IEC TR 61577-5:2019

IEC TR 61577-5 ®
Edition 1.0 2019-07
TECHNICAL
REPORT
colour
inside
Radiation protection instrumentation – Radon and radon decay product
measuring instruments –
Part 5: General properties of radon and radon decay products and their
measurement methods
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IEC TR 61577-5 ®
Edition 1.0 2019-07
TECHNICAL
REPORT
colour
inside
Radiation protection instrumentation – Radon and radon decay product

measuring instruments –
Part 5: General properties of radon and radon decay products and their

measurement methods
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 13.280 ISBN 978-2-8322-7123-0

– 2 – IEC TR 61577-5:2019  IEC:2019
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Symbols, quantities and units . 8
3.1 Symbols . 8
3.2 Quantities and units . 9
4 Radon in the environment . 9
4.1 Origin, genesis and decay . 9
4.2 Radon in the rocks and soils and its transport towards the atmosphere . 10
4.3 Radon concentration in the outdoor air. 11
4.4 Radon concentration in houses and at workplaces . 11
5 Radon decay products in the atmosphere . 12
5.1 Physical processes of decay products in gaseous media . 12
5.2 Aerosol characteristics and ventilation . 13
6 Physical and chemical properties of radon and radon decay products . 14
6.1 Physical and chemical properties . 14
6.2 Solubility of radon in liquids . 14
6.3 Radiological properties and radioactive equilibrium . 15
6.4 Interaction of alpha particles with matter and energy deposition . 17
222 220
7 Measurement of Rn and Rn and their decay products . 18
7.1 Relevant measurement quantities and units . 18
7.1.1 Activity concentration (C) . 18
7.1.2 Equilibrium equivalent activity concentration (EEC, C ) . 18
eq
7.1.3 Equilibrium factor (F) . 19
7.1.4 Exposure to radon (P ) . 19
Rn
7.1.5 Potential alpha energy (ε ) . 20
p
7.1.6 Potential alpha energy concentration (C ) . 20
p
7.1.7 Potential alpha energy exposure (P ) . 22
p
7.1.8 The unattached and attached fraction of potential alpha energy
concentration . 22
7.2 Instruments measuring airborne radon activity concentration . 22
7.3 Measurement of radon decay products . 23
7.3.1 General overview of instruments . 23
7.3.2 Sampling of the unattached radon decay products . 24
7.3.3 Counting methods for the measurement of the activity concentrations
and the potential alpha-energy concentration . 25
8 Quality assurance . 30
8.1 Definition and purpose . 30
8.2 Quality control . 31
8.3 Validation and traceability of measurements . 31
8.3.1 Validation of methods . 31
8.3.2 Type test of radon instruments . 31
8.3.3 Interlaboratory comparison . 31
8.3.4 Measurement traceability and calibration . 32
9 Determination of the measurement uncertainty, detection threshold, detection limit . 32
9.1 General . 32

9.2 Procedure for the determination . 33
Annex A (informative) Tables and Figures . 35
Annex B (informative) Radioactive decay formulae . 40
B.1 General . 40
B.2 Symbols . 40
B.3 Preliminary considerations and assumptions . 40
B.4 Build-up of filter activity during sampling . 41
B.5 Decay of the filter activity after cessation of sampling . 43
B.6 Number of alpha disintegrations registered after sampling . 44
Annex C (informative) Uncertainty analysis for the method of multiple successive
countings to determine the activity concentrations of radon and thoron decay products . 46
C.1 Symbols . 46
C.2 Uncertainties of the parameter of the model function . 46
C.3 Decision threshold . 50
C.4 Detection limit . 51
C.5 Confidence limits . 51
C.6 Best estimate and its uncertainty . 52
Bibliography . 53

st
Figure 1 – Diurnal variations of the radon activity concentration in the cellar, 1 and
nd
2 floor of a detached house measured over 12 days . 12
Figure 2 – Decay of Rn after injection of 1 000 Bq at the start time and generation
of decay products . 16
Figure 3 – Decay of Rn (Thoron) after injection of 1 000 Bq at the start time and
generation of decay products . 16
Figure 4 – Activity build-up of Rn and its decay products for a continuous supply of
Rn with a rate of 1 Bq/s (in the absence of initial activities) . 16
Figure 5 – Activity build-up of Rn (Thoron) and its decay products for a continuous
supply of Rn with a rate of 1 Bq/s (in the absence of initial activities) . 16
Figure 6 – Total stopping power of alpha particles penetrating different materials, the
graphs use data from [38] . 17
Figure 7 – Contributions of the deposition processes to the total efficiency (calculated
exemplarily for a wire screen) . 24
Figure 8 – Variation of deposition efficiency of a wire screen in dependence on air flow
velocity (calculated exemplarily for a wire screen) . 24
Figure 9 – Measurement error of the method of MARKOV given in percent for different
ratios of decay products in the air sampled . 27
Figure 10 – Method of multiple successive countings . 28
Figure A.1 – Sampling and measurement procedures commonly used for radon
instruments . 35
Figure A.2 – Sampling and measurement procedures commonly used for radon
progeny instruments . 35
Figure B.1 – Scheme for sampling and counting . 44

Table 1 – Coefficients for the calculation of the equilibrium equivalent concentration

from measured activity concentrations of radon progeny . 19
Table 2 – Potential alpha energy per atom for Rn progeny including standard
uncertainty . 21

– 4 – IEC TR 61577-5:2019  IEC:2019
Table 3 – Potential alpha energy per atom for Rn progeny including standard
uncertainty . 21
Table 4 – Time scheme for the method of Thomas [57] . 26
Table 5 – Time scheme for the method of MARKOV [63] . 27
Table A.1 – Physical and chemical characteristics [29] . 36
226 222 222
Table A.2 – Ra, Rn and radionuclides of the Rn decay chain [37] . 36
224 220 220
Table A.3 – Ra, Rn and radionuclides of the Rn decay chain [37] . 37
Table A.4 – CSDA-Range of alpha particles emitted by Radon-222 and Radon-220
decay products in different materials [38] . 37
Table A.5 – Solubility of radon in organic components [31] . 38
Table A.6 – Diffusion coefficients and diffusion lengths for radon in different materials
[79] . 38

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RADIATION PROTECTION INSTRUMENTATION – RADON
AND RADON DECAY PRODUCT MEASURING INSTRUMENTS –

Part 5: General properties of radon and radon
decay products and their measurement methods

FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC TR 61577-5, which is a Technical Report, has been prepared by subcommittee 45B:
Radiation protection instrumentation, of IEC technical committee 45: Nuclear instrumentation.
The text of this Technical Report is based on the following documents:
Enquiry draft Report on voting
45B/912/DTR 45B/926/RVDTR
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.

– 6 – IEC TR 61577-5:2019  IEC:2019
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 61577 series, published under the general title Radiation
protection instrumentation – Radon and radon decay product measuring instruments, can be
found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
 reconfirmed,
 withdrawn,
 replaced by a revised edition, or
 amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
RADIATION PROTECTION INSTRUMENTATION – RADON
AND RADON DECAY PRODUCT MEASURING INSTRUMENTS –

Part 5: General properties of radon and radon
decay products and their measurement methods

1 Scope
This part of IEC 61577 provides basic data and technical information in order to support the
design of instruments and their practical application for the measurement. The document
222 220
covers Rn as well as Rn and the short-lived decay products of both. It is an
accompanying document for the application of the technical standards series IEC 61577, and
provides physical and technical fundamentals of the measurements methods. For more
information, reference is made to the Bibliography.
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.
IEC 61577-1, Radiation protection instrumentation – Radon and radon decay product
measuring instruments – Part 1: General principles
IEC 61577-2, Radiation protection instrumentation – Radon and radon decay product
222 220
measuring instruments – Part 2: Specific requirements for Rn and Rn measuring
instruments
IEC 61577-3, Radiation protection instrumentation – Radon and radon decay product
measuring instruments – Part 3: Specific requirements for radon decay product measuring
instruments
IEC 61577-4, Radiation protection instrumentation – Radon and radon decay product
measuring instruments – Part 4: Equipment for the production of reference atmospheres
containing radon isotopes and their decay products (STAR)
IEC TR 62461:2015, Radiation protection instruments – Determination of uncertainty in
measurement
– 8 – IEC TR 61577-5:2019  IEC:2019
3 Symbols, quantities and units
3.1 Symbols
L Ostwald coefficient
Activity concentration of radon in a liquid, activity concentration of radon in
C , C
Rn,liquid Rn
-3
air in Becquerels per cubic meter (Bq·m )
Temperature of water in degrees Celsius (°C)
T
H O
Activity, activity of radionuclide i in Becquerels (Bq)
A, A
i
-1
Radioactive decay constant of radionuclide i in per second (s )
λ
i
-1
Supply rate, production rate of radionuclide i in per second (s )
q
i
Time, sampling time in seconds (s)
t, t
s
V Volume in cubic metres (m )
-
Equilibrium equivalent concentration in Becquerels per cubic metres (Bq·m
EEC, C
eq
)
Weighting coefficient of radionuclide i
k
i
-3
Potential alpha energy concentration in Joules per cubic metre (J·m )
C
p
F Equilibrium factor
-3
Exposure to radon in Becquerel hours per cubic metre (Bq·h·m )
P
Rn
Potential alpha energy in Joules (J)
ε
p
Number of atoms of radionuclide i
N
i
-3
Potential alpha energy exposure in Joule hours per cubic metre (J·h·m )
P
p
Standard uncertainty of quantity x
u(x)
U (x) Expanded uncertainty U (x) = k ⋅u(x) with the coverage factor k = 2
3 -1
v Volume flow rate of air in litres per minute (m s )
Number of counts of radionuclide i
I
i
Efficiency, sampling efficiency, sampling efficiency of radionuclide i,
ε , ε , ε , ε
s si c
counting efficiency of radionuclide i
ε
ci
Elapsed time after cessation of sampling until the beginning of time interval
α
, α
k
k, time at which the counting interval begins in seconds (s)
Elapsed time after cessation of sampling until the end of time interval k,
β ,
β
k
time at which the counting interval ends in seconds (s)
Coefficients of vector D : Number of alpha disintegrations observed during
D
k
th
the k time interval (counting period α to β )
k k
th
a (α , β ) Coefficients of matrix A : i coefficient of count determination k within the
k,i k k
limits α and β
k k
222 220
Coefficients of vector N : the five unknown Rn and Rn short-lived
N (t )
i s
t
decay products sampled and deposited onto the filter at time
s
C Coefficients of vector C: mean activity concentrations of the five short-lived

i
decay products in the sampled air

T T
A , , , D ,
A C Matrices and vectors ( A is the transposed matrix of A )
N , M
Substitutions defined in the text
κ , η
k
k,l
M Output quantity of the linear model function, h
Linear model function with the input quantities X , , X
h(X , , X )
1 T
1 T
Input quantities of the linear model function, h
X , ,X
1 T
Best estimate of the input quantities
ˆ ˆ
x , ,x
1 T
Relative standard uncertainty of a quantity x
u (x)
rel
Sensitivity coefficient
c , ,c
1 T
The indices i refer to the following radionuclides:
index i = 1 refers to Po
index i = 2 refers to Pb
214 214
index refers to Bi/ Po
i = 3
index refers to Pb
i = 4
index i = 5 refers to Bi
index ′ refers to Po
i = 5
3.2 Quantities and units
In this document, units of the International System (SI) are used . The definitions of radiation
quantities are given in IEC 60050-393 and IEC 60050-395. The corresponding old units
(non SI) are indicated in brackets.
Multiples and submultiples of SI units will be used, when practicable, according to the SI
system.
4 Radon in the environment
4.1 Origin, genesis and decay
The heavy metals uranium and thorium are natural components of the lithosphere. Both
elements can be detected in different quantities in minerals, in soils and in water. The
average concentration in the lithosphere for uranium is between 2,5 – 4 mg/kg and for thorium
about 13 mg/kg [1] . Naturally occurring uranium is a mixture of three isotopes: 99,27 % U,
235 234 238 232
0,72 % U and 0,01 % U. The primordial radionuclides U and Th are the mother
222 220
nuclides of the decay chains by which Rn and Rn are formed, respectively.
222 226 220 224 226
The direct mother nuclide of Rn is Ra and of Rn, it is Ra. Ra has formerly
gained technical importance as luminescent paint for dials of watches and instruments. The
alpha particles emitted by disintegration of radium excite a phosphor radiating luminescence
light. Ra was also applied as radiation source in medicine.

—————————
th
International Bureau of Weights and Measures: The International System of Units, 8 edition, 2006.
Numbers in square brackets refer to the Bibliography.

– 10 – IEC TR 61577-5:2019  IEC:2019
238 232
In contradiction to all other radionuclides of the U- and Th-decay chains, radon isotopes
are gaseous. Radon is soluble in water. Particularly, Rn can be enriched in groundwater, if
the aquifer layers contain elevated values of natural radioactivity (e.g. granite stone). A
technical application of the radon isotopes is not known. In medicine, radon is used for the
treatment of chronic diseases of the musculoskeletal system. As typical indication for a radon
therapy, rheumatic diseases of the joints are often cited [2].
Elevated concentrations of radon have been mostly found at underground workplaces (mining),
in radon spas or in water works. Elevated concentrations of Rn in houses and other
buildings can particularly occur, when a high concentration of Rn in soil exists, and radon
penetrates the house via entry paths in the below-ground structural elements. Elevated
exposures to Rn are mostly credited to thorium-containing building materials (e.g.
limestone) [3].
The main source for the radiation effect is not attributed to the inhalation of radon itself but to
the simultaneous inhalation of its short-lived decay products mostly attached to aerosol
222 218 214 214 214
particles. The short-lived Rn decay products are Po, Pb, Bi and Po and those
220 216 212 212 212
of Rn are Po, Pb, Bi and Po. The short-lived decay products are deposited in
218 214 212
the respiratory tract and decay there. Alpha particles emitted by Po and Po, or Bi
Po respectively, transfer their energy along the penetration way to the radiation
and
sensitive cells, which cause possible health effects. Po is an exemption. Because of its
short half-life, it disintegrates during inhalation, and does therefore not markedly contribute to
the exposure in the lung.
220 208 222
Whilst the Rn decay chain ends up with the stable lead isotope Pb, the Rn decay
210 210
chain has further stages following the short-lived decay products: Headed by Pb, Bi and
210 206
Po follows until it ultimately ends up with the stable lead isotope Pb. Because of the
long half-life of Pb of more than 20 years, the remaining radionuclides are moved out of
the respiratory tract by lung clearance, being excreted or deposited mainly in the mineral
component of the bones [4]. In view of radiation protection, the radiation effects of the long-
lived radionuclides are not relevant.
4.2 Radon in the rocks and soils and its transport towards the atmosphere
In rocks and soils, the permanent generation of radon is performed by alpha decay of radium.
Radon atoms are subject to various processes on their path from the generation up to the
atmosphere.
The emanation is the discharge of radon from the solid, mostly crystalline, phase of rocks and
soils into the free pore volume, micro cracks, and fissures of the subsoil. The quantity, which
defines the ratio between the number of radon atoms escaped the solid phase and the total
number of radon atoms created in the solid phase, is the radon emanation coefficient. The
process of discharge is initiated by the recoil due to alpha decay. The efficiency of this
process depends on the distribution of radium in the mineral grain. The main part of radon
escapes from radium located on the surface of the mineral grain or in the vicinity of the
surface with depths lower than the recoil distance. A discharge of radon inside the mineral
grain is only possible if sufficient pathways inside the grain are available. Very important for
the emanation is therefore the grain size distribution.
The presence of water can increase the radon discharge. Due to adsorption of kinetic energy,
radon atoms continue to stay in the pore water, from which it can attain the air-filled pore
volume by diffusion. Soils and rocks reach the maximum of the radon emanation at various
moistures. With the pore volume increasingly filling up with water, the part in the gas phase is
getting lower, and the connectivity of the pore volumes by menisci is disturbed. Between dry
and moisturized, the emanation can vary by a factor of 5 [5].

The movement of radon through rocks and soils is named migration. It is subject to geo-
mechanical and hydrological conditions in the subsoil (permeability, fissions, flow of ground
water and soil air). The main transport process is the diffusion, which can be supplemented by
convection as an additional process. The diffusion is the mass transport of radon through
inter-granular volumes, capillaries and fine pores caused by gradients of concentration. The
coefficient of diffusion is a measure for the displacement forced by the gradient of
concentration. In Table A.6, the effective diffusion coefficients for different materials are given.
The coefficients take into account the prolongation of diffusion pathway due to ramifications of
pores conducting the gas around the solid particles (tortuosity).
By convection, radon is transported together with carrier media, like ground waters or soil
gases. The convective radon transport can result in radon anomalies. Within the bedrock,
fissions and faults channelize the movement of radon-containing gases or ground waters,
leading to an inhomogeneous distribution of the radon concentration far away from the origin
of radon atoms.
Besides the basic availability of radon by emanation and transport from the bedrock, the
concentration of radon in the upper soil layers depends on the permeability, which in turn,
depends on the pore size distribution and the degree of saturation with moisture, and can
therefore locally and seasonally vary over several magnitudes. The discharge of radon from
soil surface into air is denoted as exhalation.
4.3 Radon concentration in the outdoor air
Weather conditions with variations in air temperature from day to night cause variations in the
outdoor radon concentration [6]. During the day the soil surface and the lower layers of the
atmosphere heat up more intensively then the upper air layers by solar radiation, thus making
the thermal stratification instable. The rising warm air results in a vertical intermixing of the
atmosphere with low radon concentrations at the day. During the night and the early hours of
the morning, the soil surface and the lower layers of the atmosphere cool down resulting in a
stable stratification of the atmosphere (inversion at night). This process reduces the vertical
intermixing of the atmosphere, which causes high radon concentration in the lower outdoor air
layers. The variation of the radon concentration between day and night is greater, the greater
the contrast in air temperature is. Measurements have shown that the day-to-night variations
in the radon concentrations are mainly provoked by fluctuations of the vertical stratification in
the atmosphere [7]. By contrast, the daily variations of the radon exhalation from the ground
do not have substantial impact on the day-to-night variations in the outdoor radon
concentrations [7].
4.4 Radon concentration in houses and at workplaces
Radon can enter a house through its substructure due to depressurization caused by the wind
load or the temperature difference between indoor and outdoor. Indoor to outdoor temperature
differences cause convective air flows, by which outdoor air flows into the building at the base

– 12 – IEC TR 61577-5:2019  IEC:2019

NOTE The maxima were measured in the early morning hours and the minima in the afternoon. The variations
have a period of 24 h. The figure indicates the time lag of the variations and the reduced concentrations in the
floors above the cellar [8].
Figure 1 – Diurnal variations of the radon activity concentration in the cellar,
st nd
1 and 2 floor of a detached house measured over 12 days
and out of the building at the upper floors or the ceiling. The architecture of the house affects
the distribution of radon throughout the building. In basements, radon-laden soil gas flows
through cracks in the floor slab and walls, block wall cavities, plumbing connections, and
sump wells. The radon concentration in the soil gas entering the house depends basically on
the geology, the content of Ra in the soil and its humidity. The transport of radon is
enhanced when buildings are under significant negative pressure, particularly at floor level
[6][7][9]. The indoor radon concentration undergoes diurnal and seasonal periods
[10][11][12][13][14]. The long-term trends resulting from the use of the building or the relevant
room(s) as well as from meteorological conditions are superimposed by stochastic fluctuations.
Figure 1 represents an example of the diurnal variations of the radon activity concentration in
the cellar, 1st and 2nd floor of a detached house measured over 12 days.
5 Radon decay products in the atmosphere
5.1 Physical processes of decay products in gaseous media
After the formation of radon decay products, they are subject to various physical and chemical
processes. The processes are described here on the example of Po, which has been
investigated extensively [15][16][17]. Measurements have shown that after formation more
than 10 % to – 60 % of Po is positively charged. Different concurrent processes act on the
fresh generated decay products: cluster formation, neutralization as well as attachment to
aerosols and on surfaces. Within a short time (<1 s) after formation, the radionuclides attach
to vapors (predominately H O) and to other trace gas molecules in the atmosphere. The thus
generated radioactive clusters are denoted as the unattached fraction of the radon decay
products, and have diameters between 0,5 nm and 3 nm [18].

2 -1
Because of their small particle size and their high diffusion coefficient between 0,005 cm ∙s
2 -1
to 0,100 cm ∙s [18], the clusters possess a high mobility. Thus making the clusters almost
independent to other transport processes in the air, as turbulence, convection, sedimentation
and distraction by electromagnetic fields. A radioactive aerosol is formed by attaching the
radioactive clusters to the existing aerosol particles in air. This process takes 1 s to 100 s [19].
The ratio of potential alpha energy of the short-lived radon progeny, which are unattached to
aerosol particles, to the potential alpha energy of the attached short-lived radon progeny
depends mainly on the aerosol particle concentration, and varies between 0,03 and 0,2 for
dwellings [19]. The ratio decreases to below 0,01 in mines due to the increasing particle
concentration [20].
5.2 Aerosol characteristics and ventilation
Atmospheric aerosol particle size distributions consist basically of three separate modes
[21][22]:
a) the nucleation (or nuclei) mode for particles with diameters smaller than 100 nm and a
modal peak in the range between 10 nm and 30 nm range,
b) the accumulation mode for particles with diameters between about 100 nm to about 1 µm
and a modal peak at about 300 nm, and
c) the coarse mode corresponding to particles with diameters larger than 1 µm.
The nucleation mode appears if particles are freshly formed or emitted. This mode has a
relatively short lifetime. By coagulation with other nuclei and accumulation mode particles,
there sizes increase and end up in the next larger mode, the accumulation mode [21]. Several
aerosol particle sources, such as cigarette smoke, gas stove, or candles, affect the particle
distribution significantly according to the properties of the particles emitted. 10 % to 20 % of
the attached activity could be assigned to the nucleation mode between 10 nm and 100 nm
[19][23]. Aerosol particles with diameters below 100 nm are also denoted as ultrafine particles.
The accumulation mode results largely from the condensation of water and other vapours, and
the attachment of particles by coagulation. This mode is stable with respect to deposition, and
has a relative long atmospheric residence time.
The coarse mode particles are usually mechanically formed, or are resuspended particles
such as windblown dust. This mode appears mainly in the outdoor environment or at
workplaces.
The aerosol particle size distributions at workplaces are influenced by the local ventilation
conditions and possibly different aerosol sources. The aerosol particle concentration depends
strongly on work activity. During the work activities in mines, the radioactive aerosol particles
tend to smaller diameters caused by the large number of particles emitted by diesel engines.
At underground workplaces (mines, show caves) the activity size distribution of attached
radon progeny can be described by a unimodal lognormal distribution specified by the activity
median aerodynamic diameter and the geometric standard deviation [20]. Measurements at
aboveground workplaces have identified a tri-modal aerosol size distribution with the focus on
the accumulation mode [23]. Depending on the work activities, the particle sources and the
ventilation, the nucleation and the coarse mode are more or less distinct [23].
In a radon atmosphere, a mixture of gaseous radon and radon decay products attached or
unattached to aerosol particles exists. But not all the decay products are available in the air
volume. Because of particle deposition and adhesion, a part of them is deposited to other
surfaces, as walls, floors or the possible inventory of the site (e.g. room). This part of
radioactivity is not inhaled and does, therefore, not contribute to the radiation effects. The
radon equilibrium factor expresses the disturbance of equilibrium between radon and its short-
lived decay products (for definition see 7.1). In real atmospheres, the equilibrium factor is
below 1. Indoor measurements have shown that the equilibrium factor varies within a 95 %
confidence interval from 0,2 to 0,7 around the mean value of 0,4 [24][25].

– 14 – IEC TR 61577-5:2019  IEC:2019
6 Physical and chemical properties of radon and radon decay products
6.1 Physical and chemical properties
As a noble gas, radon is chemically broadly inert. In the presence of Fluor, radon is not
volatile up to 230 °C, what can be caused by the formation of a radon fluoride. Radon is
soluble in water and organic solvents [26][27]. Although colourless at standard temperature
and pressure, on cooling below its freezing point of −71 °C radon emits a brilliant radio
luminescence that turns from yellow to orange-red as the temperature lowers [28][29]. An
222 -3 222
activity concentration of Rn of 100 Bq∙m is equivalent to a Rn concentration of about
7 25
5∙10 atoms per cubic metre. Taking into consideration that a gas contains more than 10
atoms per cubic metre under standard conditions, in all cases where radon is present in the
environment, it is a trace gas. Some physical and chemical properties of radon and its decay
products are given in Table A.1.
Radon is readily absorbed on charcoal, silica gel and similar adsorbing substances. Radon
can, therefore, be effectively removed from a sample air stream by collecting it on activated
charcoal cooled to the temperature of solid carbon dioxide (-78,5 °C). Radon is desorbed from
charcoal by heating to 350 °C [30].
6.2 Solubility of radon in liquids
Due to diffusion an exchange of gas molecules between the liquid and the gas volume exists
at the interface between a gas and a liquid. The transfer into the liquid is proportional to the
partial pressure of the gas. The discharge from the liquid is proportional to the concentration
of the dissolved gas in the liquid. A dynamic equilibrium has established at saturation
concentration. The solubility depends on the temperature of the liquid. When the temperature
increases, the solubility decreases [31][32].
In literature the solubility of radon in a liquid is often described by the Ostwald coefficient. The
Ostwald coefficient is defined as the volume of a gas dissolved at a given temperature and
pressure divided by the volume of the solvent at the same temperature and pressure [33].
Because radon is a trace gas, whose dissolved fraction does not alter the volume of the
solvent, the Ostwald coefficient L at a given temperature can be calculated by the ratio of the
radon activity concentrations given by the formula:
C
Rn,liquid
L =
, (1)
C
Rn
where the parameter is the activity concentration of dissolved radon in the liquid and
C
Rn,liquid
is the activity concentration of radon in air.
C
Rn
If the solvent is water, the dependence of the Ostwald coefficient L with the temperature of
water in Celsius (°C) can be expressed by [33]
T
H O
L = 0,105 + 0,403⋅ exp(− 0,0502 ⋅T )
, (2)
H O
The Ostwald coefficients for various organic solvents are given in Table A.5. The
measurement of radon in water using the methods of emanometry, gamma spectrometry and
liquid scintillation counting is described in the standard series ISO 13164 [33][34][35][36].

6.3 Radiological properties and radioactive equilibrium
238 232
In Table A.2 and Table A.3 the data for the natural decay chains
...