Evaluating the performance of continuous air monitors - Part 2: Air monitors based on flow-through sampling techniques without accumulation (ISO/TR 22930-2:2020)

The use of a continuous air monitor (CAM) is mainly motivated by the need to be alerted quickly and in the most accurate way possible with an acceptable false alarm rate when significant activity concentration value is exceeded, in order to take appropriate measures to reduce exposure of those involved.
The performance of this CAM does not only depend on the metrological aspect characterized by the decision threshold, the limit of detection and the measurement uncertainties but also on its dynamic capacity characterized by its response time as well as on the minimum detectable activity concentration corresponding to an acceptable false alarm rate.
The ideal performance is to have a minimum detectable activity concentration as low as possible associated with a very short response time, but unfortunately these two criteria are in opposition. It is therefore important that the CAM and the choice of the adjustment parameters and the alarm levels be in line with the radiation protection objectives.
This document describes
—   the dynamic behaviour and the determination of the response time,
—   the determination of the characteristic limits (decision threshold, detection limit, limits of the coverage interval), and
—   a possible way to determine the minimum detectable activity concentration and the alarms setup.
Finally the annexes of this document show actual examples of CAM data which illustrate how to quantify the CAM performance by determining the response time, the characteristics limits, the minimum detectable activity concentration and the alarms setup.

Ermittlung der Leistungsfähigkeit kontinuierlicher Luftmonitore - Teil 2: Luftmonitore basierend auf Durchfluss-Sammeltechnik ohne Anreicherung (ISO/TR 22930-2:2020)

Évaluation des performances des dispositifs de surveillance de l'air en continu - Partie 2: Dispositifs de surveillance de l’air basés sur des techniques d’échantillonnage par circulation sans accumulation (ISO/TR 22930-2:2020)

Ugotavljanje zmogljivosti neprekinjeno delujočih zračnih nadzornikov - 2. del: Zračni nadzorniki na podlagi tehnik vzorčenja pretoka zraka brez kopičenja (ISO/TR 22930-2:2020)

General Information

Status
Published
Public Enquiry End Date
14-Jul-2021
Publication Date
19-Sep-2021
Technical Committee
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
15-Sep-2021
Due Date
20-Nov-2021
Completion Date
20-Sep-2021

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SLOVENSKI STANDARD
SIST-TP CEN ISO/TR 22930-2:2021
01-november-2021
Ugotavljanje zmogljivosti neprekinjeno delujočih zračnih nadzornikov - 2. del:
Zračni nadzorniki na podlagi tehnik vzorčenja pretoka zraka brez kopičenja
(ISO/TR 22930-2:2020)

Evaluating the performance of continuous air monitors - Part 2: Air monitors based on

flow-through sampling techniques without accumulation (ISO/TR 22930-2:2020)

Ermittlung der Leistungsfähigkeit kontinuierlicher Luftmonitore - Teil 2: Luftmonitore

basierend auf Durchfluss-Sammeltechnik ohne Anreicherung (ISO/TR 22930-2:2020)

Évaluation des performances des dispositifs de surveillance de l'air en continu - Partie 2:

Dispositifs de surveillance de l’air basés sur des techniques d’échantillonnage par

circulation sans accumulation (ISO/TR 22930-2:2020)
Ta slovenski standard je istoveten z: CEN ISO/TR 22930-2:2021
ICS:
13.280 Varstvo pred sevanjem Radiation protection
SIST-TP CEN ISO/TR 22930-2:2021 en,fr,de

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

---------------------- Page: 1 ----------------------
SIST-TP CEN ISO/TR 22930-2:2021
---------------------- Page: 2 ----------------------
SIST-TP CEN ISO/TR 22930-2:2021
CEN ISO/TR 22930-2
TECHNICAL REPORT
RAPPORT TECHNIQUE
August 2021
TECHNISCHER BERICHT
ICS 13.280
English Version
Evaluating the performance of continuous air monitors -
Part 2: Air monitors based on flow-through sampling
techniques without accumulation (ISO/TR 22930-2:2020)

Évaluation des performances des dispositifs de Ermittlung der Leistungsfähigkeit kontinuierlicher

surveillance de l'air en continu - Partie 2: Dispositifs de Luftmonitore - Teil 2: Luftmonitore basierend auf

surveillance de l'air basés sur des techniques Durchfluss-Sammeltechnik ohne Anreicherung

d'échantillonnage par circulation sans accumulation (ISO/TR 22930-2:2020)
(ISO/TR 22930-2:2020)

This Technical Report was approved by CEN on 16 August 2021. It has been drawn up by the Technical Committee CEN/TC 430.

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

© 2021 CEN All rights of exploitation in any form and by any means reserved Ref. No. CEN ISO/TR 22930-2:2021 E

worldwide for CEN national Members.
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SIST-TP CEN ISO/TR 22930-2:2021
CEN ISO/TR 22930-2:2021 (E)
Contents Page

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

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SIST-TP CEN ISO/TR 22930-2:2021
CEN ISO/TR 22930-2:2021 (E)
European foreword

The text of ISO/TR 22930-2:2020 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 CEN ISO/TR 22930-2:2021 by Technical Committee

CEN/TC 430 “Nuclear energy, nuclear technologies, and radiological protection” the secretariat of

which is held by AFNOR.

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.

Any feedback and questions on this document should be directed to the users’ national standards body.

A complete listing of these bodies can be found on the CEN website.
Endorsement notice

The text of ISO/TR 22930-2:2020 has been approved by CEN as CEN ISO/TR 22930-2:2021 without any

modification.
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SIST-TP CEN ISO/TR 22930-2:2021
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SIST-TP CEN ISO/TR 22930-2:2021
TECHNICAL ISO/TR
REPORT 22930-2
First edition
2020-05
Evaluating the performance of
continuous air monitors —
Part 2:
Air monitors based on flow-through
sampling techniques without
accumulation
Évaluation de la performance des dispositifs de surveillance de l'air
en continu —
Partie 2: Moniteurs d'air basés sur des techniques d'échantillonnage
par circulation sans accumulation
Reference number
ISO/TR 22930-2:2020(E)
ISO 2020
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
Contents Page

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

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

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

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

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Symbols .......................................................................................................................................................................................................................... 4

5 Measuring principle .......................................................................................................................................................................................... 6

6 Study of dynamic behaviour ..................................................................................................................................................................... 7

7 Evaluation of the characteristic limits ........................................................................................................................................13

7.1 General ........................................................................................................................................................................................................13

7.2 Single detector ......................................................................................................................................................................................13

7.2.1 General...................................................................................................................................................................................13

7.2.2 Definition of the model ............................................................................................................................................14

7.2.3 Standard uncertainty ................................................................................................................................................14

7.2.4 Decision threshold.......................................................................................................................................................15

7.2.5 Detection limit ................................................................................................................................................................17

7.2.6 Limits of the coverage interval .........................................................................................................................17

7.3 Double detector ...................................................................................................................................................................................17

7.3.1 General...................................................................................................................................................................................17

7.3.2 Definition of the model ............................................................................................................................................18

7.3.3 Standard uncertainty ................................................................................................................................................18

7.3.4 Decision threshold.......................................................................................................................................................19

7.3.5 Detection limit ................................................................................................................................................................20

7.3.6 Limits of the coverage interval .........................................................................................................................20

8 Alarms setup, minimum detectable concentration and potential missed exposure ..................20

Annex A (informative) Application example: Single detector with a proportional counter ....................23

Annex B (informative) Application example: Double detector in current mode .................................................26

Bibliography .............................................................................................................................................................................................................................32

© ISO 2020 – All rights reserved iii
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: www .iso .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,

and radiological protection, Subcommittee SC 2, Radiological protection.

A list of all the parts in the ISO/TR 22930 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
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
Introduction

Sampling and monitoring of airborne activity concentration in workplaces are critically important for

maintaining worker safety at facilities where dispersible radioactive substances are used.

The first indication of a radioactive substance dispersion event comes, in general, from a continuous

air monitor (CAM) and its associated alarm levels. In general, the response of a CAM is delayed in time

compared to the actual situation of release.

The knowledge of a few factors is needed to interpret the response of a CAM and to select the appropriate

CAM type and its operating parameters.

The role of the radiation protection officer is to select the appropriate CAM, to determine when effective

release of radioactive substances occurs, to interpret measurement results and to take corrective

action appropriate to the severity of the release.

The objective of ISO/TR 22930 series is to assist radiation protection officer in evaluating the

performance of a CAM.

ISO/TR 22930 series describes the factors and operating parameters and how they influence the

response of a CAM.

This document deals with monitoring systems based on flow-through sampling techniques without

accumulation.
© ISO 2020 – All rights reserved v
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SIST-TP CEN ISO/TR 22930-2:2021
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SIST-TP CEN ISO/TR 22930-2:2021
TECHNICAL REPORT ISO/TR 22930-2:2020(E)
Evaluating the performance of continuous air monitors —
Part 2:
Air monitors based on flow-through sampling techniques
without accumulation
1 Scope

The use of a continuous air monitor (CAM) is mainly motivated by the need to be alerted quickly

and in the most accurate way possible with an acceptable false alarm rate when significant activity

concentration value is exceeded, in order to take appropriate measures to reduce exposure of those

involved.

The performance of this CAM does not only depend on the metrological aspect characterized by the

decision threshold, the limit of detection and the measurement uncertainties but also on its dynamic

capacity characterized by its response time as well as on the minimum detectable activity concentration

corresponding to an acceptable false alarm rate.

The ideal performance is to have a minimum detectable activity concentration as low as possible

associated with a very short response time, but unfortunately these two criteria are in opposition. It is

therefore important that the CAM and the choice of the adjustment parameters and the alarm levels be

in line with the radiation protection objectives.
This document describes
— the dynamic behaviour and the determination of the response time,

— the determination of the characteristic limits (decision threshold, detection limit, limits of the

coverage interval), and

— a possible way to determine the minimum detectable activity concentration and the alarms setup.

Finally the annexes of this document show actual examples of CAM data which illustrate how to quantify

the CAM performance by determining the response time, the characteristics limits, the minimum

detectable activity concentration and the alarms setup.
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 11929-1, Determination of the characteristic limits (decision threshold, detection limit and limits of

the coverage interval) for measurements of ionizing radiation — Fundamentals and application — Part 1:

Elementary applications

ISO 16639, Surveillance of the activity concentrations of airborne radioactive substances in the workplace

of nuclear facilities

IEC 60761-1, Equipment for continuous monitoring of radioactivity in gaseous effluents — Part 1: General

requirements
© ISO 2020 – All rights reserved 1
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 11929-1, ISO 16639,

IEC 60761-1 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www. iso. org/o bp
— IEC Electropedia: available at http:// www.e lectropedia. org/
3.1
annual limit on intake
ALI

derived limit for the amount of radioactive substance (in Bq) taken into the body of an adult worker by

inhalation or ingestion in a year
[SOURCE: ISO 16639:2017, 3.7]
3.2
continuous air monitor
CAM

instrument that continuously monitors the airborne activity concentration on a near real-time basis

[SOURCE: ISO 16639:2017, 3.10]
3.3
decision threshold

value of the estimator of the measurand, which when exceeded by the result of an actual measurement

using a given measurement procedure of a measurand quantifying a physical effect, it is decided that

the physical effect is present

Note 1 to entry: The decision threshold is defined such that in cases where the measurement result, y, exceeds

the decision threshold, y*, the probability of a wrong decision, namely that the true value of the measurand is not

zero if in fact it is zero, is less or equal to a chosen probability α.

Note 2 to entry: If the result, y, is below the decision threshold, y*, it is decided to conclude that the result cannot

be attributed to the physical effect; nevertheless, it cannot be concluded that it is absent.

[SOURCE: ISO 11929-1:2019, 3.12]
3.4
derived air concentration
DAC

concentration of a radionuclide in air that, if breathed over the period of a work year, would result in the

intake of one ALI for that radionuclide

Note 1 to entry: The DAC is calculated by dividing the ALI by the volume of air breathed by reference man under

light-activity work during a working year (in Bq m ).

Note 2 to entry: The parameter values recommended by the International Commission on Radiological Protection

3 −1 3

for calculating the DAC are a breathing rate of 1,2 m ·h and a working year of 2 000 h (i.e. 2 400 m ).

Note 3 to entry: The air concentration can be expressed in terms of a number of DAC. For example, if the DAC for

−3 −3

a given radionuclide in a particular form is 0,2 Bq m and the observed concentration is 1,0 Bq m , then the

observed concentration can also be expressed as 5 DAC (i.e. 1,0 divided by 0,2).

Note 4 to entry: The derived air concentration-hour (DAC-hour) is an integrated exposure and is the product of the

concentration of a radioactive substance in air (expressed as a fraction or multiple of DAC for each radionuclide)

and the time of exposure to that radionuclide, in hours.
[SOURCE: ISO 16639:2017, 3.12]
2 © ISO 2020 – All rights reserved
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
3.5
detection alarm level

value of time-integrated activity concentration activity concentration corresponding to an acceptable

false alarm rate
Note 1 to entry: When S0 increases false alarm rate decreases.

Note 2 to entry: Others values of alarm level higher than S0 can also be set up for operational reasons.

3.6
detection limit

smallest true value of the measurand which ensures a specified probability of being detectable by the

measurement procedure

Note 1 to entry: With the decision threshold according to 3.3, the detection limit is the smallest true value of the

measurand for which the probability of wrongly deciding that the true value of the measurand is zero is equal to

a specified value, β, when, in fact, the true value of the measurand is not zero. The probability of being detectable

is consequently (1−β).

Note 2 to entry: The terms detection limit and decision threshold are used in an ambiguous way in different

standards (e.g. standards related to chemical analysis or quality assurance). If these terms are referred to one

has to state according to which standard they are used.
[SOURCE: ISO 11929-1:2019, 3.13]
3.7
limits of the coverage interval
values which define a coverage interval

Note 1 to entry: The limits are calculated in the ISO 11929 series to contain the true value of the measurand with

a specified probability (1−γ).

Note 2 to entry: The definition of a coverage interval is ambiguous without further stipulations. In this standard

two alternatives, namely the probabilistically symmetric and the shortest coverage interval are used.

Note 3 to entry: the coverage interval is defined in ISO 11929-1:2019, 3.4, as the interval containing the set of true

quantity values of a measurand with a stated probability, based on the information available.

[SOURCE: ISO 11929-1:2019, 3.16 modified – Note 3 to entry has been added]
3.8
measurand
quantity intended to be measured
[SOURCE: ISO 11929-1:2019, 3.3]
3.9
minimum detectable concentration

time-integrated activity concentration or activity concentration measurements and their associated

coverage intervals for a given probability (1−γ) corresponding to the first alarm level S0

3.10
model of evaluation

set of mathematical relationships between all measured and other quantities involved in the evaluation

of measurements
[SOURCE: ISO 11929-1:2019, 3.11]
© ISO 2020 – All rights reserved 3
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
3.11
potential missed exposure
PME

time-integrated activity concentration or maximum activity concentration, as applicable, that can

acceptably be missed

Note 1 to entry: the value of PME is defined according to ALARA/ALARP principles, and below legal limits.

Note 2 to entry: In order to be alerted when a measurement is likely to exceed the value of PME, an alarm level S1

is set up. The PME is then the upper limit of the coverage interval for a given probability (1−γ) of time-integrated

activity concentration or activity concentration measurements corresponding to S1.

[SOURCE: ISO 16639:2017, 3.18]
3.12
response time

time required after a step variation in the measured quantity for the output signal variation to reach a

given percentage for the first time, usually 90 %, of its final value

Note 1 to entry: The intrinsic response time is related to the measurement principle and its associated model of

evaluation of an ideal detector (without taking account of the counting time of the detector).

[SOURCE: IEC 60761-1:2002, 3.15]
4 Symbols
at() Activity going through the detection volume at a time t, in Bq
c Activity concentration, in Bq·m
c Actual activity concentration, in Bq·m
Decision threshold of the activity concentration, in Bq·m
Detection limit of the activity concentration, in Bq·m

Lower limit of the coverage interval of the activity concentration for a given prob-

ability (1−γ), in Bq·m

Upper limit of the coverage interval of the activity concentration for a given prob-

ability (1−γ), in Bq·m
ct Activity concentration measured at a time t, in Bq·m
ct Actual activity concentration measured at a time t, in Bq·m
c Gross primary measurement of the activity concentration, in Bq·m
c Minimum detectable activity concentration, in Bq·m
min

Lower limit of the coverage interval of the minimum detectable activity concentra-

min
tion for a given probability (1−γ), in Bq·m

Upper limit of the coverage interval the minimum detectable activity concentration

min
for a given probability (1−γ), in Bq·m
c Activity concentration of the i measurement of a series of gross measurements
0,i
(with i = 1, …, n) which represent a background situation, in Bq·m
Mean value of c , in Bq·m
0,i
4 © ISO 2020 – All rights reserved
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
I Minimum amount of current registered by the measuring detector (with
min
min
I = in A
min
I Minimum amount of current registered by the compensating detector (with
minc, d
minc, d
I = ), in A
minc, d
Ccd
() Instantaneous gross current of the measuring detector at a time t, in A

Gross current during the counting time t of the measuring detector at a time t, in A

It,,tI
gC g
It() Instantaneous gross current of the compensating detector at a time t, in A
gc, d

Gross current during the counting time t of the compensating detector at a time t, in A

It,,tI
C,cd
gc,,dC cd gc, d
I Background current of the measuring detector, in A
I Background current of the compensating detector, in A
0,cd
K Detection alarm setup parameter corresponding to the chosen acceptable false
alarm rate level, dimensionless
k Quantile of a standard normal distribution, if kk= , dimensionless
11−−αβ

k Quantile of a standard normal distribution for a probability (1−α), dimensionless

1−α

k Quantile of a standard normal distribution for a probability (1−β), dimensionless

1−β
k γ
 
Quantile of a standard normal distribution for a probability 1− , dimensionless
1−  
2  
N Number of atoms on the media filter, dimensionless

Gross count during the counting time t of the measuring detector at a time t, di-

nt,t
mensionless

Q Minimum amount of electric charge that induces a pulse registered by the measuring

min
detector, in C

Q Minimum amount of electric charge that induces a pulse registered by the compen-

minc, d
sating detector, in C
3 −1
q Flow rate, in m ·s
rt() Instantaneous gross count rate of the measuring detector at a time t, in s

Gross count rate during the counting time t of the measuring detector at a time t, in s

rt,,tr
gC g
rt Instantaneous gross count rate of the compensating detector at a time t, in s
gc, d
Gross count rate during the counting time t of the compensating detector at a
rt,,tr
() C,cd
gc,,dC cd gc, d
time t, in s
r Background count rate of the measuring detector, in s
r Background count rate of the compensating detector, in s
0,cd

s Standard deviation of the activity concentration at a series of i measurements which

represent a background situation
© ISO 2020 – All rights reserved 5
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
t Counting time of the measuring detector, in s
Counting time of the compensating detector, in s
Cc, d
t Duration of airborne release, in s
t Response time, in s
t Intrinsic response time, in s
t Counting time of the measuring detector for background measurement, in s
t Counting time of the compensating detector for background measurement, in s
0,cd
t Half-life, in s
12/
Detection volume, in m
−3 −3 −1
w Calibration factor, in Bq·m ·s or Bq·m ·A

δ Correction factor related to sampling (sampling point representativity, radioactive

decay, …), dimensionless
−1 −1 −1
ε Detector efficiency, in Bq ·s or A·Bq
λ Decay constant, in s
5 Measuring principle

A representative sample of ambient air to be monitored containing an activity concentration ct at a

time t is continuously captured through a transport line then goes through a detection volume without

being retained. In parallel, a detector continuously measures the activity going through the detection

volume. Then a processing algorithm calculates the activity concentration ct() and the suited alarms

on the basis of the evolution of the activity going through the detection volume of air sampled and the

installation or not of an ambient compensating detector. The processing algorithm can also, if necessary,

take into account influence quantities which may perturb the measurement result (see Figure 1).

6 © ISO 2020 – All rights reserved
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SIST-TP CEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
Key
1 transport line
2 detector
3 sampling pump
4 media filter
5 processing algorithm
6 alarm processing unit
Figure 1 — Model of the sampling and alarming
6 Study of dynamic behaviour

This clause describes the evolution over time of the activity concentration ct during the sudden

app
...

SLOVENSKI STANDARD
kSIST-TP FprCEN ISO/TR 22930-2:2021
01-julij-2021
Ugotavljanje zmogljivosti neprekinjeno delujočih zračnih nadzornikov - 2. del:
Zračni nadzorniki na podlagi tehnik vzorčenja pretoka zraka brez kopičenja
(ISO/TR 22930-2:2020)

Evaluating the performance of continuous air monitors - Part 2: Air monitors based on

flow-through sampling techniques without accumulation (ISO/TR 22930-2:2020)

Ermittlung der Leistungsfähigkeit kontinuierlicher Luftmonitore - Teil 2: Luftmonitore

basierend auf Durchfluss-Sammeltechnik ohne Anreicherung (ISO/TR 22930-2:2020)

Évaluation des performances des dispositifs de surveillance de l'air en continu - Partie 2:

Dispositifs de surveillance de l’air basés sur des techniques d’échantillonnage par

circulation sans accumulation (ISO/TR 22930-2:2020)
Ta slovenski standard je istoveten z: FprCEN ISO/TR 22930-2
ICS:
13.280 Varstvo pred sevanjem Radiation protection
kSIST-TP FprCEN ISO/TR 22930-2:2021 en,fr,de

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

---------------------- Page: 1 ----------------------
kSIST-TP FprCEN ISO/TR 22930-2:2021
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kSIST-TP FprCEN ISO/TR 22930-2:2021
TECHNICAL ISO/TR
REPORT 22930-2
First edition
2020-05
Evaluating the performance of
continuous air monitors —
Part 2:
Air monitors based on flow-through
sampling techniques without
accumulation
Évaluation de la performance des dispositifs de surveillance de l'air
en continu —
Partie 2: Moniteurs d'air basés sur des techniques d'échantillonnage
par circulation sans accumulation
Reference number
ISO/TR 22930-2:2020(E)
ISO 2020
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kSIST-TP FprCEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
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© ISO 2020

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Published in Switzerland
ii © ISO 2020 – All rights reserved
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Contents Page

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

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

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

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

3 Terms and definitions ..................................................................................................................................................................................... 2

4 Symbols .......................................................................................................................................................................................................................... 4

5 Measuring principle .......................................................................................................................................................................................... 6

6 Study of dynamic behaviour ..................................................................................................................................................................... 7

7 Evaluation of the characteristic limits ........................................................................................................................................13

7.1 General ........................................................................................................................................................................................................13

7.2 Single detector ......................................................................................................................................................................................13

7.2.1 General...................................................................................................................................................................................13

7.2.2 Definition of the model ............................................................................................................................................14

7.2.3 Standard uncertainty ................................................................................................................................................14

7.2.4 Decision threshold.......................................................................................................................................................15

7.2.5 Detection limit ................................................................................................................................................................17

7.2.6 Limits of the coverage interval .........................................................................................................................17

7.3 Double detector ...................................................................................................................................................................................17

7.3.1 General...................................................................................................................................................................................17

7.3.2 Definition of the model ............................................................................................................................................18

7.3.3 Standard uncertainty ................................................................................................................................................18

7.3.4 Decision threshold.......................................................................................................................................................19

7.3.5 Detection limit ................................................................................................................................................................20

7.3.6 Limits of the coverage interval .........................................................................................................................20

8 Alarms setup, minimum detectable concentration and potential missed exposure ..................20

Annex A (informative) Application example: Single detector with a proportional counter ....................23

Annex B (informative) Application example: Double detector in current mode .................................................26

Bibliography .............................................................................................................................................................................................................................32

© ISO 2020 – All rights reserved iii
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Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following

URL: www .iso .org/ iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 85, Nuclear energy, nuclear technologies,

and radiological protection, Subcommittee SC 2, Radiological protection.

A list of all the parts in the ISO/TR 22930 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.
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kSIST-TP FprCEN ISO/TR 22930-2:2021
ISO/TR 22930-2:2020(E)
Introduction

Sampling and monitoring of airborne activity concentration in workplaces are critically important for

maintaining worker safety at facilities where dispersible radioactive substances are used.

The first indication of a radioactive substance dispersion event comes, in general, from a continuous

air monitor (CAM) and its associated alarm levels. In general, the response of a CAM is delayed in time

compared to the actual situation of release.

The knowledge of a few factors is needed to interpret the response of a CAM and to select the appropriate

CAM type and its operating parameters.

The role of the radiation protection officer is to select the appropriate CAM, to determine when effective

release of radioactive substances occurs, to interpret measurement results and to take corrective

action appropriate to the severity of the release.

The objective of ISO/TR 22930 series is to assist radiation protection officer in evaluating the

performance of a CAM.

ISO/TR 22930 series describes the factors and operating parameters and how they influence the

response of a CAM.

This document deals with monitoring systems based on flow-through sampling techniques without

accumulation.
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kSIST-TP FprCEN ISO/TR 22930-2:2021
TECHNICAL REPORT ISO/TR 22930-2:2020(E)
Evaluating the performance of continuous air monitors —
Part 2:
Air monitors based on flow-through sampling techniques
without accumulation
1 Scope

The use of a continuous air monitor (CAM) is mainly motivated by the need to be alerted quickly

and in the most accurate way possible with an acceptable false alarm rate when significant activity

concentration value is exceeded, in order to take appropriate measures to reduce exposure of those

involved.

The performance of this CAM does not only depend on the metrological aspect characterized by the

decision threshold, the limit of detection and the measurement uncertainties but also on its dynamic

capacity characterized by its response time as well as on the minimum detectable activity concentration

corresponding to an acceptable false alarm rate.

The ideal performance is to have a minimum detectable activity concentration as low as possible

associated with a very short response time, but unfortunately these two criteria are in opposition. It is

therefore important that the CAM and the choice of the adjustment parameters and the alarm levels be

in line with the radiation protection objectives.
This document describes
— the dynamic behaviour and the determination of the response time,

— the determination of the characteristic limits (decision threshold, detection limit, limits of the

coverage interval), and

— a possible way to determine the minimum detectable activity concentration and the alarms setup.

Finally the annexes of this document show actual examples of CAM data which illustrate how to quantify

the CAM performance by determining the response time, the characteristics limits, the minimum

detectable activity concentration and the alarms setup.
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 11929-1, Determination of the characteristic limits (decision threshold, detection limit and limits of

the coverage interval) for measurements of ionizing radiation — Fundamentals and application — Part 1:

Elementary applications

ISO 16639, Surveillance of the activity concentrations of airborne radioactive substances in the workplace

of nuclear facilities

IEC 60761-1, Equipment for continuous monitoring of radioactivity in gaseous effluents — Part 1: General

requirements
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3 Terms and definitions

For the purposes of this document, the terms and definitions given in ISO 11929-1, ISO 16639,

IEC 60761-1 and the following apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www. iso. org/o bp
— IEC Electropedia: available at http:// www.e lectropedia. org/
3.1
annual limit on intake
ALI

derived limit for the amount of radioactive substance (in Bq) taken into the body of an adult worker by

inhalation or ingestion in a year
[SOURCE: ISO 16639:2017, 3.7]
3.2
continuous air monitor
CAM

instrument that continuously monitors the airborne activity concentration on a near real-time basis

[SOURCE: ISO 16639:2017, 3.10]
3.3
decision threshold

value of the estimator of the measurand, which when exceeded by the result of an actual measurement

using a given measurement procedure of a measurand quantifying a physical effect, it is decided that

the physical effect is present

Note 1 to entry: The decision threshold is defined such that in cases where the measurement result, y, exceeds

the decision threshold, y*, the probability of a wrong decision, namely that the true value of the measurand is not

zero if in fact it is zero, is less or equal to a chosen probability α.

Note 2 to entry: If the result, y, is below the decision threshold, y*, it is decided to conclude that the result cannot

be attributed to the physical effect; nevertheless, it cannot be concluded that it is absent.

[SOURCE: ISO 11929-1:2019, 3.12]
3.4
derived air concentration
DAC

concentration of a radionuclide in air that, if breathed over the period of a work year, would result in the

intake of one ALI for that radionuclide

Note 1 to entry: The DAC is calculated by dividing the ALI by the volume of air breathed by reference man under

light-activity work during a working year (in Bq m ).

Note 2 to entry: The parameter values recommended by the International Commission on Radiological Protection

3 −1 3

for calculating the DAC are a breathing rate of 1,2 m ·h and a working year of 2 000 h (i.e. 2 400 m ).

Note 3 to entry: The air concentration can be expressed in terms of a number of DAC. For example, if the DAC for

−3 −3

a given radionuclide in a particular form is 0,2 Bq m and the observed concentration is 1,0 Bq m , then the

observed concentration can also be expressed as 5 DAC (i.e. 1,0 divided by 0,2).

Note 4 to entry: The derived air concentration-hour (DAC-hour) is an integrated exposure and is the product of the

concentration of a radioactive substance in air (expressed as a fraction or multiple of DAC for each radionuclide)

and the time of exposure to that radionuclide, in hours.
[SOURCE: ISO 16639:2017, 3.12]
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3.5
detection alarm level

value of time-integrated activity concentration activity concentration corresponding to an acceptable

false alarm rate
Note 1 to entry: When S0 increases false alarm rate decreases.

Note 2 to entry: Others values of alarm level higher than S0 can also be set up for operational reasons.

3.6
detection limit

smallest true value of the measurand which ensures a specified probability of being detectable by the

measurement procedure

Note 1 to entry: With the decision threshold according to 3.3, the detection limit is the smallest true value of the

measurand for which the probability of wrongly deciding that the true value of the measurand is zero is equal to

a specified value, β, when, in fact, the true value of the measurand is not zero. The probability of being detectable

is consequently (1−β).

Note 2 to entry: The terms detection limit and decision threshold are used in an ambiguous way in different

standards (e.g. standards related to chemical analysis or quality assurance). If these terms are referred to one

has to state according to which standard they are used.
[SOURCE: ISO 11929-1:2019, 3.13]
3.7
limits of the coverage interval
values which define a coverage interval

Note 1 to entry: The limits are calculated in the ISO 11929 series to contain the true value of the measurand with

a specified probability (1−γ).

Note 2 to entry: The definition of a coverage interval is ambiguous without further stipulations. In this standard

two alternatives, namely the probabilistically symmetric and the shortest coverage interval are used.

Note 3 to entry: the coverage interval is defined in ISO 11929-1:2019, 3.4, as the interval containing the set of true

quantity values of a measurand with a stated probability, based on the information available.

[SOURCE: ISO 11929-1:2019, 3.16 modified – Note 3 to entry has been added]
3.8
measurand
quantity intended to be measured
[SOURCE: ISO 11929-1:2019, 3.3]
3.9
minimum detectable concentration

time-integrated activity concentration or activity concentration measurements and their associated

coverage intervals for a given probability (1−γ) corresponding to the first alarm level S0

3.10
model of evaluation

set of mathematical relationships between all measured and other quantities involved in the evaluation

of measurements
[SOURCE: ISO 11929-1:2019, 3.11]
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3.11
potential missed exposure
PME

time-integrated activity concentration or maximum activity concentration, as applicable, that can

acceptably be missed

Note 1 to entry: the value of PME is defined according to ALARA/ALARP principles, and below legal limits.

Note 2 to entry: In order to be alerted when a measurement is likely to exceed the value of PME, an alarm level S1

is set up. The PME is then the upper limit of the coverage interval for a given probability (1−γ) of time-integrated

activity concentration or activity concentration measurements corresponding to S1.

[SOURCE: ISO 16639:2017, 3.18]
3.12
response time

time required after a step variation in the measured quantity for the output signal variation to reach a

given percentage for the first time, usually 90 %, of its final value

Note 1 to entry: The intrinsic response time is related to the measurement principle and its associated model of

evaluation of an ideal detector (without taking account of the counting time of the detector).

[SOURCE: IEC 60761-1:2002, 3.15]
4 Symbols
at() Activity going through the detection volume at a time t, in Bq
c Activity concentration, in Bq·m
c Actual activity concentration, in Bq·m
Decision threshold of the activity concentration, in Bq·m
Detection limit of the activity concentration, in Bq·m

Lower limit of the coverage interval of the activity concentration for a given prob-

ability (1−γ), in Bq·m

Upper limit of the coverage interval of the activity concentration for a given prob-

ability (1−γ), in Bq·m
ct Activity concentration measured at a time t, in Bq·m
ct Actual activity concentration measured at a time t, in Bq·m
c Gross primary measurement of the activity concentration, in Bq·m
c Minimum detectable activity concentration, in Bq·m
min

Lower limit of the coverage interval of the minimum detectable activity concentra-

min
tion for a given probability (1−γ), in Bq·m

Upper limit of the coverage interval the minimum detectable activity concentration

min
for a given probability (1−γ), in Bq·m
c Activity concentration of the i measurement of a series of gross measurements
0,i
(with i = 1, …, n) which represent a background situation, in Bq·m
Mean value of c , in Bq·m
0,i
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I Minimum amount of current registered by the measuring detector (with
min
min
I = in A
min
I Minimum amount of current registered by the compensating detector (with
minc, d
minc, d
I = ), in A
minc, d
Ccd
() Instantaneous gross current of the measuring detector at a time t, in A

Gross current during the counting time t of the measuring detector at a time t, in A

It,,tI
gC g
It() Instantaneous gross current of the compensating detector at a time t, in A
gc, d

Gross current during the counting time t of the compensating detector at a time t, in A

It,,tI
C,cd
gc,,dC cd gc, d
I Background current of the measuring detector, in A
I Background current of the compensating detector, in A
0,cd
K Detection alarm setup parameter corresponding to the chosen acceptable false
alarm rate level, dimensionless
k Quantile of a standard normal distribution, if kk= , dimensionless
11−−αβ

k Quantile of a standard normal distribution for a probability (1−α), dimensionless

1−α

k Quantile of a standard normal distribution for a probability (1−β), dimensionless

1−β
k γ
 
Quantile of a standard normal distribution for a probability 1− , dimensionless
1−  
2  
N Number of atoms on the media filter, dimensionless

Gross count during the counting time t of the measuring detector at a time t, di-

nt,t
mensionless

Q Minimum amount of electric charge that induces a pulse registered by the measuring

min
detector, in C

Q Minimum amount of electric charge that induces a pulse registered by the compen-

minc, d
sating detector, in C
3 −1
q Flow rate, in m ·s
rt() Instantaneous gross count rate of the measuring detector at a time t, in s

Gross count rate during the counting time t of the measuring detector at a time t, in s

rt,,tr
gC g
rt Instantaneous gross count rate of the compensating detector at a time t, in s
gc, d
Gross count rate during the counting time t of the compensating detector at a
rt,,tr
() C,cd
gc,,dC cd gc, d
time t, in s
r Background count rate of the measuring detector, in s
r Background count rate of the compensating detector, in s
0,cd

s Standard deviation of the activity concentration at a series of i measurements which

represent a background situation
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t Counting time of the measuring detector, in s
Counting time of the compensating detector, in s
Cc, d
t Duration of airborne release, in s
t Response time, in s
t Intrinsic response time, in s
t Counting time of the measuring detector for background measurement, in s
t Counting time of the compensating detector for background measurement, in s
0,cd
t Half-life, in s
12/
Detection volume, in m
−3 −3 −1
w Calibration factor, in Bq·m ·s or Bq·m ·A

δ Correction factor related to sampling (sampling point representativity, radioactive

decay, …), dimensionless
−1 −1 −1
ε Detector efficiency, in Bq ·s or A·Bq
λ Decay constant, in s
5 Measuring principle

A representative sample of ambient air to be monitored containing an activity concentration ct at a

time t is continuously captured through a transport line then goes through a detection volume without

being retained. In parallel, a detector continuously measures the activity going through the detection

volume. Then a processing algorithm calculates the activity concentration ct() and the suited alarms

on the basis of the evolution of the activity going through the detection volume of air sampled and the

installation or not of an ambient compensating detector. The processing algorithm can also, if necessary,

take into account influence quantities which may perturb the measurement result (see Figure 1).

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Key
1 transport line
2 detector
3 sampling pump
4 media filter
5 processing algorithm
6 alarm processing unit
Figure 1 — Model of the sampling and alarming
6 Study of dynamic behaviour

This clause describes the evolution over time of the activity concentration ct during the sudden

appearance of an actual activity concentration c . The dynamic behaviour is quantified by the

response time. The response time t is due to the intrinsic response time t related to the measurement

R RI

principle and its associated model of evaluation, the time delay provided by the counting time t of the

activity going through the detection volume, the renewal rate of the detection volume and also the

duration of the processing algorithm. This latter duration is not taken into account in this document but

it should be kept in mind.

It is considered in the following that the actual concentration to be measured c changes over time in

steps of duration t :
ct()=≤ctwhen0 ac ac F
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ct()=≥0 whentt (2)
ac F

The differential equations describing the number of atoms N of the radionuclide considered in the

detection volume of the detector can be formulated as a function of the concentration c at the

sampling point according to the following relationships:
qCδ
dNt() Nt()q
=−λNt()− when0≤ dt λ V

NOTE 1 The monitor flow rate q is taken to be constant over the interval of interest.

and
dNt() Nt()q
=−λNt − whentt≥ (4)
dt V

Moreover, the evolution of the activity present in the detection volume is given by the relationship

rt()−r
g 0
at =λNt = (5)
() ()

NOTE 2 The detector efficiency ε is supposed to be constant meaning that at any time the activity is

distributed uniformly throughout the detection volume.

Considering that N(0) = 0 at the beginning of the sampling, the solutions of the differential Formulae (3)

and (4) are:
 
 
−+λ t
εδqc
 
Dac
 V 
 
rt −=rNελ t = 1−ewhen0≤t< () ()
gD0 F
 
 
q q
   
 
−+λλt −+ ()tt−
εδqc
   
F F
Dac
 V   V 
 
rt −=rNελ t = 1−ee whentt≥ (7)
() ()
gD0 F
 
λ +
 

From the Formulae (5), (6) and (7), the model of evaluation of the activity concentration over time can

be expressed as
 
ct()= rt()−r (8)
 
εδ q

When an ionization detector is used, instead of the count rate, the current may be the output. Then the

model of evaluation of the activity concentration becomes to
 
ct()= It()−I (9)
 
εδ q
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with
 
 
−+λ t
 
 V 
 
ct()=−ct1 ewhen0≤ ac F
 
 
q q
   
 
−+λλt −+ ()tt−
   
V V
   
 
ct()=−ct1 ee when ≥t (11)
ac F
 
 

The evolution of the ratio of the activity concentration and the actual one according to Formula (10) by

considering an infinite duration release ( t → ∞) is given in Table 1.
ct()

Table 1 — Evolution of the ratio of the measured activity concentration and the actual

one according to Formula (10)
Ratio Time
% s
0 0
06, 9
λ +
23,
λ +
46, 1
λ +
...

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