on the amount of radon emitted by the soil and building materials, weather conditions, and on the
degree of containment in the areas where individuals are exposed.
As radon tends to concentrate in enclosed spaces like houses, the main part of the population exposure
is due to indoor radon. Soil gas is recognized as the most important source of residential radon through
infiltration pathways. Other sources are described in other parts of ISO 11665 and ISO 13164 series for
[7]
water .
Radon enters into buildings via diffusion mechanism caused by the all-time existing difference between
radon activity concentrations in the underlying soil and inside the building, and via convection
mechanism inconstantly generated by a difference in pressure between the air in the building and the
air contained in the underlying soil. Indoor radon activity concentration depends on radon activity
concentration in the underlying soil, the building structure, the equipment (chimney, ventilation
systems, among others), the environmental parameters of the building (temperature, pressure, etc.)
and the occupants’ lifestyle.
-3
To limit the risk to individuals, a national reference level of 100 Bq.m is recommended by the World
[5] -3
Health Organization . Wherever this is not possible, this reference level should not exceed 300 Bq·m .
This recommendation was endorsed by the European Community Member States that should establish
national reference levels for indoor radon activity concentrations. The reference levels for the annual
-3[5]
average activity concentration in air should not be higher than 300 Bq·m .
To reduce the risk to the overall population, building codes should be implemented that require radon
prevention measures in buildings under construction and radon mitigating measures in existing
buildings. Radon measurements are needed because building codes alone cannot guarantee that radon
concentrations are below the reference level.
Variations of a few nanojoules per cubic metre to several thousand nanojoules per cubic metre are
observed in the potential alpha energy concentration of short-lived radon decay products.
The potential alpha energy concentration of short-lived radon-222 decay products in the atmosphere
can be measured by spot and integrated measurement methods (see ISO 11665-1). This document deals
with spot measurement methods. A spot measurement of the potential alpha energy concentration
relates to the time when the measurement is taken and has no significance in annual exposure. This
type of measurement does not therefore apply when assessing the annual exposure.
NOTE The origin of radon-222 and its short-lived decay products in the atmospheric environment are
described generally in ISO 11665-1 together with measurement methods.
INTERNATIONAL STANDARD ISO 11665-3:2020(E)
Measurement of radioactivity in the environment — Air:
radon-222 —
Part 3:
Spot measurement method of the potential alpha energy
concentration of its short-lived decay products
1 Scope
This document describes spot measurement methods for determining the activity concentration
of short-lived radon-222 decay products in the air and for calculating the potential alpha energy
concentration.
This document gives indications for performing a spot measurement of the potential alpha energy
concentration, after sampling at a given place for several minutes, and the conditions of use for the
measuring devices.
The measurement method described is applicable for a rapid assessment of the potential alpha energy
concentration. The result obtained cannot be extrapolated to an annual estimate potential alpha energy
concentration of short-lived radon-222 decay products. Thus, this type of measurement is not applicable
for the assessment of annual exposure or for determining whether or not to mitigate citizen exposures
to radon or radon decay products.
This measurement method is applicable to air samples with potential alpha energy concentration
greater than 5 nJ/m .
NOTE This document does not address the potential contribution of radon-220 decay products.
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 11665-1, Measurement of radioactivity in the environment — Air: radon-222 — Part 1: Origins of radon
and its short-lived decay products and associated measurement methods
ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
IEC 61577-1, Radiation protection instrumentation — Radon and radon decay product measuring
instruments — Part 1: General principles
IEC 61577-3, Radiation protection instrumentation — Radon and radon decay product measuring
instruments — Part 3: Specific requirements for radon decay product measuring instruments
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 11665-1 apply.
ISO 11665-3:2020(E)
3.2 Symbols
For the purposes of this document, the symbols given in ISO 11665-1 and the following apply.
C activity concentration of the nuclide i, in becquerels per cubic metre
i
E alpha particle energy produced by the disintegration of the nuclide i, in joules
AE,i
E total alpha particle energy potentially produced by the nuclide i, in joules
AEt,i
E potential alpha energy of the nuclide i, in joules
PAE,i
E potential alpha energy concentration of the nuclide i, in joules per cubic metre
PAEC,i
*
decision threshold of the potential alpha energy concentration of the nuclide i, in joules per
E
PAEC,i
cubic metre
#
detection limit of the of the potential alpha energy concentration of the nuclide i, in joules
E
PAEC,i
per cubic metre

lower limit of the confidence interval of the potential alpha energy concentration of the nu-
E
PAEC,i
clide i, in joules per cubic metre

upper limit of the confidence interval of the potential alpha energy concentration of the
E
PAEC,i
nuclide i, in joules per cubic metre
th
I j number of gross counts obtained between times t and t
j j cj
th
I j number of background counts obtained between times t and t
0,j j cj
th
k coefficient related to the j number of gross count for radon decay product i, depending on
i,j
the decay constants of the radon decay products, the sampling duration, t , and the times t
s j
and t , per square second
cj
N number of atoms of the nuclide i
i
n counting number depending on the gross alpha counting protocol used
Q sampling flowrate, in cubic metres per second
t end time of counting j, in seconds
cj
t start time of counting j, in seconds
j
t sampling duration, in seconds
s
U expanded uncertainty calculated by U = k⋅u( ) with k = 2
u( ) standard uncertainty associated with the measurement result
u ( ) relative standard uncertainty
rel
V sampled volume, in cubic metres
ε counting efficiency, in pulses per disintegration
c
λ decay constant of the nuclide i, per second
i
2 © ISO 2020 – All rights reserved

ISO 11665-3:2020(E)
4 Principle of the measurement method
Spot measurement of the potential alpha energy concentration of short-lived radon-222 decay products
is based on the following elements:
a) grab sampling, at time t, of short-lived radon decay products contained in a volume of air
representative of the atmosphere under investigation, using a high-efficiency filtering membrane;
b) repeated gross alpha measurements of the collected decay products using a detector sensitive to
alpha particles; the counting stage starts after sampling has stopped;
c) calculation of the activity concentrations of the radon decay products using the laws of radioactive
decay and the counting results from a preset duration, repeated at given times.
The gross alpha measurement method quantifies alpha particles emitted by short-lived radon decay
222 218
products. The Rn decay product chain shows that 99,98 % of the decays of Po result in the emission
214 214
of alpha particles. It can, therefore, be considered as a pure alpha emitter. Pb and Bi are not alpha
emitters, but they contribute to the appearance of alpha particles from the decay of Po.
After collecting the air sample, the gross alpha activity is measured for various counting durations.
Because of the fast decay of radon decay products, the isotopic composition of a sample rapidly changes
during collection as well as during the counting durations. Repeated measurements of the gross alpha
activity are necessary in order to describe the decay of the sample and thereby calculate the amounts of
the various decay products which were originally collected in the air sample.
NOTE Although Rn and its decay products are usually found in higher quantity, environmental air
samples can also contain significant activity of radonuclides of the Rn decay chain as well as other airborne
long-lived radionuclides. In such cases, the formulas and procedures given in this document need to be adapted
to take into account these additional radionuclides.
5 Equipment
The apparatus shall include a sampling system and a detection system composed of a detector
connected to a counting system (see Figure 1). The measuring devices used shall be in accordance with
IEC 61577-1 and IEC 61577-3.
The sampling system shall include the following components:
a) an open filter holder allowing fast and easy removal of the filter after sampling;
b) a pump;
c) a high-efficiency particulate air filter (HEPA filter with a minimum efficiency of 99,97 % for a
particle size of 0,3 µm);
d) a flowmeter and a chronometer;
Possible detectors include the following:
— a photomultiplier associated with a sensitive scintillation surface [for example ZnS(Ag)];
— a silicon semi-conductor that is sensitive to alpha particles.
The detector, connected to a pulse counting system, shall have a sensitive detection surface at least
equal in diameter to the filtering membrane.
...