IONIZING RADIATION:
SOURCES AND BIOLOGICALEFFECTS
United Nations Scientific Committee
on the Effects of Atomic Radiation
1982 Report to the General Assembly, with annexes

UNITED NATIONSNew York, 1982

NOTE
The report of the Committee without its annexes appears as Official Records of the General Assembly, Thirtyseventh Session, Supplement No. 45 (A/37/45).
The designations employed and the presentation of material in this publication do not imply the expression of
any opinion whatsoever on the part oft he Secretariat of the United Nations concerning the legal status of any country,
territory. city or area, or of its authorities, or concerning the delimitation of its frontiers or boundaries.

UNITED NATIONS PUBLICATION
Sales No. E.82.IX.806300PANNEXD

Exposures to radon and thoron and their decay products

CONTENTSParagraphs

Paragraphs

INTRODUCTION ....................... .

I. GENERAL CONCEPTS AND PROPERTIES ............................ .
A.
B.
C.
D.

Physical and chemical properties ofradon and thoron ................ .
Measurement and identification ofradon and thoron and their decay
products ........................ .
Special quantities and units ........ .
Build-up and equilibrium ratios forradon and thoron daughters ........ .
1.
Attachment of radon andthoron daughters to aerosols ...
2.
Equilibrium factors for radon
and thoron daughters in ventilated confined spaces ........ .

JI. RADON AND THORON IN OUTDOOR AIR AND IN WATER ........ .

A.
B.
C.

D.
E.
F.

Sources ............•.........•..
Mechanisms of radon and thoron release ........................... .
Mechanisms of radon and thorontransport in the ground ........... .
Radon and thoron transfer throughsoil and emanation to air .......... .
Dispersion of radon and thoron in air
Dispersion of radon and thoron
daughters ....................... .

III. RADON AND THORON IN INDOORSPACE ............................. .

1-5

A.
B.
6-37

C.

6-9
10-11
12-16

D.

Sources ........................ .
Radon and thoron diffusion and exhalation ....................•••..
Radon and thoron dispersion in indoor
space .......................... .
1.
Indoor spaces other than tunnels ....................... .
2.
Tunnels ................... .
Equilibrium factor F in indoor air ... .

IV. EXPOSURE-DOSE RELATIONSHIPS
17-37

90-136
91-106107-113114-128
114-125
126-128
129-136
137-153

Inhalation ...................... .
Ingestion ...........•............

137-151
152-153

V. LEVELS AND DOSES ............... .

154-220

A.
B.

20-32

A.
B.
C.
D.

33-37

38-89
39-43

E.

44-46

Radon and thoron in outdoor air .... .
Radon in ~·ater •.•................
Radon in houses ................. .
Occupational exposures to radon andthoron daughters ................. .
l.
Uranium mines ............. .
2.
Non-uranium mines ......... .
3.
Other occupational exposures ..
Deliberate exposures to radon ...... .

154-156
157-164
165-204205-214205-209210-211212-214215-220

47-55

VI. ENERGYCONSERVATIONANDLEVELS OF RADON IN AIR ........ .

221-229

56-62
63-85

VII. SUMMARY ........................ .

230-234

86-89

References .............................. .

Page

Introduction
1. Radon and thoron are among the first of thenatural radioactive nuclides which were discovered,identilied and examined at the beginning of thiscentury. They are noble gases and are produced innature by the decay of the radium isotopes 226Ra and224Ra, respectively. Radium and its progeny have been

202

used for medical and technical purposes and forresearch for more than 70 years.
The interest of the Committee in radon and thoronlies in their detrimental effect on man. Since they occur
in nature, man has always been exposed, mainly
through inhalation of their decay products, to radon
and thoron daughters. The detrimental effect has been

2.

141

recognized since the sixteenth century, when miners incentral Europe suffered from what was then called"Schneebergkrankheit". Later experience of mining of
uranium in the middle of this century identified radon
daughters to be a source of cancer.
3. Man is everywhere exposed to radon and thoron
products. The major source or exposure consists ofradon and its decay products, occurring in domestic
housing. Radon emanates from building materials andfrom the ground below. In some countries the radiationdose to man caused by inhaled radon daughters constitutes more than 50% of the total radiation dose to manfrom other natural or artificial sources. Radon is also amajor problem in the nuclear fuel cycle because it gives
rise to an occupational exposure during uranium
mining and is a source of exposure to the public during
the storage of waste (tailings) from the milling of
uranium ore. Other sources of radon include theburning of coal, emissions from geothermal plants, andradon dissolved in water.
4. There are no epidemiological data available about
the effects of radon and thoron daughters on the public.
However, the detrimental effect of radon and its decay
products in indoor air can be estimated by extrapolation from information obtained from the exposure ofuranium miners. Although the estimates of exposure inthis case are far from perfect, they clearly demonstratethat high levels of radon and its daughters in air
warrant close attention. The Committee wishes to draw
particular attention to the fact that in a number ofcountries special efforts are now taken to conserve
energy by insulation of houses and by decreasing theventilation rate. It has been shown that such actions
cause increased concentrations of radon and radon
daughters in houses.

5.

The purpose of this Annex is to provide information about the levels and doses or radon and thoron
and their decay products and about physicalparameters influencing and causing these levels anddoses. The detrimental effects of radon and thoron
daughters are not dealt with in this Annex.

I.
A.

GENERAL CONCEPTS AND
PROPERTIESPHYSICAL AND CHEMICAL PROPERTIESOF RADON AND THORON

6. Radon (222Rn) and thoron (220Rn) are naturallyoccurring radioactive gases. Radon is produced by the
decay of 226Ra in the uranium series and decays byalpha particle emission to a polonium isotope (218Po)
which by further decay through isotopes of lead,bismuth, and polonium ends with a stable isotope oflead (206Pb). The half-lives and radiation energies areshown in Table I. Other physical data on radon arepresented in Table 2. Thoran is produced by the decayof 22 4 Ra in the thorium series and decays by alphaparticle emission to a polonium isotope (216Po) which
decays through isotopes of thallium, lead, bismuth andpolonium to a stable isotope of lead (208Pb), as shownin Table 1.
7. Radon and thoron are chemically inert, noble
gases. They occur in almost all materials and for themost part (90% and more) are trapped in the solids
carrying their precursors 226Ra and 224Ra. Accordingly,
the measurement of the gamma radiation emitted from142

the materials provides an indication or its uranium andthorium content as most of the gamma radiation fromthe 238U and 232Th series arises from the radon andthoron progeny.
8. Some or the radon and thoron may diffuse into
other media such as the surrounding water or air andfrequently the concentration of radon and thoron insurrounding water and air is higher than the concentration or 226Ra and 224Ra. Occasionally there may be a
deficiency of radon in water relative to 226Ra if thewater is in open contact with air so that the radon may
diffuse into air.
9. Because of the short half-life of thoron its concentration in water is generally insignificant, unless thewater has a high concentration of 224Ra. Radon can betransported a long way from its precursor and often
there is no simple correlation between the radon
concentration in air and water and the concentration of
226Ra in adjacent materials. However, radon concentrations in air in uranium mines and near mill tailings areusually well correlated to adjacent sources.
B.

MEASUREMENT AND IDENTIFICATION OF
RADON AND THORON AND THEIR DECAY
PRODUCTS.

10. Radon and thoron are identified by their radiationor their daughter products. In measurements of very
low activity concentrations in air (less than a few Bqm-3) radon and thoron can be concentrated or trapped,using activated charcoal filters at normal or low
temperature. At higher concentrations they can bedirectly collected and measured by ionization or scintillation methods (I1]. They can also be measured continuously by passing air through the measuring equipment.
In general the activity of radon and thoron in a sample
is monitored by measuring the number of emitted alphaparticles both from radon (thoron) and their progeny
which build up in the collected sample. Radon in water
is measured by gamma spectrometric methods directlyon the sample (including liquid scintillation methods)
or by measuring the radon released by bubbling a gas
through the sample. The activity or potential alphaenergy concentration (see paragraph 13) of daughters in
air can be determined by drawing air through a filter
and measuring the alpha particle activity with a ZnS or
silicon surface barrier detector, thermoluminescentdosimetry or track etch detector. Because of the shorthalf-lives of the radon daughters the measurement must
be made simultaneously with the collection or shortly
thereafter. Lead-212 and its decay products aremeasured some hours after collection following the
decay of the short-lived radon daughters.
11. After decay of the short-lived radon daughters thelong-lived isotopes of lead, bismuth and polonium
complete the uranium series. The practical use of theseisotopes as indicators of the current activity of radonand short-lived daughter products is limited. Even if themain part or 210pb in outdoor air comes from the decayof radon daughters in air, there is no simple correlation
between 210Pb and the local concentration of radon in
air. Similarly, 2l0Pb in water is not a reliable indicatorof earlier radon levels in the water because of variable
and unknown releases of radon from water to air
during its passage from the radium source to the wateroutlet, of insufficient time to allow significant decay ofradon in the water, of leaching of 210Pb from the rockand finally because of depletion of the daughters byadsorption on the rock surfaces. However, 210Pb in thehuman body (in bone) has been used as an indicator for
earlier inhalation of high concentrations of radon inmines [C8, H26].
C.

SPECIAL QUANTITIES AND UNITS

12. The potential alpha energy Epot.at of an atom in the
decay chain of radon or thoron is the total alpha energy
emitted during the decay of this atom to mipb or 208Pb,
respectively. The potential alpha energy per unit ofactivity (Bq) of a radionuclide j is Epo1,a11Aj where Aj isthe decay constant. Values of Epot,at and Epo1,a1/Aj arelisted in Table 3.
13. The potential alpha energy concentration of any
mixture of (short-lived) radon or thoron daughters in
air is the sum of the potential alpha energy of all
daughter atoms present per unit volume of air. The
usual unit for this quantity is MeV (-t. This unit isrelated to the SI units J and m3 according to 1 J m-3 =6.24 }09 MeV J-1. A special unit for this quantity used
for radiation protection purposes is the working level(WL). A WL is defined as a potential alpha energy
concentration of 1.3 10s MeV J-t of air. One WL corresponds approximately to the potential alpha energy
concentration of short-lived radon daughters in air
which are in radioactive equilibrium with a radon
concentration of 3.7 kBq m-3. For thoron daughters inradioactive equilibrium with thoron. one WL corresponds to a thoron concentration of 275 Bq m-3.
Quotients of potential alpha energy concentration (inWL) to activity concentration (in Bq m-3) are listed inTable 3 for the individual isotopes. The conversions
between the units used are as follows:

IJ= 6.24 1012 MeV
I MeV = 1.6 J0-13 J
I WL = 1.3 108 MeV m-3 = 2.08 J0-5 J m-3.
14. The equilibrium equivalent concentration ofradon or thoron, Xcq,Rn and Xcq,Tn, respectively, corresponding to a non-equilibrium mixture of short-lived
radon or thoron daughters in air, is that activity concentration of radon or thoron in radioactive equilibriumwith its short-lived daughters which has the samepotential alpha energy concentration Cpot as the actual
non-equilibrium mixture. The potential alpha energy
concentration of radon and thoron daughters inequilibrium with 1 Bq m-3 of radon and thoron is given
in Table 3. Accordingly. if the potential alpha energy
concentration is Cpot, the corresponding equilibrium
equivalent concentration for radon and thoron is
obtained as indicated in Table 4.
15. The equilibrium factor F is defined as the ratio of
the total potential alpha energy for the actual daughter
concentrations to the total potential alpha energy of thedaughters which would be in equilibrium with theradon or thoron concentration. Accordingly, Fis calculated from the ratio of equilibrium equivalent concentration of radon or thoron to the actual radon or thoron
concentration in air
Xcq RnF = --·- for radon
Xa,Rn

(I a)

Xcq, Tn
F = - - for thoron
Xa,Tn

(I b)

and

Sometimes the equilibrium factor for radon is assumed
to be known, and the value of Xcq,Rn is calculated bymultiplying the measured radon concentration Xa,Rn
by F.

16. The activity exposure of an individual to radon or
thoron is the time integral of the activity concentrationof radon or thoron, respectively, to which theindividual is exposed over a given time. The unit usedhere is Bq h m-3, The exposure to radon or thoron
daughters is expressed as "potential alpha energy
exposure" or ''radon or thoron daughter exposure", andis the time integral of the concentration (Cpot or Xcq,Rnor Xcq,Tn) of the daughter mixture to which theindividual is exposed over a given time. Potential alphaenergy exposure is expressed in the units:
I J h m-3 = 6.24 1012 MeV h m-3 = 4.8 104 WL h
I WL h. = 1.3 108 MeV h m-3 = 2.08 I0-5 J h m-3
Radon or thoron daughter exposure using the quantity
equilibrium equivalent concentration of radon or
thoron, respectively, is expressed in unit Bq h m-3. The
potential alpha energy exposure of miners is often
expressed in the unit Working Level Month (WLM).
One WLM corresponds to an exposure to a concentration of 1 WL for the reference period of 170 hours.
l WLM = 170 WL h = 2.2 1010 MeV h m-3 == 3.5 l0-3 J h m-3
I J h m-3 = 285 WLM
One WL corresponds to an equilibrium equivalentconcentration of radon (Xcq,Rn) of 3700 Bq m-3 and apotential alpha energy exposure of 1 WLM radon
daughter corresponds to a radon daughter exposure of
6.3 JOS Bq h m-3. For thoron daughters 1 WL corresponds to a Xcq,Tn value of 275 Bq m-3 and 1 WLM
corresponds to 4.7 104 Bq h m-3.

D.

BUILD-UP AND EQUILIBRIUM RATIOS FOR
RADON AND THORON DAUGHTERS

17. The build-up of radon or thoron activity is givenby the expression(2)
where A(t) is the activity of radon or thoron containedin a confined unventilated space at time t (at time t = 0
the activity is assumed to be zero), Fr is the emanating
power which is the fraction of radon or thoron released
into that space from the 226Ra or 22 4 Ra source ofactivity A0 , and 11. is the decay constant for radon or
thoron. The activity concentration in a confined unventilated space increases according to the same formula
divided by the volume V of the space. If the space isventilated with ventilation rate Av the increase of radonor thoron concentration follows the expression

where Xa(t) is the act1v1ty concentration of radon or
thoron in air, and A.v is the ventilation rate defined as
the number of air changes per unit time (h-1), which is
the quotient of the air flow rate (m3 h-1) through thespace and its volume (m3). The build-up for radon isshown in Figure I for several values of /1.v. Because of
the short half-life of thoron the equilibrium level of
143

E
a
z
::>

oom coc

7

~ 5

....<

~
z

"'
~

'

0""'
OOO

~v = 0,25 h" 1

3

8[][IO;>z2~v" o.s n1

<
"'

1

~.1i; 1

0
0

0

6

12

2,

18

JO

36

,2

Figure I. The relative growth of radon concentration
In a confined space as a percentage of theequlllbrlum value for no ventilation versus time fordifferent ventilation rates Xv (h-') (W14][C17]

thoron is reached within 5 minutes and in practice isindependent of the ventilation rate (assuming Av < 10h-1).
18. Radon and thoron emanating into the air arepractically free of decay products so that the daughter
activity in air builds up with time. The build-up ofdaughter activity concentration in a volume of air
containing a given radon or thoron activity concentration (the value of which is only affected by decay) is
given by the following general expression= Xa (0)±Gi e- Ajt

where Xa,j is the activity concentration of daughter j in
air and Xa is the activity concentration of radon or
thoron in air. It is assumed that factors influencing theconcentration of radon or thoron daughters in air otherthan radioactive decay and ventilation rate can bedisregarded and that there is a constant emission ofradon or thoron into the ventilated space. The corresponding decrease of potential alpha energy concentration is estimated by multiplying the activity concentration of each daughter by the respective potentialalpha energy as given in Table 3 and taking the sum ofthese products.

i-0

where

1.

j

n Ak
Gi=.

(n,;,i)

k-l

J

(4)

n (1.n - 1.;)n-0

Xa(O) is the radon or thoron activity concentration attime t = 0, and A represents a decay constant. Values of
j = 1.2,3, etc. stand for the first, second, third etc. radonor thoron daughter, while i = 0 represents the parent
radon or thoron. By multiplying the relative activity ofthe daughters by their potential alpha energy, the corresponding growth of the potential alpha energy of theradon daughters can be estimated. This is shown in
Figure 11 for a constant radon concentration. The
increase of the potential alpha energy concentration
Cpot during the first 40 minutes is given approximately
by [E6]

Cpo1 (t) = Cpo1 (t1)(ti"t)

0.85(5)where t1 is one minute.
19. It can be seen from equation (3) that the activity
concentration of radon decreases as the ventilation rateincrease_s, while the concentration of thoron is approximately independent of the ventilation rate (assuming
A.v < 10 h-1). The corresponding decrease of the activity
concentration of the daughters can be estimated fromthe expression
Xa .
j_.J = n - - (6)

Xa

n-1

+ A,v
An

144

...

Figure II. Potential alpha energy
concentration for an lnltlally puresource of 222 Rn and the relative
contributions to It from theprogeny, as a function of time

TIME Chl

Xa,j (t),0TrHE (S)L8

Attachment of radon and thoron daughters toaerosols;O. At the ti~e of formation of the first daughter,.18Po or 216Po ts an unattached, predominantly (morethan 90% [D5]) positive small ion or neutral atom (sizeof the order of 10-3 µm). Some ions may be attached tomolecules of water vapour and other gases. After a timeof the order of 10-100 s the daughters will attach to anaerosol particle (normal size in the range 10-2-1 µm). In
the subsequent alpha decays the radioactive atom orion may again become unattached because of the recoil~nergy when it decays. For example, the recoil energy
m the decay of 218Po (117 keV) is transferred to its
daughter 214Pb. Lead-214 will desorb, and appear as an
unattached ion or neutral atom for a short time after its
formation. but then becomes attached. This recoil effecthas been found to apply to about 80% of the decays of
218 Po [M13]. The first decay product of thoron is 216Po
which is very short-lived (T112 = 0.15 s) and therefor~
unat!ached. The next decay product, 212Pb, has arelatively long half-life (T112 = 10.64 h) and therefore
in room air it is predominantly attached.
21. Changes in the air concentration of the various
radon and thoron daughters are governed by radon andthoron exhalation rate, radioactive decay, attachment
and recombination, deposition and sedimentation, andtransport by diffusion and air flow.
22. The attachment of radon or thoron daughters toaerosols depends on the diffusion coefficient of freeions and atoms and on the concentration and particle
size distribution of the aerosol. The attachment toaerosols has been studied by several investigators [L6,

82. 811, D8, K5. R2. W5]. The attachment rate can be
expressed by"'
A.a = X \ K (Li, r) n (r) dr(7)0

where x is the number of particles per unit volume ofair: 6. is the diffusion coefficient of free atoms in air;n(r)dr is the relative number of particles in an
increment (dr) of radius at the radius r; K( 6. ,r) = 4 n r2
L:,,. h(l + hr); h = v/4 6.: v is the mean gas kinetic
velocity of free daughter atoms ( = 1.7 ]04 cm s-• at
2ooq (JI].
23. If one assumes that the aerosol distributionindoors and outdoors is log-normal with a CountMedian Aerodynamic Diameter (CMAD) of 0.05 µm
and a geometric standard deviation of 3, and if one
adopts representative values of 104 cm-3 for particle
density and 0.054 cm2 s-1 for !:,,. , then the calculated
attachment rate i..a is about 10-2 s-1, corresponding to amean life of the unattached radioactive ion of about
100 s. For working rooms or rooms with smokers, theconditions will be different. In a mine, for example.
with CMAD = 0.1 µm and x = 105 cm-3, theattachment rate will be 0.28 s-1 and a corresponding
mean life of only about 4 s. The mean lives of free ionsand the correlation between the concentration of freeions and aerosols have been studied repeatedly [D8,K5, R3].
24. The deposition of attached daughters to surfaces isdetermined by the diffusion of their carrier aerosols
and by the quotient of the surface area S to the volume
V of the room containing the aerosols. The deposition
rate Ad is given by the expression

about 0.007 cm2 s-• (at a concentration of 5 104 cm-3).
These experiments were made in an aerosol-free atmosphere. In other experiments [PIO), the diffusion coefficient of positively charged decay products of thoron
has been measured under very dry conditions (relative
humidity 2%) to be 0.048 ± 0.003 cm2 s-1 and with highrelative humidity (30-90%) to be 0.068 ± 0.004 cm2 s-1.
For neutral 212pb atoms the diffusion coefficient was
0.067 ± 0.004 cm2 s-1, irrespective of the humidity.
26. A study concerning the effects of charge. humidity
and the number of condensation nuclei on radon
daughter concentration in air has been made by Cooper
et al. [ClOJ. The study laid particular emphasis uponuranium mines and showed great variations of theaerosol attachment and surface attachment (plateout)
rates. The effect of humidity on the diffusion coefficientof radon daughters is dubious, although there seems tobe agreement that the plateout effect strongly depends
on the 'fraction of daughters which are not attached toparticles [C9, Ml l]. The effect of turbulent air in mine
environments has been found to lead to a reduction of
the airborne radon daughters [W13, S9] owing to anincreased plateout on the walls or plateout on the fan
blades. The fraction of radon daughters which attaches
to the blades of a fan that circulates the air issubstantial if the relative humidity is low (5%) andnegligible when the relative humidity is high (80%)[H14]. The effects under conditions of low humidity areillustrated in Figure III. Similar effects were also

"',_
§

(8)

w

>

,_

where Vd is the deposition velocity (m s-1). The value of
Vd for the attached daughters depends on the size
distribution of the carrier aerosols and normally lies
within the range of 10-s to lQ-4 m s-•. For unattacheddaughters the value of Vd lies in the range of J0-3 to 10-2
m s-1 [Jl. A9]. For particles with normal Activity
Median Aerodynamic Diameter (AMAD). i.e., 0.05-0.2µm, a deposition velocity of 1()-4 m s-1 and S/V quotientof about 2 m-1 (which is a "normal" value for rooms),
the deposition rate is about 0.7 h-1 [Jl] and the mean life
is accordingly about 1.4 h. For unattached daughters
the deposition rate is of the order of 1 min-1.
25. The diffusion coefficient of the unattached decay
products of radon and thoron in air is of the order of
0.05 cm2 s-1. Various values have been used within therange of 0.034-0.06 cm2 s-1 [C5. D6, K 11]. Decreasing
diffusion coefficient with increasing humidity has beenreported [Rl] and may be due to clustering of thedaughters or clustering of water molecules on daughter
atoms [Kl 1] in the air, which is not absolutely free ofcondensation nuclei (size in the range 0.01-0.1 µm).
Theoretical studies on the mechanism of the interactionof radon daughters and water vapour are presented in[H23]. If the concentration of condensation nuclei isvery low and constant but the relative humidity changes
from 5 to 90%, the diffusion coefficient for unattachedthoron daughters is found to remain fairly constant(0.05-0.06 cm2 s-1) [KlO]. The diffusion coefficient isalso independent of thoron concentration in thereported range of 70-4000 kBq m-3, However. if theconcentration of condensation nuclei increases several
orders of magnitude (e.g., by decreasing the ventilation
rate in a room) the diffusion coefficient decreases to

:'.3

w

"'

....

:::
"
TIME (h)Figure Ill. Radon daughter concentration
In the air (curve 1, full scale 10 WL), on
the
wells
(curve 2,
full
scale
1000 counts/mln), and on the fan(curve 3, full scale 3000 counts/30 mln)
In response to the switching on and off
the fen. Curve 4 (full scale 10• cm- 1 ),the condensation nuclei concentration,and curve 5 (full scale 70 kBq m· 1 ), theradon concentration, are practically
Independent of the fen being on or off.
Humidity was < 5% [H14]

studied in room air [J12] and from preliminary results it
was concluded that the removal by a fan system mainly
affected 218Po. In experiments with monodisperse
aerosols (diameters 2-10 µm) and radon and radon
daughters the attachment rate of 218Po was studied[Hl 1]. It was concluded that the attachment rate wasproportional to particle concentration and particle
cross-section area, which implies that the attachment
process of 21spo to aerosols can be described by gas
kinetic theory. The attachment rate was also found to
be proportional to the radon or 21spo concentration.
27. The equation governing the fraction of unattachedradon or thoron daughters in a room involves terms forradioactive decay, attachment, deposition of aerosols
and ventilation. Assuming that the outdoor concen145

tration can be neglected. the fraction of unattached
218Po and 212Pb atoms is given by

I

Frd =
I+

(9)

A.a

A.1 + Av+ Ad

where A.a is the rate of attachment of free daughter
atoms to aerosol particles; A.1 is the decay constant; Avis
the ventilation rate: Ad is the wall deposition rate forattached daughter atoms [JI]: and Frd is the quotient of
the number of unattached 218Po or 212Pb atoms to thetotal number of 2111Po or 212Pb atoms, respectively.
Sometimes a fraction F'rd is given which is the ratio of
the number of unattached 21BPo or 212Pb atoms to thenumber of 21BPo or 212Pb atoms assumed to be in
equilibrium with radon or thoron, respectively. This
fraction corresponds to Frd F1, where F1 is the activity
equilibrium ratio of 21spo or 212Pb to radon or thoron,
respectively; i.e., F'rd = Frd F1.

28. With the typical value of Ad given above(paragraph 24), it is obvious that for daughters with ahigh decay constant like 21BPo, )..1 will be the mostsignificant term in the above equation (9) for a given
value of A.a, while the ventilation rate Av within a normal
range (0-1 h-1 in buildings) will be less significant.
However, in mines with high ventilation rates the valueof Av will significantly influence the value of Frd forradon daughters. As increased ventilation may cause adecrease of the aerosol concentration, the value of A.awill decrease, with an increase in the fraction of unattached radon daughters.

29. Measur1cd values of Frd and F1 in thorium plants[M16] are Frd = (0.74 ± 0.02)% and F1 = (3.7 ± 2.5)%(= 212Pb/Tn), giving F'rd = 0.027 ± 0.021 [K11].
Several values of the fraction of unattached radon
daughters have been reported. In Sutton, in the United
Kingdom, Frd for 21spo varied between 0.07 and 0.40
(relative to 21sro with no consistent difference indoors
and outdoors [D7]). In New York City, F'rd (unattachedfraction relative to radon) varied in two series between
0.01 and 0.06 (average 0.04) and 0.05-0.12 (average0.09) [F3]. In Sterling Forest, Frd for 218Po was measured
to be 0.04-0.1 (average 0.08) [G4] with the lowest value
occurring on a rainy day. F'rd for 21spo indoors in New
York has been measured to be 0.04-0.07 {F3, G4].
30. The fraction Frd of unattached 2tBpo atoms has
been measured [D8] in open air and in mines as afunction of the concentration Xa of condensation nuclei
in the a1r. The measured values were compared with thetheoretical expression

F -A1
rd - A1 + k Xa

(10)where l1 is the decay constant for 218Po and k Xa = J..a.
The values of k have been calculated by Jacobi and byRaabe to be 6 10-s min-1 cm3 and 4 10-s min-1 cm3
respectively [08]. The comparison with experimentai
values is presented in Figure IV [D8].

Frd
l·O

O·!I
0·8

Xa oo• c,,.-•i
Figure IV. Variation of the fraction of unattached 211Po as a function of theconcentration of condensation nuclei. ~ - Tin mine; • - Colley HIii
(rural), 0 - Sutton (suburban); • - artlflclal atmosphere [DB]31. Activity concentrations of attached and unattached radon decay products in mines have beenmeasured [R3] and the fraction Frd (unattachedactivity/total activity of respective daughter) has been
calculated for 218Po, 21 4 Pb and 214Bi [M12]. In 60
samples, mean and standard deviation for Frd wereobtained of (8 ± 10)% (range 0.3-55.4%) for 218Po, (4.9
± 6.8)% (range 0.06-31.4%) for 214Pb and (2.7 ± 3.8)%(range 0.08-16.4%) for 214Bi.

32.

In summary, the rate of attachment of radon andthoron daughters to aerosols normally lies in the range
10-1-10-2 s-t, with higher values in dusty air. The rate ofdeposition (plateout) on indoor surfaces is about l h- 1
for attached daughters, and I min-1 for unattacheddaughters. Low humidity and increased air turbulence
increase the plateout. The unattached fraction of radon
and thoron daughters is normally in the range 1-10%.
The unattached fraction increases with decreasing
aerosol concentration and with increasing ventilation
rate.
146

2.

Equilibrium factors for radon and thoron daughtersin ventilated confined spaces

33. The daughter ratios given by equation (6) may be
combined with the conversion coefficients of Table 3 toobtain the equilibrium factor F as a function of ventilation rate. These are presented in Table 5. Corresponding values for the potential alpha energy concentration of the daughters can be derived by multiplying
F by the potential alpha energy concentration of thedaughters if they were in equilibrium with the parent
radon or thoron activity concentration Xa· The potentialalpha energy concentration for radon daughters calculated in this way is shown in Figure V as a function ofventilation rate [PI 2]. This calculation assumes noplateout, and negligible daughter concentration in theinlet air. For thoron daughters, the corresponding
quantity simply follows the equilibrium factor F, as thethoron activity is fairly constant.

,oPARAMETER

l =
2 =
3 =

.,,
~

_.

RV (Dq m- 3 s- 1 1 (Radon)

o·•

0.8

<

>

l 10::
2 10_45 10

4 10 10::=5 •20 10_4

6 =~o 10_,1
7 = 100 10

UJ>

5 .,.,
w

a:

0
"'
::;

0,6

~

"'2
.,
"'

::;

0~

s

2"~ O

~

Al R CHANGES PER HOUR

Figure V. Potential alpha energy
concentration of radon daughters
as a function of ventilation rate

7

0.2

[P12)

34. When the effects of plateout and radon daughtersin the inlet air are included, the simple description
given above no longer applies. The degree of plateout
to the walls is strongly influenced by the unattachedfraction, which in turn affects the activity ratios and theequilibrium factor F. The equilibrium factor for radon
daughters has been estimated from measurements madeunder varying aerosol conditions [W14] and the results
are shown in Figure VI. It is apparent that average
3
3
AEROSOL CONCENTRATION, 10 CM-

MEASUREMENTS WITH SMOKE\ . ,........-.

. ..: /7

0.6
MEASUREME•HSWITHOUT SMOKE _~/§/ x •

x

:,:
::::,

"'
m 0.4
~

s0

"'

I~""':~~ .,.

•,

/

0.2

Ad= 30 h-1

Ad= 0.2 h-1Figure VII. Equlllbrlum factor for radon daughters In aroom as a function of ventilation rate >..,, with varying
emanation rates Into a room and the radon daughter
concentration In outdoor air taken Into account(attached daughters)

050

for outdoor air, with an equilibrium factor of 0.75. Inother theoretical calculations [Jl] the equilibrium factor
has been estimated to be as low as 0.2 for conditions of
low aerosol concentration (A.a = 100 h-1) and a ventilation rate of A.v = 1 h-1, However, when allowance ismade for the equilibrium factor for inlet air drawn fromoutdoors, the equilibrium factor increases to greaterthan 0.3 (calculated from [P9) for the reference housedescribed in paragraph 105). For rooms with highaerosol concentrations (A.a > 1000 h-l) the equilibrium
factor F will be larger (with A.v = 1 h-1, F = 0.35,
according to [J1)). These results suggest that approximate estimates of F. which take plateout into accountmay be obtained by multiplying the values of F in
Table 5 by 0.4 (A.a = 100 h-l) or 0.6 (A.a = 1000 h-1) forA.v < 2 h-1 or by 0.5 if A.a is unknown.

(unattached daughters)

AV= 0.1 h-l

10

AV (h-l)\00

0.8"'....0u

VENTILATION RATE

[W14]

10

"'

0 .......~.................L.J....._L.L.........................._._,._.__._,__.L.I....L.J....L.J..J
0.0
0,5
2,5
1.0
1.5
2fJ
3.0

500

100

ATTACHMENT RATE

Aa

35. The effect of deposition on the walls (plateout) inradon daughter ratios in uranium mine atmospheres
has recently been studied [H21]. It was concluded that
selective plateout, particularly of 218Po, is the main
reason why it is impossible to find simple correlations
between activity or potential energy concentrations andventilation rate or age of the air.

(h-l}Figure VI. Equlllbrlum factor for radon daughters In a room
as a function of the aerosol concentration and theattachment rate 1'.0 • The emanation rate Into the room Is
7.4 Bq m-• h- 1 [W14]values of F corresponding to different values of the rateof attachment A.a agree reasonably with the theoreticalcurve which includes the effect of plateout. Significant
concentrations of radon daughters in the inlet air
complicate the situation further. Figure VII illustrates
the variation in the equilibrium factor F with ventilation rate for a number of exhalation coefficients R,(Bq m-J s-l) defined as the exhalation rate R (Bq m-2s-l), multiplied by the quotient S/V (m-1) of surface
area to volume .. For this calculation an equivalentequilibrium concentration of 2.6 Bq m-J was assumed

36. Plateout also influences the factor F for thoron
daughters. In rooms with low aerosol concentration
and a ventilation rate of about 1 h-l, F is about 0.009,
instead of 0.058 as given in Table 5. In rooms withhigher aerosol concentration Fis about 0.013 [Jl]. Other
calculations show somewhat higher values [W14]. It
seems appropriate therefore to assume that theequilibrium factor is generally less than half of thevalues given in Table 5.
37. If there is a ventilation system with recirculationof part of the air and also air filtration, there will be adecrease in the radon concentration proportional to thefraction of fresh air admitted (if the radon concentration in fresh air is neglected). However, if the air
exchange rate, including recirculation, is unchanged,
147

the equilibrium factor F will not change, unless there isa decrease in the aerosol concentration because of recirculation.

II.

RADON AND THORON IN OUTDOOR
AIR AND IN WATER

38. The concentrations of radon and thoron and of
their daughters vary substantially with time and space.
In general. the activity levels in air make a much moresignificant contribution to radiation exposure thanthose in water. The levels of radon and thoron in air orwater depend on four factors. These are the nature of
the source, its emanating power, transport of radon andthoron from the source and their ultimate dispersal.
These factors will be considered in this chapter.
A.

SOURCES

39. Radium and thorium in soil are the main sourcesof radon and thoron in the global atmosphere. Both theradium and thorium concentrations usually lie in therange of 10-50 Bq kg-I (Annex B). The averageworld-wide concentration of both elements in soil isassumed to be 25 Bq kg-I (Annex B). In seawater theconcentration of 226Ra is 4 to 5 orders of magnitude
lower [825], and the concentration of 228Th is 6 to 7
orders of magnitude lower [M27]. Nevertheless, forreasons which are discussed in paragraph 62, the exhalation rate from the oceans is only about 2 orders ofmagnitude lower than that for soil. Some publishedvalues of radon exhalation rates per unit area are listed
in Table 6 [W15]. The estimated area-weighted averageradon exhalation rate per unit area from soil, excluding
Antarctica and the Greenland ice cap, is 16 mBq m-2 s-1[Wl 5] corresponding to a total exhalation rate of 1.9
1012 Bq s-1. The values reported in Table 6 have a lognormal distribution with a geometric mean of about
two-thirds of the arithmetic mean. In a study on theflow of 210Pb into the global atmosphere good
agreement has been achieved between calculations
based on the geometric mean of the radon exhalation
rates per unit area and those based on glacier ice
concentrations of 21opb [JI 6]. Other estimates ofworld-wide average soil radon exhalation rates per unit
area are 15 mBq m-2 s-1 (17] and 19 mBq m-2 s-t [B13].
Reported ranges are 0.2-70 mBq m-2 s-1 [Wt 5, Gl 7].
The total annual radon exhalation is then 5-10 1019 Bq,
corresponding to a total equilibrium activity of theorder of 1018 Bq. As may be seen in Table 23, theconcentration of 222Rn in ground level air varies widelywith geographical location, and is up to two orders ofmagnitude higher over land masses than in maritime
locations. Other sources of radon in air are plants andground water ( < }019 Bq a-1), natural gas (about 1014
Bq a-t) and the combustion of coal (about 1013 Bq a-1)
[H7]. Radon from houses may contribute about 1016 Bq
a-t (assuming 109 reference houses of the type presented
in Table 13, the true value may be between 5 101L1Q17
Bq a-1). The total annual radon release from uranium
mines, mills and tailings is of the order of 1015 Bq(assuming 120 GW(e) installed nuclear capacity and anormalized radon release of 2 1013 Bq [GW(e) aJ-1) (seeTable 2 of Annex F).
40. Geothermal power stations are a source of radon
which is minor from a global perspective but may be of
local significance. At present only a small part of theworld energy requirement is produced from geothermal
sources (0.1 %) [US] but increases in the future are148

possible. The production of hot steam in deep
geological formations leads to releases of radon fromwater in the bed rock. Measurements performed in Italy[M4] indicate a radon release per unit energy generated
of about 4 1014 Bq (GW a)-I, which is three to fourorders of magnitude higher than the normalized releasefrom coal-fired plants. The radon concentration in
geothermal steam at Wairakei and Broadland in New
Zealand is 100-400 Bq kg-I steam which results in anannual radon release of 101 t to 1012 Bq.
41. Another source of interest is phosphate mtntng.
Rock phosphate is used mainly as a source ofphosphorus for fertilizers. Morocco, the Soviet Unionand the United States are the main producers. The
United States produces 40% of the total world
production of phosphate rock and more than 80% of
the total United States production occurs in Central
Florida. Sedimentary phosphate ores such as those in
Morocco and Florida often have a higher concentrationof uranium and its decay products than magmatic ores
such as those from Kola. Most phosphate is mined in
an open-pit or strip-mining process. In order to reachthe phosphate rock, the overburden and a second layer
called the leach zone have to be removed. The leachzone has generally a higher concentration of 226Ra thanthe overburden and is afterwards frequently placed ator near the surface, resulting in increased 226Ra concentrations [Cl 7]. The subsequent radon exhalation ratefrom phosphate regions depends on land reclamation
practices. A quantitative characterization is given in
Figure VIII, which refers to phosphate regions in
Florida [R8].
SOIL CORE RAOIUM

UntltPr1d
Tllillngs
OvtrbtJtden

0.01

...

SOIL CORE AA.C>IUM. • IQ •i

1

RADO!/ EMANATION
Taillnga
Ovcrbutdfr, - - - - - - - - - - - -

Dd>M

0.01

...
RADON EMANATION RATE (Sq m- 2 s-1)

Figure VIII. Radlologlcal charecterlstlca of Polk County
lands, Florido (geometric means end ranges by landtype) [RB]42. Volcanic activity as a source of radon in air has
been investigated in Iceland, Japan and Hawaii (W16,814, 18]. Radon concentrations in the volcanic plumes
were observed to be above ambient air concentrations
and in Hawaii concentrations of the order of 50 Bq m-3
were reported. The radon release rate was estimated to
be of the order of 10 GBq h-1 which is negligible
compared with the radon release rate from the island
surface. The radon release from the eruption of Mount
St. Helens in the United States on 19 May 1980 has
been estimated to be about 1011 Bq of radon in theplume [F6], which corresponds to about 10% of the total
atmospheric inventory. However, this estimate has notbeen confirmed by other observers.

43. Radium-224 in soil is the main source of outdoor
thoron. However, because of the relatively shorthalf-life of 224Ra (3.7 d) it must be continuously
supported by its precursors. Thus, in practice, 228Th(T112 1.9 a) and 228Ra (T112 5.8 a) control the thoron
exhalation rate. Even though the activity exhalation
rate for thoron is much higher (about 100 times) [B 13,
H7] than that for radon. the total global activity
inventory in the atmosphere is much less (about 100
times less) than that for radon, primarily because of theshorter half-life of thoron.
B.

MECHANISMS OF RADON AND THORONRELEASE

44. The physical process of the radon and thoron
release from the structure of the rocks is not yet fully
understood. Only a part of the radon and thoron atoms
produced by decay in a particle is released to thesourrounding water or air. The fraction of the radon or
thoron atoms formed in a solid which makes its way
into the pores of the medium, and thereby becomesamenable to transport, is defined as the emanating
power of the solid for radon or thoron. Somemechanisms describing the release of radon are
reviewed in [A2, T6].
45. The transport and release of radon and thoron
from a solid into air or water occurs through diffusionand flow of the air or water. High porosity increases the
diffusion rate. In a very dry solid the release of radonor thoron is reduced by readsorption of radon andthoron atoms on surfaces in the pores and fractures inthe solid. If the solid is slightly moist, the radon andthoron release is enhanced up to a certain moisture
content, above which it decreases again because of thelower diffusion rate in water-filled pores [MlOJ.
46. The exhalation of radon per unit area for large
particles and pieces of uranium ore has been demonstrated to increase with the size of the particles [T4].
This effect may be due to the presence of microfracturing in the samples. Similarly, the exhalation ofradon from ordinary rock samples may be less than theexhalation from rock walls in a mine, because of
greater fracturing and the presence of cracks in thewalls caused by blasting [L9, K7]. Table 7 shows theresults of some measurements of radon exhalation fromcore material and a surface in a mine [L9].
C.

MECHANISMS OF RADON AND THORON
TRANSPORT IN THE GROUND

47. Once radon and thoron have entered thesurrounding water or air phase, they are further transported by diffusion, mechanical and convective flow.
and by percolation. The diffusion process can be
expressed by the formulax(x)~ x(o) exp ( - x /l/¥)less [Tl]. This means that radon will have decayed to
10% of its original value after a diffusion through 5 mof air, 5 cm of water and about 2 m in soil. Migration ofradon for much longer distances by diffusion is notimportant. Accordingly, the transport of radon overgreater distances in water and air must occur throughother mechanisms. The short half-life of thoron (55 s)
limits its migration to less than one per cent of that ofradon [J2). Therefore, the remainder of this discussion
relates mainly to radon.

48. Radon in rock or soil may also be transported bymechanical forces in the earth causing changes of porespace through compressive stresses. These may becaused by earth tides or by intermittent forces such as
those of earthquakes. Such mechanisms may explainintermittent variations in radon exhalation from soil
surfaces.
49. Another possible transport mechanism · isthermally-induced fluid convection. Some data suggestthat this process may be important, but further results
are needed [M14].
SO. In the main, however, the transport of radon
though soil and bedrock by water probably depends on
the percolation of water through the pores and along
fracture planes of the bedrock. The radon concentration in water from a percolation zone Xw,Rn is related
to the radium concentration. of the percolated rockCroclr.,Ra, the rock density, Prock. the emanating power.
Fr, the fractional pore space of the rock (porosity).
Frock,ps, and the water velocity v, through the formula
Xw,Rn ( X ) =Fr Prock Crock. Ra ( l _ e- WV\
J
F,ock, ps(12)

where A is the decay constant and x is the distancewhich water travels through the rock (A2]. It follows
from this formula that heavy rainfall causes a decreasein radon concentration as the velocity v increases. Thus.
if the water in a well is supplied by water from a percolation zone of higher than normal radium content, theradon concentration in the well is likely to decrease
after rainfall. However, if the percolation water is aminor source for the well, heavy rainfall might flush out
radon-rich water from the percolation zone thereby
causing an increase of radon concentration. Variationsof radon concentration in well water are sometimes
observed to be seasonal [A2, K8, Sl 1].
51. The radon content in ground water and water insprings and wells is seen from equation (12) to dependon the radium concentration in the rock of the aquifer.
Consequently, the highest radon concentrations arefound in water in the vicinity of uranium ore bodies.
High concentrations(> 400 kBq m-3) are also found inwells bored in granite, pegmatite, syenite and porphyry.
Low radon concentrations occur in ground water frombasic rocks and sedimentary rocks, such as limestoneand sandstone [K8J.

(Ill

where x(x) is the radon or thoron concentration at
distance x in water or air from the surface; x(o) is theradon or thoron concentration at the surface; ~lr. is theeffective diffusion coefficient and A is the decay
constant fG8J. The diffusion coefficient ll 1r. for radon isabout 0.1 cm2 s-1 in air and 10-s cm2 s-1 in surface water[Tl]. In soil ll 1r. is usually of the order of 10-2 cm2 s-1 or

52. In investigations of radon in ground water in six
counties in Maine, United States, the highest concentrations were found in granites and adjacent sedimentaryrocks which have experienced great metamorphic
change. Low concentrations were found in groundwater from non-granitic areas with little metamorphic
change. The average radon concentration in groundwater in granite zones was about 1 MBq m-3 and inchlorite zones 40 kBq m-3 [HlOJ.
149

53. The radon concentration in water may vary withthe depth of the wells if the size of the percolation zone
depends on the well depth. This effect has been foundto be significant for wells in granite up to depths ofaround 50 m, as can be seen in Figure IX. At depths
10'4.

..
.
,,

..,
'E
c-

.,,
a,

fl

•"

,,••
•
A,•R
/~ ' •
,,··

10"'

z:

.

,,

•

~

,-

<
~
~

/\ I\

u

a
u

10'

~
,u
<:

"'

.

"

0 Cumbi:rland
CJ H.1nccckt:,.

IXn, Rn (z)Jsoil =Fr Xsoil, RaF
soil, ps

• Penob1e:0t

10

(14)

• Waldo... Yori<
0

50

JOO

150

200

WELL DEPTH (m)Figure IX. The variation of 222 Rn concentration
as a function of water well depth In granites[H10]beyond 100 m there was a tendency for radon concentrations to decrease [HlO]. In other investigations no
significant correlation of radon concentration withdepth has been observed [S11).
54. Measurements of radon in soils can be used inuranium exploration, particularly when the uranium
ore is covered by a thick layer of soil (more than about
0.5 m) [D9], although anomalies arising from selective
radium or radon transport from the uranium ore may
give rise to errors in interpretation. Meteorologicalfactors, particularly those affecting the moisture
content of the soil, can result in large variations inradon concentration in the soil [U6, Cl].

55.

Radon measurements in sub-surface waters and indry boreholes have recently been used as an earthquake
predictor [SlO, S37, S38, K16, Nl]. It is postulated thatdilation of the rock caused by strain releases radon to
the ground water and subsequently increases the radon
content in well and spring waters in the vicinity. Thismethod is however subject to many complicating
factors and there is still considerable doubt about its
practical applicability.

D. RADON AND THORON TRANSFER
THROUGH SOIL AND EMANATION TO AIR
56. Radon and thoron enter the air contained in soil
by diffusion from soil particles or sometimes fromradon-rich ground water at greater depths. The concentration of radon and thoron in this air decreases withdecreasing distance from the surface because the gases
escape to the open air above the ground. As the exhalation increases, the gas concentration in soil air
decreases, and vice-versa.
57. The diffusion mechanisms for radon and thoron
are the same. For radon, the diffusion through soil tosurface can be expressed by the diffusion equation [J2]
150

(13)

soil, psl>. Lincoln

5
<

•

••

!:;

0

L1
:-11

>-

+ Fr ARnX,oil, Ra _ A X(z)FRn a, Rnwhere Xa,Rn(Z) is the concentration (per unit volume ofsoil air) of radon atoms at depth z (z=O at the groundsurface); ~ k is the effective diffusion coefficient (cm2s-1); Fr is the emanating power (0 < Fr< 1); A.Ra and
ARn are the decay constants of radium and radon,
respectively; Xsoil,Ra is the concentration (per unit
volume of soil) of radium atoms; and Fsoil,ps is theporosity of the soil. Under steady state conditions
dXa,Rn(i)/ dt = 0, and the concentration of radon
activity at depth z is given by.
•dXa, Rn (z) = t'!i d 2Xa, Rn (z) +
dt
k
dz 2

where [Xa,Rn(z)]soil is the radon act1V1ty concentration
per unit volume of soil air at depth z; Xsoil,Ra is theradium activity concentration per unit volume of soil.
58. At great depths (z -,. co) the equilibrium radon
concentration in soil air is
Fr 'Xsoil, Ra

Fsoil, ps
For an infinitely thick soil, the exhalation rate is given
by

z=O

(15)

where .b.ert( = Fsoil,ps 4) is the effective bulk diffusion
coefficient. The combination of equations (14) and (15)
gives

V

R = ARn Fr Xsoil, Ra t'!ik/ARn(16)

The rate of diffusion is highly dependent on the
moisture content of the soil and the diffusion coefficient ( 6 cff) can vary by several orders of magnitude. A
value of 5 10-2 cm2 s-1 for ~ k has been suggested as
typical for soil [S39]. Assuming that Fr = 0.1, Xsoil,Ra =0.074 Bq cm-3 and ~ k = 0.05 cm2 s-1,
R = 2.4 10- 2 Bq m- 2 s-1

which compares reasonably with measured averagevalues of 1.5-2.0 10-2 Bq m-2 s-1. The corresponding
value for thoron is 1.9 Bq m-2 s-1 if all constants except
t are the same. Several studies of thoron exhalation
have been reported [D4; G16, Ml, MIO, S40] and theaverage observed value of the thoron exhalation ratefrom soil is around 1 Bq m-2 s-t (J2].
59. The concentration of radon and thoron in soil air
is affected by meteorological factors each as barometricpressure, humidity, rainfall and temperature. Risingbarometric pressure has been found to increase theradon concentration in soil air whereas falling pressurecauses a decrease of the radon concentration [Bl 5].
However, a tendency for decreasing concentration withincreasing atmospheric pressure has also been observed
for radon in soil air. This decrease is believed to be dueto a flow of air from outside into the soil surface layers
forcing the soil gas initially in surface layer lo greater
depths. The results of some recent studies are shown in
Tables 8 and 9 [19], which show the inlluence of depth.
barometric pressure and wind speed on the concentration of radon and thoron in soil air. The standard
deviation of the observations are 50% for radon and
25% for thoron. The effect of wind speed is believed tobe due to increased turbulence at the ground surface
which causes a pumping effect on the soil gases.
60. Factors inlluencing the concentration in soil air
also inlluence the exhalation rate, but in the opposite
direction. Rain. snow. freezing and increased atmospheric pressure reduce the exhalation rate, while
higher wind speeds and temperature increase it. Consequently, the radon concentration in soil has its
maximum values in winter, when the ground is frozen,
and in rainy periods, unless the rain llushes out theradon from the soil. Radon exhalation rates vary for
different soils. In areas with a high radium burden, suchas uranium mining areas, the exhalation rate is muchhigher than normal (more than two orders ofmagnitude greater for uncovered tailings) [U9]. Diurnal
variations of exhalation rate have been reported forradon [M2], while others have found the exhalation rate
to be relatively constant between day and night [W15,
Gl 1]. Studies of correlations between radon exhalation
rate and temperature (at 1 m above ground) have given
equivocal results.

direction and strength of the wind and on air turbulence. The radon and thoron daughters are also affectedby precipitation. The temperature in the tropospherenormally decreases with height up to about 11 km,
above which the stratosphere begins. There the temperature is rather constant up to about 32 km, where it
begins to rise again. Most of the air mass, water vapour
and dust are found in the troposphere (75%), and fornormal turbulence conditions most (> 99%) of theradon and its daughter products are found in the
troposphere.
64. The vertical dispersion of radon and thoron takes
place through turbulent diffusion and convection and islimited by the radioactive decay. The turbulent
diffusion coefficient is much higher than the gas kinetic
diffusion coefficient and increases with the height
above ground. This increase with altitude is influenced
by vertical variations in wind velocity and atmosphericstability·in the upper part of the troposphere and in thelower part of the stratosphere, where the turbulent
diffusion coefficient decreases again (13]. Characteristic
profiles of the turbulent diffusion coefficient corresponding to some typical conditions of turbulence areshown in Figure X (adapted from (13)).
10•,---,--,----,--,.--,--,.--,--,~NE.

DISPERSION OF RADON AND THORONIN AIR

63. The transport and dispersion of radon and thoron
in air depend on the vertical temperature gradient, the

E

u

10'

>- ...
,q

61. The exhalation of thoron from soil is more
dependent on soil conditions and meteorologicalfactors than is the case for radon. Because of the shorthalf-life of thoron, the effective exhalation depth is only
a few centimetres and the thoron exhalation decreases
rapidly when moisture content increases. Diurnal variations in thoron exhalation (± 30% of the mean) occur
in dry summer days because of convection streams withmaxima at sunset and at night and minima at sunrise
and early in the day [04, G16, Ml. MlO, S40].
62. Radon exhalation from sea water is about twoorders of magnitude less than from soil. The radium
concentration in sea water is about 1 Bq m-3 and varies
with the depth, being higher (up to one order ofmagnitude) near the ocean floor than at the surface[S26). The radon concentration, however, is not in
equilibrium with radium in the sea water, but it ishigher near the bottom owing to radon exhalation fromthe sea floor and to radium-enriched plankton in thewater. This excess of radon decreases with increasing
distance from the sea floor: in surface water there isactually a relative radon deficiency due to radon exhalation into the air. Measured values of radon concentration are about 1 Bq m-3 or less [H7, S26]. Using a
diffusion coefficient of 10-s cm2 s-1 for radon in water
leads to a predicted exhalation rate of about 10-9 Bq
cm-2 s-I. However, owing to water turbulence, theeffective diffusion depth is much higher than thatderived from molecular kinetic diffusion and the radon
exhalation is at least an order of magnitude higher than
the above value. This higher value is also in better
agreement with the ratio between the radon concentration in air above oceans and land, which is around
10-2.

10'

"'

....

!:;; "''..........
~

1()1

0

u

8

......
0V,::,,o•~~~~~--~--~10-1,o-i 10-•
10

10'

101

10-

11)1

ALTITUOE (m)Figure X. Values of diffusion coefficientused In calculation of vertical concentration profiles of radon-222 end Its
daughters. NNN = normal turbulence
conditions; WNN = weak turbulence
conditions; SSN = strong turbulence[G19]

65. The vertical distribution of radon and thoron andtheir daughters in air can be calculated from thefollowing system of differential equationsd (dz

D.T (z)

dXa 1
'
dz

(z))

-

"-1 Xa 1 (z)

'

=0

(17)

~ (D.T (z) dXa.j (z)) + A.j - 1Xa,j - 1(z) dz

dz- (); + A)Xa,j(Z) = 0

G > 1)(18)

where l:l T(z) is the turbulent diffusion coefficient at theheight z; Xa.1(z) is the concentration of radon or thoron
atoms in air at the height z: Xa,j(Z) is the concentrationof daughter j U > 1) in air at the height z; "-I is the
decay constant of radon or thoron; Aj is the decay
constant of radon or thoron daughter U > 1); and /\ isthe removal rate of daughters caused by washout andrainout and is assumed to be independent of altitude[J3]. Boundary conditions to equations (17) and (18)areXa,j(O) = Oforj > l;andXa,j(cx,) = Oa,jforj ~ 1,
2, 3 ...
151

66. By assuming a constant radon and thoron exhalation rate from an inlinite plane (ground surface) whichequals the radioactive decay of the total radon andthoron content in the atmosphere, it is possible to solve
equations (17) and (18), which, in combination withdifferent values of 6 T(z), give the vertical distributionof radon and thoron and their daughters for different
atmospheric stabilities. The result of such calculations
is shown in Figure XI. It is seen that the radon and
1'

100

I

~-

I

w

•-IJ----i

•-t-t

I
I

I

6.xo I

3·

I

I

----

\

I

\
\

I

'\

10

I

I

...

0
:::,

-----,-~,

,_

\

\

Nt-lN 'a\ ' , , ,SSN::: --........

'

...u

0.1

10

RADON ACTIVITY COflCENTRATION

""z

0.01

z

0
0

ID"'

10'

1~·

10'

ALTITUDE (km)Figure Xl. Vertical profiles of radon and thoron,
assuming an emanation rate of 1 radon atom cm· 2 s·•corresponding to about 210- 2 Bq m· 2 s·' end 0.1
thoron atom cm· 2 s·• corresponding to about
1 Bq m· 2 s·•. JWN =- strong Inversion; SSN - strong
turbulence; NNN .. normal turbulence. The full lines
are for radon and the broken lines for thoron. The
vertical profile of 211Pb Is also shown for normal turbulence conditions (J3]thoron concentrations at ground level are expected tovary by a factor of 100 for the extreme conditions ofatmospheric stability. Assuming a radon exhalation rateof 1 atom cm-2 s-1 (corresponding to 2 10-2 Bq m-2 s-1),
these variations of radon concentration lie between
about 1 and 100 Bq m-J. At higher altitudes these variations gradually reduce to become less than a factor of 5
at 1-2 km. Assuming a thoron exhalation rate of 0.01
atom cm-2 s-1 (which is a fairly normal value) thethoron concentrations at ground level (0.01-1 m) areabout the same or a little higher than those of radon. At
10-100 m height the thoron concentrations are insignificant.
67. Several measurements have generally confirmed
the above theoretical model for the vertical distributionof radon. Radon concentrations at different altitudes
over the Yukon Valley in Alaska were found to lie
within the theoretical curves for the extremes of strong
inversion and normal turbulence conditions, as shownin Figure XII. The radon concentration in air below
2 km corresponds to a radon exhalation rate of 0.33
atom cm-2 s-1 (corresponding to 0.7 10-2 Bq m-2 s-1),
which is remarkably high as the ground was frozen andhad a thick snow cover. This may be explained either
by a high radium content in the soil or by a highdiffusion coefficient for radon from the snow cover[L3]. The radon may also have come from elsewhere.
Radon concentrations at altitudes above 2 km probably
depend on large-scale circulation of air and radontransport from very distant areas, which gives time for
substantial decay.
68. In measurements made by Bradley and Pearson[B8] over Illinois, United States, from 150 m to 5 km
above ground the radon concentration ranged from 2 tol O Bq m-=3 at 150 m and decreased approximately by
152

~

I
I

;:

a:

e

2·

z
w
u

,c

.
•-.~ ')"°'

1000-

0

~%
t:

·-·--... II

I

f-

7!

:

I
I
I

<(

...
8
.

A 16 Frbiuuv 1972
0 17-19 F•bru11y 1972
Febfu11v 1072
' 20
21 hbnury 1972o 22 hbrua;ry 1972

I

5

-'

E

!

6-

100
(Bq m·l/

Figure XII. Radon concentration at different altitudes
over the Yukon Valley In Alaska. The figure represents
the average of 12 measurements over the Gulf andAleaka, The solid curve represents the theoreticalprofile of the exhalation rate of 0.33 atom cm· 2 s·• anda strong Inversion. The broken curve represents theoretical profiles with normal conditions of turbulence(L3]

one-half for every 700 m increase (n- altitude. Thisvertical decrease with height is greater than theoretically expected from the air mixing conditions.
69. Even if some measured radon levels do agree withthe models described above, the models should only
serve as a guide to the understanding of radon levels.
They are not adequate to explain all the variations inradon levels with geographical place, altitude andmeteorological conditions. In practice, the radon exhalation rate varies with geographical location and theland surface is not unlimited, as the theory assumes.
70. Studies of the correlation between radon concentrations in air and meteorological conditions indifferent environments in France have been reported[F8, F9, G20). Measurements of radon concentration at
ground level during several months in combination
with acoustic sounding measurements give a reliable
method for the monitoring of vertical stability above asite [G21]. Radon concentration has also been used as
an atmospheric tracer to follow air mass movements inurban pollution studies [Cl 9).
71. Because of the short half-life of thoron. there aresubstantial difficulties in measuring this gas in thepresence of radon in air. Therefore, actual data on
thoron distribution with height over a few hundred
metres to compare with the models are not available.
Measurements on 212Pb in air are sometimes incorrectly
reported as thoron concentrations. As shown in Figure
XI, equilibrium does not occur at ground level undernormal turbulence conditions (NNN). Only in case ofstrong inversions (not shown in the figure) does
equilibrium occur at ground level (I m above ground)[BJ. There are however some measurements [D4, 15) of
thoron (Figures XIII, XIVa) showing the verticalprolile up to a few metres. Figure XIVb shows thecorresponding prolile for radon. The lower values
observed during the day are caused by greater turbulence in daytime than at night [JS]. The results illustrated in these ligures may depend on local factors andin general are not applicable to all sites and under all
conditions.

7

e
a

"'
~
,_
:i!

'e

160•

a

a,

,oo

,-

...5
<

5
u

I-

:,-

"'
~

~

0

u

100

~

~
w
u

10

ts
~

0

u

...;::;

~
u
>,_

"'

;::;

....U
<

0.1

0.1

10

HEIGHT (m)HEIGHT (mJ

THORON VERTICAL PROF !LERADON VERTICAL PROFILE

(a,)

(b)

HEIGHT (m)Figure XIII. Vertical profile ofthoron In the atmosphere for windspeeds of 4 to 12 m s- 1 [D4]Figure XIV. Vertical profile of thoron (a) and radon (b) concentration near ground level [15]72. A great discontinuity in the transfer of radon to
air occurs at the boundaries of large land surfaces, e.g.,a continent. Owing to the small radon emanation fromsea water it is to be expected that the radon concentration in surface air near the coast should be muchsmaller when the wind blows from the sea than when it
blows from the land. This effect is evident during sea
breeze conditions in the day time when low radonlevels occur, while off-shore wind conditions during thenight usually bring higher radon levels [MIS, S12].
73. Under conditions of constant wind velocity fromthe sea the growth of radon concentration near groundlevel at increasing distances from the coast is determined by the exhalation rate, local turbulent mixing
and the radioactive decay but in practice it cannot be
predicted by current models. Even at distances ofseveral kilometres from the coast variations caused bywind direction occur, indicating a degree of nonequilibrium m the growth of radon concentration[MIS}.
74. With constant offshore wind velocity the radon
and thoron concentration in air above the sea stilldecreases at increasing distances from the coast. Thisdecrease is mainly caused by radioactive decay.
Because of its short half-life the concentration ofthoron decreases rapidly to insignificant values over thesea. On the other hand, continental air can still beidentified several thousands of kilometres from thecoast by its radon content [Pl 1].
75. The concentration of radon in air over the ocean
at large distances from land depends on the direction of
the prevailing wind. A low radon concentration in"marine'' air (some tens of mBq m-3), may rapidly
increase by an order of magnitude or more in case of achange to "continental" air. Such "radonic storms"
have been observed repeatedly [W8, Ll]. Radon has
therefore been used successfully as an indicator of thecontinental contribution to over-ocean air in studies on
air pollution [LS, L4, W9, Wl OJ, and air transportmechanisms [W12J.
76. Radon measurements during shipboard cruises
show very low radon concentrations in maritime air(from less than a few mBq m-3 to about 0.1 Bq m-3) far
from land. In smaller seas like the Mediterranean theradon concentration in air may be of the order of l Bq
m-3, indicating that this air contains much more continental radon than that over the open oceans [Ll OJ. Alongthe coasts of large continents at 1~100 km distance, theradon concentration may still be of the order of 1 Bq
m-3. The variations of the radon concentrations in air
have also been demonstrated in the Arabian Sea andthe Bay of Bengal [R 10, E3]. The level of radon concentrations depended not only on the distance from land
but also on changes in monsoon activity, causing
varying degrees of interaction of continental andmaritime air. Levels of 212pb are generally very low (lessthan 0.1 mBq m-3) [RlOJ.
The radon concentration over an island depends
on the radon exhalation rate from the ground and on
the meteorological conditions. With no wind the radonlevels are caused only by radon exhalation from theisland itself. In windy weather the radon levels may be
increasing inland, in the wind direction, and partly
consist of radon from the island itself and partly ofradon from a distant continent. This has been observedin measurements on Hawaii, where about 25% of radonon the lower slopes of the island was attributable todistant continental sources [M15].

77.

78. The time-variation of radon and thoron concentration in the surface layer of the atmosphere depends
on the variation of the radon and thoron exhalation
rates and the vertical and horizontal dispersal of radon
and thoron. Maximum exhalation is usually observed
during the summer and minimum in the winter.
However, vertical turbulent mixing is also higher inspring and summer, resulting in a decrease of the radon
and thoron concentration at the surface. In autumn andwinter this vertical exchange is smaller and inversions
are frequent. The effect of decreased mixing may
greatly outweigh the decreased exhalation rate,
resulting in increased radon and thoron concentrationsin autumn and winter, and the overall effect may be aseasonal variation with a minimum radon and thoron
concentration in the spring and summer and amaximum in the autumn and winter. This has been
observed by several investigators [Ml, B6, R4, MS].
However, recent studies performed at Chester, New
Jersey, United States, of the variation of radon concentration in air show a seasonal maximum in summer anda minimum in winter. This seasonal variation has been
consistent throughout three years. Since the variations
153

concentration in air (at 1 m) no obvious explanation
has yet been found for these seasonal variations [FSJ.
Figure XV shows the results, including studies on theare out of phase with the normal pattern of the distribution of inversion strength and there is a poor correlation between the radon exhalation rate and radon

.

16

M

E

0-

e

14

z

....<~

12

~

z
..,

~

10

~

0

u

,..

,-

8

;:

....

u

6

<(

~

.:
0
0

<(

"'

4

2-

00 OJ 06 09 12 15 18 21
>

.a;

~

'l'

1.
~ .E
g. g
0

< "'

f .8~
j

E

0

t

I 1
;

ii :; <-~ :;i:' -'iCu.

SEASONAL VARIATIONSDIURNAL VARIATIONS

Figure XV. Variations In radon concentration. The diurnal variations show theannual means for the eight three-hour periods. The seasonal variations show
the overall means for the thirteen four-week periods. The top lines In eachcolumn show the variations of the average for each observation period(19nna, 1978fl9, end 1979/80) [F5]diurnal variations. The hourly data and three-hour
averages were found to be log-normally distributed.
The arithmetic mean and the median values (withinparentheses) were 8.1 (6.3) Bq m-3 for 1977-1978, 8.5(6.7) Bq m-3 for 1978-1979, and 7.0 (6.1) Bq m-3 for

1979-1980. Few thoron measurements exist to demonstrate its variations, but measurements of 2t2Pb may
indicate a similar behaviour by thoron. Examples of thevariations of 212Pb concentrations in air are presented
in Figure XVI [B6].

CHICAGO I L L / ~ ; /

u

10-•

Jan.

Ftb. M.nr. Apr, May June July AL.g. Stp. Oct. No.. Dec.
MONTH 1950

Jeri. Feb, Mar. Apr, May Junl!

July Awg. Sep. Oct. Nov, Dec,

MONTH 1950

Figure XVI. Variations of the 212 Pb activity concentration In air, 1950 [B6]154

79. Other extensive measurements in the United Statesof radon and thoron daughters were made over a
period of 4 years in Cincinnati, Ohio in the early 1960s[G 12]. Daily and seasonal variations were studied.
Minimum radon daughter concentrations occurred in
March and maximum values between August-October.
The maximum levels were not so extended in time as
they were at Chester, but the general shape is in fairly
good agreement.

ground level have also been measured [F21] and show amaximum in March-April and a m1111mum in
December-February. The variations were within afactor of ten and the concentrations of thoron lay in therange 2-20 Bq m-3 for thoron and 0.1-1 Bq m-3 forthoron daughters. Measurements of seasonal anddiurnal variations of radon, radon daughters and 212Pb
have also been reported from Spain [022. G23].
Maxima were observed in the winter and minima in thesummer and the concentrations were 2-3 times lower in
the afternoon than in the morning.

80. Several measurements of diurnal and seasonalvariations of radon concentration in air in France havebeen reported [F20, 013]. The diurnal variations show aminimum at noon and a maximum at midnight and adecrease with increasing altitude (0-100 m) (D 13].
Seasonal variations of thoron and thoron daughters at

81. Another example of strong seasonal variations
was found by Rangarajan et al. [R4]; it is illustrated in
Figure XVII. Since these measurements were made on- - 2 uPb tmoming)- - • - -· 21 4 Pb f•hernoonl• - - x J 7 2pb lmor;;ing)o - - - ~ 212 Pb (af1emoonl

1010o----o 210 Pb

.

E

"

!!!
.D

!:

"i

.

.D

N
N

0.1

0.1

1066

1967

1968

,959

1970

1971

1972

Figure XVII. 2 ,.Pb, 212 Pb and 210 Pb activity concentrations In surface air
In Bombay (monthly mean concentrations) [R4]214Pb and 212Pb, the variations do not quite representradon and thoron variations; nevertheless, they are ofinterest because they are a consequence of several
contributing factors. The minimum in the spring andsummer is caused by increased turbulent mixing, apredominant south-west wind over the Indian Ocean,higher mean wind speeds and intensive rainfall which
affects both the 214Pb concentration in air and theexhalation rates. Seasonal vanat1ons are lesspronounced in areas with cold winters and an earlysnow cover, which greatly reduces the exhalation of thetwo gases. This has been demonstrated by the results ofmeasurements made in Finland [MS] and at a highaltitude station in India [R4]. Diurnal variations aremainly caused by variations in turbulent mixing.
82. Radon and thoron concentrations reach theirmaximum in the early morning and their minimum atnoon or in the afternoon [R4, FS] and the variation is
generally less than one order of magnitude. The resultsof repeated measurements are shown in Figure XV [FSJ.
Diurnal variations of radon concentration do not occur
over the oceans [E3].
83. Dispersion of radon released from point sources
such as geothermal power plants. mine ventilation
outlets, etc., or from sources with a small area extension
follows the normal dispersion kinetics of gases. If thesource may be considered approximately as a point

source, the concentration in the environment may be
estimated by using the ordinary dispersion formula foratmospheric diffusion.
84. The average concentrations per unit release rate
(also called "dispersion coefficients") at various
distances from a "point" source have been calculated
for normal conditions in the United Kingdom as mean
concentrations weighted for the frequency of different
meteorological conditions [812, C20]. The results(based on [C20], fig. 36) are shown in Figure XVIII,
curves 1a, 1b and 1c. The release point is assumed to be
0, 30 and 100 m, respectively, above ground and thedeposition velocity to be zero. Radon releases fromextended sources such as tailings can be considered as anumber of small point sources distributed over the areaof interest. The dispersion of radon from such sources
has been calculated for two area sources, one 1 x 1 km2(106 m2) and another 100 x 100 m2 (104 m2). The surface
was divided into 250 and 100 equal elements, respectively. and the resultant dispersion coefficient at
different distances from the outer frontier of thesurfaces was calculated using curve 1a in Figure XVIII
for each surface element. The values of the horizontal
dispersion parameter cry have been calculated assuminga Pasquill D weather category and the formula ay =0.1471 x0.9031, where x, in metres, is the distance fromthe source. The results are presented in Figure XVIII,
curves 3 and 2, respectively.
155

a

en

la Poinl source, ground level
1b Point source, height 30 m
le Point source, heigh1 100 m
2 Areasource, 100 • 100 m, ground lovul
3 Area source, 1 • 1 km, ground level

,o-1

,w
VI
~

...
--'

0:

s....
...
z
u

25
u

,_

....
....u

""
.......
C...l3""....
;:

,o•

,o'

lo'

10'

01ST ANCE (mlFigure XVIII. Integrated activity concentration of radon per unit
release at various distances from point end area sources, calculated for normel conditions In the United Kingdom. The values ere
given as mean concentrations weighted for the frequency ofdifferent meteorologlcel date as given In [C20)85. The average concentrations per unit release ratetaken from Figure XVIII curves la and lb, for point
sources are approximately inversely proportional to the
distance x raised to the power p. If the activity concentration Xa(X) at distance x is expressed relative to theconcentration Xa(x 0 ) at a reference distance x0 , Xa(x) is
given byXa (x) =

X

(

Xo

)-p

Xa (Xo)(19)With p = 1.5 the formula describes satisfactorily thedispersion and relative concentration at distances
beyond 1 km from a point source (curve la, Figure
XVIII) at ground level, with the reference distancex0 = 1 km. For releases from a height of 30 m or more avalue of p = 1.2 approximates more closely thedispersion curves at distances beyond 1 km.

F. DISPERSION OF RADON AND THORONDAUGHTERS
86. The atmospheric diffusion model of Jacobi andAndre has also been applied to radon and thoron
daughters [J3]. In the case of radon, the concentration
at a given point and its vertical distribution are greatly
dependent on the conditions of turbulence in the
troposphere. At 1 m from the ground the relationshipbetween the octivity of radon daughters and radon
depends on the turbulence but above 100 m the model
predicts approximate radioactive equilibrium. This isalso the case for 212Bi relative to 212Pb. Irrespective of
turbulence conditions there is no general equilibrium
between thoron and its daughters. Other similar models
156

by Staley [S20] and Birot et al. [B5] include time variations for diffusion and dispersion by advection.
Shapiro et al. have developed these models with somemodifications of the boundary conditions [S7].
87. Measurements in the lower atmosphere indicate
deviations from secular equilibrium for radon
daughters. Shapiro et al. [S7] have measured the 214Bi/
214Pb ratio at 20 m under various atmospheric conditions. They have found that afternoon samples taken
for a period of several months had 214Bi/214pb activity
ratios from O to 2.2 with a mean value of 0.67 (morning
samples had a mean value of 0.70). The predicted rangeof the 214Bif214Pb activity ratios according to Jacobi
and Andre [J3] is 0.68-0.98 at a height of 20 m.
"Abnormal" ratios greater than 1, which were all
associated with winds greater than 4 m s-1 are outside
the framework of any simple theory since different
mechanisms must be responsible for these abnormal
conditions. Possible explanations could be selective
removal of radon daughters (e.g., by washout) anddifferent responses to advection owing to attachment toaerosols of different size ranges [S8]. Other measured
values of the relative concentrations of radon daughters
range from 0.8 to 1 for heights between 1 and 90 m
(increasing with height) [H15, H16, 011].
88. Changes in the radon daughter concentration
profiles may influence the natural gamma-ray
background. Thus, after heavy rainfall there is a
depletion of radon daughters in air and a consequent
increase of radon daughters on the ground. The
increase in external absorbed dose rate in air ranges
from 0.5 10-2 to 4 10-2 µGy h-1 [B3, F2], to be comparedwith a "normal" background of 5 10-2 µGy h-1 (Annex
B).

89. The occurrence and behaviour or the relatively
short-lived radon daughters (218Po, 214Pb, 214Bi and
21 4Po) in the atmosphere are strongly dependent on thebuild-up from radon and by their short hair-lives.
Except for the circumstance of rainout, the radioactive
decay time of these nuclides is short compared with anyother removal mechanisms.

III.

RADON AND THORON IN INDOOR

SPACE
90. There is in principle no basic difference in theformal treatment of radon and thoron in a room or in
the open air. However, there are other sources andfactors which warrant separate discussion. The indoor
space may be a house, apartment, mine, cave, tunnel or
any other closed space, with or without ventilation. As
for outdoor air, the levels of thoron and thoron
daughters are low in comparison with those of radonand radon daughters. There are also very few datareported in the literature for thoron and its daughtersand for this reason the emphasis of this chapter will beon radon and its daughters.
A.

SOURCES

91. Radon and thoron in indoor space originate fromemanation of the gases by the walls, floor and ceilings
which are constructed of building material. rock or soil,
by release from materials brought into the room, suchas radon-rich water or gas and by radon or thoron in
the inlet air, which may in turn have a normal concentration of the gases or an increased concentration
derived from sources outside the room. The primarysources are in all cases 226Ra or 224Ra.
92. The radium and thorium concentration inbuilding materials vary for different kinds of material,
depending on their origin. Some published data arefound in Table 10. More detailed information forbuilding materials in Nordic countries is given in
Table 11. The values in the tables are mean activity
concentrations. Some materials such as phosphogypsum, aerated concrete with alum shale and uranium
mine tailings, are known to be much more radioactive
than others: some or them are used only in exceptional
circumstances. Materials with low activity concentrations include wood and natural gypsum. The averagevalues of radium and thorium concentrations in theabove tables are of the order of 50 Bq kg-I. In general
the activity distribution of samples of individual
building materials reflects the activity distribution of
constituents of the building materials from different
parts of a country. In an investigation of radium
content of gravel in 23 of 24 provinces in Sweden, thestandard deviation of all 146 samples was 30% and therange was within 0.5 and 2 times the average. The
standard deviation for samples from each province wastypically 20% [HI].
93. The highly radioactive materials are with few
exceptions by-products from other processes. Phosphogypsum is produced in the manufacture of phosphoricacid from sedimentary phosphate ore; red mud bricks
contain a waste product from the production ofalumina from bauxite; blast-furnace slag is a byproduct of iron production; fly-ash is a waste productfrom the combustion of coal; tailings are wastes fromuranium mining and milling. In recent years there has

been increasing interest in using waste products as
substitutes for natural products in building materials.
However, because of the relatively high radioactive
contents their use is frequently subject to regulation[W20].
94. Alum shales in Sweden have been used for several
decades in the manufacture of aerated concrete and forsome years they provided about one-third of the market
for building materials in Sweden. Production was
slopped completely in 1979. The lower radium content
in aerated concrete manufactured from alum shale
between 1974 and 1979 results from a reduced content
of alum shale.
95. The soil beneath a house can be a significant
source of radon for individuals (05]. This may be
specially true if there are cracks in the base structure.
The radium concentration in soil and rocks varies
widely in different countries and in different regions ofa. country. Special area~ having enhanced or naturallyhigh radium concentration are some reclaimed lands inth~ . United S!~tes following phosphate rock strip
mmmg [U2], ta1hngs from a radium factory in Australia[A8], uranium mine tailings in Colorado, United States[C16], and areas generally adjacent to uranium mining.
The contribution from radium in the soil to the radon
concentration in a house depends on the emanating
power and the thickness and tightness of the basestructure. In residential buildings in New Jersey and
N~w York, United States, the radon exhalation rate per
umt area from cellar floors has been determined. The
average exhalation rate per unit of radium activity
concentration (Bq m-2 s-1 per Bq Ra g-1 soil) for 16
houses was 0.07 ± 0.06 with a range of 0.007-0.21 [Gl].
The thickness of the concrete floor required by local
building codes is about 10 cm. The wide variations
observed may have been due to differences inemanating power of the underlying soil. There may also
have been a contribution from the concrete floor itself
and from deeper layers of the soil. Bare soil in unpaved
crawl spaces has been identified as a major radonsource in some houses in the United States [Rll]. In
Sweden the soil under the house has recently been
proved to be a more significant source of radon thanbuilding materials, both in cases of very high individual
radon concentrations and for general radon exposureof the public [R15). This is also confirmed by thegeneral observation that the radon concentrations inhigh floors of multi-storey buildings tend to be lower
than in ground floors.
96. Another source of indoor radon is radon-richwater. The release of radon from water to air depends
on the circumstances in which it is used and theresulting radon concentration in air is determined by
the ventilation rate. The radon release during typicalhousehold activities has been studied [P2] and for ahouse with volume 340 m3 and ventilation rate of 1 h-1
the average air-to-water concentration ratio has been
estimated to be 0.4 1Q-4. The amount of water used eachday was assumed to be about 500 l per person. The airto-water concentration ratio in dwellings in Finland has
been measured to be about lo-4 [C3]. In other studies
the ratio has been calculated to be 1.5 lQ-4 if fulldesorption of radon in water is assumed [N2] and 1o-4
by another research team [D14]. In Annex B of the
UNSCEAR 1977 report [U6] the ratio was calculated tobe 2 lo-4. The ratio has also been expressed as aformula [GS]
LFa,Rn.k Vw.k

Xa. Rn = ....:l:....__ _ _ __24 A.v V
Xw, Rn(20)

157

where Xa,Rn and Xw,Rn are the radon concentrations in
air and water, respectively; Yw,k is the volume of waterused daily for various applications k; Fa,Rn,k is thefraction of radon released to air for each application k;
Avis the ventilation rate of the dwelling h-1; and Vis thevolume of the dwelling. If ~ Fa,Rn,k Vw,k = 1 m3/d,11.., = 1 h-t and V = 200 m3, the ratio is about 2 J{}-4,
Using this ratio and taking typical values of the radon
concentration in air (10-100 Bq m-3), it is apparent thatradon in water is a significant source for radon inhouses only when the radon concentration in water isof the order of 10 kBq m-3 or more.
97. Natural gas containing radon may also be asource of significance. The industrial processing of raw
natural gas involves the removal of impurities andseparation of hydrocarbons. Some of these hydrocarbons (mainly propane) are bottled under pressure
for sale as liquefied petroleum gas (LPG), while theothers are used for fuel or as chemical feed stocks.
When either gas is burned in houses, radon is released
and enhances the radon level indoors [G6]. The contribution from this source depends on the amount of gas
used, the original radon concentration and the elapsed
time between production and consumption.
98. Radon enters the natural gas in the earth bydiffusion from radium deposits. Uranium minerals areoften associated with carbonaceous deposits and radonin natural gas is therefore not unexpected. Radon
diffuses through the rock along with the natural gas tocollection wells, from which the gas (and radon) is
transported to the gas processing plant. The radon
concentration in raw natural gas at production wells
varies from undetectable values up to levels of the orderof 50 kBq m-3 [U6, H8] (see Table 12).
99. The processing of raw natural gas results in thetransfer of 30-75% of the radon from the natural gas
into the LPG. The remaining radon may be further
diluted if the gas becomes mixed in transit with gas
from other wells with low radon concentration. Duringtransport through long transmission lines and storage
in reservoirs the radon concentration in natural gas in
the distribution system is reported to lie within therange of about 0.04-2 kBq m-3 [W17, J8]. The averagevalue for the United States is estimated to be 0.7 kBq
m-3, except for four States which have an average ofabout 2 kBq m-3 [81].
100. The gas is used for kitchen appliances anddomestic heating. Taking representative consumption
levels of 0.8 m3 d-1 and 2.8 m3 d-1, respectively, and amean radon concentration of 0.7 kBq m-3, the mean
activity introduced in homes is 2500 Bq d-1 (with arange of 130-6500 Bq d-1 [JS]) if the appliances areunvented. If the combustion products are vented
outside the house, this radon source is negligible.
101. The radon concentration in LPG depends on theradon concentration at the well, the transit time fromthe well to the processing plant, the composition of theinlet gas and the type of processing. The overall effect is
an increase in the concentration of radon in the end
product LPG and an enrichment factor of 10 ± 5 withrespect to raw natural gas has been reported [G6].
102. However, the radon concentration in LPG
delivered to the consumer depends, in addition, on thetime delay in a complex network of supply, transit,
storage and delivery facilities which vary in different
countries and different parts of a country. Because of158

decay of radon the concentration may be lower inremote districts than in districts close to the processing
areas. Seasonal variations may also occur owing todifferent storage times, with a minimum radon concentration in the winter when gas consumption is high.
Seasonal variations in concentration of about a factorof 2 have been found [G6].
103. During storage of LPG in domestic tanks theradon concentration is further reduced by decay. Withmonthly deliveries the average concentration of radonat the point of gas consumption is about 20% of theconcentration al delivery.
104. The magnitude of this radon source in homes is
estimated by combining the radon concentration in
LPG delivered to homes, the quantity of LPG used andthe decay factor due to storage in domestic tanks. In
one iqvestigation in the United States the values ofthese quantities have been found to be the following[G6]: radon concentration = 0.4-5.6 kBq m-3; quantityof LPG = 0.3 mJ d-1 for cooking ranges and 1.1 m3 d-1
for space heaters; decay factor = 0.18. For normal
consumption of LPG, the range of radon activity introduced into homes is then approximately 100-1500 Bq
d-1 with a customer-weighted average of about 200 Bq
d-1. The use of LPG is however small compared withnatural gas and, on a national basis, natural gas is a10-100 times greater radon source than LPG.
105. The relative significance of different radonsources for a reference house, defined as having a
volume of 200 mJ and an inner surface area of 350 m2,
are presented in Table 13 (the values refer to data inthis report). For thoron and thoron daughters, the only
significant sources are building materials and theoutside air. The thoron exhalation from building
materials may be up to two orders of magnitude higher
than that of radon, but in practice wall paper and othersealants may reduce the thoron exhalation considerably.
106. In mines, tunnels, caves and other undergroundbuildings the radon sources are rocks, soil and water.
Faces of uranium ore in mines are apparently potential
radon sources, although there are great variations inemanating power. Crushed rock in abandoned parts ofa mine is also a significant radon source in nonuranium mines [Sl2]. Radon in water may often be asignificant source. Drainage or use of large amounts ofradon-rich ground water may cause radon release either
locally or to the ventilation inlet air. This may be thecase in mines, tunnels, caves, spas and undergroundhydroelectric power stations [S13]. With poor ventilation local radon and radon daughter concentration in
air may become very high if the radon concentration inwater is 0.1-1 MBq m-3 or more [S12].
B.

RADON AND THORON DIFFUSION AND
EXHALATION

107. The diffusion through and exhalation of radon
and thoron from building materials, rock walls, etc.,
follow the principles described in paragraphs 56-62.
The emanating power Fr varies for different materials.
Normally the value of Fr varies between 1% and 10%
although extreme values of 0.1% and 30% have beenreported [P4, W4].
108. The diffusion coefficient in a concrete building
material depends on the type of aggregates used in theconcrete. the water/cement ratio used in the mix andthe curing conditions. The diffusion coefficient can be
expressed as t::. 1t or as t;;. .rr = Fhuild,ps, t:. k, where Fhuild,psis the porosity. t:. k is called the effective diffusion
coefficient and t::. cff the effective bulk diffusion coefficient. The presentation of diffusion coefficients in theliterature is not always very clear on this point andmisunderstandings arise easily. This problem is
discussed by Culot et al. [C12]. Another name used in
the literature for effective bulk diffusion coefficient istrue diffusion coefficient.
109. Another source of error arises from the experimental conditions under which the diffusion coefficientis measured. By placing the material of interest in aclosed vessel and measuring the equilibrium radon
activity in the air, the estimated diffusion coefficient islower than that corresponding to emanation into open
air [J9]. This is due to the fact that the difference inpartial pressure of radon in the pores of the material
and in the air space of the vessel decreases with time
and this influences the rate of diffusion.
110. The exhalation of radon and thoron from walls isdependent on the 226Ra and 224Ra concentration in thewalls, the emanating power and the diffusion coefficient. The diffusion coefficient for building material
varies by several orders of magnitude for different
materials and values between 1()--4 and 10-7 cm2 s-t havebeen reported [C12. 19, P8]. Changes of air pressure
have been shown experimentally to influence the radon
exhalation rate from concrete walls [M8]. On reducing
the atmospheric pressure, the exhalation rate was foundto increase linearly with the pressure drop, as seen in
Figure XIX. This effect has also been found in uranium

'=1
2500

. 20001~

waste products. Although promising results have beenachieved, there is not yet full acceptance of the methods
proposed, partly for economic reasons and partly for
uncertainties regarding the overall positive effect. A
sealant may in itself cause harm by being toxic orelectrostatic, etc. A possible negative effect is theincrease in gamma radiation from the daughterstrapped behind the sealant. This depends on thematerial and its thickness and may be as high as 10%.
Data have been published on the qualities of someradon barriers [C14, H3) and on the experience gainedin practical attempts to reduce radon and radon
daughter concentrations indoors [C15]. By plastering
the wall the radon exhalation may even increase if theradium concentration in the plaster is higher than thatin the wall [W4]. By covering the walls with plastic
materials such as polyamide, polyvinylchloride.
polyethylene and epoxy paint (the thicknesses of which
are of the order of 0.1 mm) or by painting three times
with oil-hased paints, the radon exhalation is reduced
by one order of magnitude [E4, P13]. The effect of wall
paper is always to decrease radon exhalation (e.g., 30%
as given by [031), even if it is sometimes marginal. The
reduction is probably higher for thoron, because of its
short half-life.
113. The emanation of thoron from walls depends on
224Ra concentration in the wall, the emanating power
and the diffusion coefficients. Owing to the shorthalf-life of thoron, the emanation may be considered as
taking place only from the outer surface layers. There
are very few measurements of the exhalation rate ofthoron, because thoron daughters in houses are
believed to be less important than radon daughters as apotential health hazard. There are also experimental
difficulties in making such measurements. Experimental data have been reported [M9] on thoron exhalation rates from building materials, relative to exhal.
Bq of thoron
at1on rates of radon. Values of 0.1-0.4 ( B f d )q o ra on
were observed.

7
E

i

1500

a:

1 OOO

C.

~

sOO

RADON AND THORON DISPERSION IN
INDOOR SPACE

1.

0
15

10

20

25

.o.P Imm Hg)

Figure XIX. Variation of the exhalation rate R as a function of
the reduction of air pressure t;;.P [MB]Indoor spaces other than tunnels

114. Assuming instantaneous mixing of radon or
thoron in a room, there will be a homogeneous activity
distribution and the concentration in a room can befound by solving the following equation

mines and has been explained as the result of increased
air flush through radon-rich cracks and fissures into themine [P5, P6].

dx.. (t)s Ak_d_t_ =RV+ V + Xa,inAv-Xa(t)(A.+Av) (21)111. The exhalation rate of radon from building
materials has been studied extensively. However. thevalues obtained are not always consistent and large
variations are found for the same material and surface.
There are obviously great experimental difficulties andfactors influencing the measurement are not fully
understood. Reported values of the radon exhalation
rate per unit concentration of 226Ra in building
materials normally lie in the range of lQ-6 to 1()--4 Bq
m-2 s-1/(Bq kg-I) with several values in the higher partof the range [Gl, P8, J9, S25, M17. W4).

where Xa(t) is the radon or thoron activity concentrationin the room at the time t; R is the radon or thoron
activity exhalation rate per unit area; S is theemanating surface area: V is the volume of the room;
Ak is the activity release rate of any other source in theroom (water, gas); Xa,in is the radon or thoron activity
concentration in the inlet air: A.vis the ventilation rate(h-1); and "' is the decay constant of radon or thoron.

112. Radon emanation can be reduced by applying asealant to the emanating surface. This is of particularinterest for houses built on uranium tailings or other115. At equilibrium the concentration in the room isgiven bys Ak.
RV+ V + Xa,inA.v
Xa =>..+ >...,

(22)
159

Jn homes 0.1 < )..y < 3 h-1. Since for radon). - 7.6 J0-3
h-1, Av >> ). and expression (22) takes the form

Wind dlrKtion,oo•

111"-G(J-rt
l
-so·

s Ak
R-+V

Xa.Rn -A.yV

+ Xa, Rn,in(23)

As long as Av >> A and Xa,Rn,in is negligible, the radon
concentration indoors is inversely proportional to theventilation rate. As the ventilation rate increases from 0
to 0.1 and from 0.1 to 1 h-1, the radon concentration
decreases by a factor of 13 and 10, respectively. For
thoron ).. = 45 h-1 so that A >> )..y and expression (22)takes the form (Ak is assumed to be negligible)

..,
'E
CT
a,

1600

z

0

s
.....

R~+"'·T.
1V
A.a, n, an "'Y
Xa, Tn = ----).----~uzu>- 1 OOO

0

(24)

!::

'

::....
u""This means that the thoron concentration in room air isalmost independent of the ventilation rate, as long as
the contribution from outdoor air is small. The concentration of 212Pb, on the contrary, is inversely proportional to the ventilation rate, down to about 0.5 h-1 andthereafter it approaches the activity concentration ofthoron.

SOO

116. The numerical value of Xa.Rn for radon in areference house such as that described in paragraph 105
is
Xa. Rn =

:. :
I

Wind
dirfC'tion

0

0

0

.

0

.

-.C50

-90

0+--.----l-,---,---,--1----,---,-~+--.---.24

12

12

24

12

24

12

TIME OF THE DAY (h)( 2 10-3 Bq m- 2 s- 1 3600 s h- 1 1.75 m- 1 +Figura XX. The dependence of the radon concentration Ina detached house with a natural draught ventilation
system on the wind direction. The door to the room wasclosed at the beginning of the measurement. (Measurements taken In winter) (S30]

4 ID3 Bq d- 1 + 3 103 Bq d-1)+
/05h- 1 +•24hd- 1 200m3+ 4 Bq m-3 = 12.6 + 1.45 + 4 = 32 B -3
0.5
qm
The relative importance of radon sources may bedifferent in different parts of a house and in case of
inhomogeneous mixing of air in the building the radon
concentration will vary within the house. In the cellar
the radon exhalation rate is often higher than in theupper floors. The ventilation rate is also often less andthe radon concentration is therefore normally higher inthe cellar than in the upper floors. Water as a radonsource is of significance in the kitchen, bathroom andlaundry. It contributes specifically to radon daughter
exposure because it becomes available as a source whenpeople are using it.

Bqm-3

5

;:
<
a:

500

...z

~

z

10

Window

0

u

250

z

8
<
a:

117. The variations of the radon concentration in abuilding are mainly dependent on the variations of theventilation conditions and air exchange between rooms.
These are caused by meteorological conditions (wind,barometric pressure, temperature) and by human activities such as opening windows and doors. Some of theseeffects are shown in Figures XX and XXI (S30]. There
are also other variations caused by changes of theradon exhalation from surfaces. The variations candepend on pressure change (see paragraph 110) and acorrelation between radon concentration in a room andbarometric pressure has also been observed (JlO).

Figure XXI. Variation of the radon concentration In anapartment house built of elements of both ordinary concrete
and aerated concrete baaed on alum shale and with forced
ventilation system for the exhaust air. (Measurements taken
In winter) [S30]118. Diurnal variations of the activity concentrationsof radon, thoron and their decay products have also
been measured [P14]. These variations follow the same
pattern but the relative change is much smaller forthoron than for radon, as expected from equation (24)and as can be seen in Figure XXII. This figure also
illustrates the effect of changes in ventilation conditions.

160

D

12

...
~ :111111111
...a:

24

:I:

Cl

"'0
z

i

1

12

24

12

24

TIME (h)II I 111111111

m,-1,_ LEE SIDEI--

WIND ALONG THE FACADE~

made in 12 rooms and the concentration data together
with 24 meteorological variables were used for
regression analysis.

50
40

lO

Ji

20

o,
12

14

16

,o

IB

12

1s1

l

.C.

6

8

10

11

TIME OF THE OAV (h)Figure XXII. Dlurnal variation of concentration ofradon, thoron, and their decay products Indoors
and outdoors of a typical dwelling (P14]119. A study of the correlations between concentration of radon, radon daughters and thoron daughtersand meteorological variables has been made in
Innsbruck, Austria [S21]. About 750 measurements were120. Tables 14 and 15 show the results of activity
measurements in the houses, taken from this study[S21]. ~ x is the largest observed increase of the activity
concentration within 24 hours. The mean radon
concentration in the open air of Innsbruck was 13.3 Bq
m-3 with a maximum of 96 Bq m-3. The mean radon
activity concentration in living and working rooms
ranged from 28 Bq m-3 to 115 Bq m-3 with a maximum
value of 276 Bq m-3. The mean thoron activity concentration in all rooms ranged from 3.7 Bq m-3 to 41 Bq
m-3. About the same range of thoron concentrations· were found in the open air near ground level (1.5-1 m).
The observed concentrations of 212Pb were all considerably lower than those of thoron, with mean values
between 0.3 Bq m-3 and 4.7 Bq m-3. The mean activity
concentration ratio 212Pb/220Rn was 0.019 (range 0.0090.49). Table 16 summarizes the results of the regression
analysis for radon and thoron with the statisticallysignificant meteorological variables. Other variables,such as mean cloud cover, daily maximum wind speed,change of temperature gradient between morning andnoon and noon to morning, and all other variables withtime scales greater than 24 h were found not to besignificant.
121. Measurements made in Norway [S24] (Figure
XXIII) also show the variation of radon concentration- - Radon concentraticn- - - - - Atmospheric pr11,surt

2.5
,
M

_,,,.

-------,,-....

740

'

'e

g

=

ROOM A

''

730

1.5

....
"'e::

720

i

5

!=!

w

0
u

>-

....

a:

:::,

DAYS

0.15

~
w

ROOM B

a::
~

:!:

a:

t-

u

"'5

00

:,:

,~,--- .... , ... _-- _,,,,,. ...

0.1

C
<(

"'

'

/

--

760

<

I

750

005
740

DAYS

Figure XXIII. The variation of radon concentration In an unventilated room (A) and In an
artlflclally ventilated room (B). Measurements taken In winter (A) end spring (BJ (S24]in rooms as a function of the atmospheric pressurechanges. Room A had poor ventilation and room B had
artificial ventilation which was different for day andnight. This explains the great diurnal variations.
122. In houses built with a crawl space or withradium-rich waste products as filling material underneath the house, the radon concentration can change
substantially with meteorological conditions [S31]. Thisis believed to depend on the variations in the pressure

difference between the house and the crawl space andon the variation in the ventilation of the crawl space
itself. In a special study of the influence of windstrength and direction [W2] it was found that inordinary houses radon may decrease normally by afactor of 2-5 as the wind strength increases up to 10 m
s-t. This influence is particularly important when thewind flows along the facade of the room of interest. In
houses built with a crawl space the radon decrease may
be as much as a factor of 100.
161

123. Diurnal and seasonal vanattons in houses werestudied over the long-term [S18, 01, S32, D2, HS, JI 1,
M7, S44]. Diurnal variations depend on the climate,occupancy and kind of ventilation (natural or forced
ventilation) all of which affect the air exchange rate. In
measurements in the United Kingdom [01) the radon
concentrations showed maxima during the night. In
Finland [M20] the average values of all measurements
in 37 dwellings showed maxima in the early morningand minima at noon, as shown in Figure XXTV. In

the ventilation rate. However, the radon sources are notalways easily identified and the ventilation rate mayvary unpredictably due to human activities. Under
controlled conditions it is possible to obtain good
agreement between calculated and observed values[06). In 16 residential buildings in New Jersey and New
York measurements were made. predominantly incellars, of exhalation rate, ventilation rate and radon
concentration [B10]. By taking the relevant factors into
account, the correlation found between the calculated
and measured radon concentrations was very good(correlation coefficient 0.94), as shown in Figure XXV[B10]. Figure XXVI shows the estimated variation of

M

'e 76
WINTER

<T

"'

=

...8
...:

.......z so

'e

c.:

<T
a,

I,,!

0

z

u
>-

0

~

!::

...
>

~ 150
u

25

5
0

a"'u

"'

§: 100

u

<C

~

<C

t-

...

12

16

20

~

24

z

0

~ 50

TIME OF THE DAY (h)...
0

Figure XXIV. Diurnal variation of radon concentration In winter and summer [M20]

Ld

'"'

-'
:::,
u

-'

measurements made in the United States [S44] themaximum values were found in the morning andminimum at night. These diurnal variations occurredbecause of the use of cooling units during the nights[S44]. Variations by a factor of 10 or more between theminimum and maximum values were reported.
However, the daily average values of the radon concentration during a week normally vary much less, within± 50% of the weekly average. These observations
emphasize the need of continuous measurements or ofseveral samples over at least 24 hours in order to obtaina representative value of the mean radon concentration ,.,in a house. If the radon concentration indoors is of the 'esame order of magnitude as that outdoors, the same
diurnal variations occur indoors as outdoors [H5]. The 0z 100
variations found illustrate the difficulties in obtaining a ...
representative value for radon and thoron daughter F-z
exposure. Some of the uncertainty derives from the fact ....~
that only the levels occurring when the house is 0u,_
occupied determine the exposure, while levels at other !::times are irrelevant. This is discussed in [S44].
t;,=:124. There are very few measurements of the seasonalvariation of radon concentration in houses. In New
York City during a period of two years (1972-1973), theseasonal variation amounted to a factor of 3 between amaximum in summer and a minimum in winter, i.e., thevariations were within ± 50% of the yearly average[F3]. A few measurements in New Jersey comparing theradon activity concentrations in the basement of ahouse in winter and summer indicate that 30% lower
values occurred during the summer [S44]. In anotherstudy in Austria over six months, a minimum was
obtained in May and a maximum in January. The variations of the monthly means were within ± 30% of theoverall average. The maximum in winter depended on
inversion outdoors [S21].
125. If all relevant factors were known quantitatively,
it would be possible to determine the radon concentration indirectly by measuring the exhalation rate and
162

50

'u"'

100

150

MEASURED RADON CONCENTRATION (Sq m·>i

Figure XXV. Calculated radon activity
concentration versus measured radon
concentration In cellars [B10]
RADON EXHALATION RATE pCim"'h" 1

100

10

1000

_,

S/V = 1.33 m

Xa,P.n,in = 4 Ilg n

-3

I
I

10

I
I

I
I

----- ---

I

I-------T-----------OUTDODR RADON CONCENTRATION

1

:

:

I
I
I

I
I

I

I

I

'
0.1

10

100

RADON EXHALATION RATE Oqm··11·•

Figure XXVI. Radon activity concentration In room air as afunction of the radon emanation rate for different values of theventilation rate. The region marked with vertical broken lines
corresponds to measured emanation rates from concrete [M17]

the radon activity concentration as a function of exhalation rate from building materials for various values ofthe ventilation rate [M 17].

2.

TunnelsD.

126. In principle, equation (23) for radon concentration in air is also applicable to mines and other
underground spaces. However, owing to the great
lengths of the tunnels in a mine. it is inappropriate toassume instantaneous mixing and homogeneous distribution of radon in the whole tunnel. Equation (23) may
therefore be written in the form

Xa, Rn (X) =R p X + Ak
V

+ Xa, Rn, in(25)

where R is the radon exhalation rate per unit area in themine; p is the peripheral length of a section through amine tunnel; x is the distance along the mine tunnel: Ak
is the radon release rate for a source in the tunnel (e.g.,radon-rich water); vis the volumetric air flow rate; andX,a,Rn.in is the radon concentration in the inlet air (which
may have passed other mine areas and which may havebeen contaminated with radon).
127. When Ak and Xa,Rn,in are small, the radon concentration increases continuously along the tunnel.
However, the kind of ventilation system and the natureof the radon sources will greatly influence the level andchanges of level of radon in a mine. Large radon
release rates Ak from uranium faces or radon-rich water
will be rapidly diluted and transported along the tunnel
or in ventilation tubes. Where radon-rich ventilation air
Xa,Rn.in from abandoned parts of a mine is allowed toenter active mining areas. it may give rise to an
additional and rather constant radon concentration
along the tunnels. The increase in potential alphaenergy concentration of the radon daughters increases
with the distance x along the tunnel from the ventilation point, and is proportional to x1.ss [G24].
128. Diurnal and seasonal variations in radon concentration also occur in mines. The diurnal variation isespecially pronounced at the time of the year when thetemperature difference outdoors and in the minechanges sign over 24 hours. The resultant effect is aminimum during the night and a maximum during theday [S14]. The variation has been found to be ± 20% of
the daily average. The seasonal variations may begreater, ± 50% of the yearly average or more. with amaximum during the summer and a minimum during
the winter. as can be seen from Figure XXVII [S14].

M-

6

,-z

uo

Zc(

00:

129. A number of measured values of equilibrium
factor F for radon daughters were given in Annex B of
the 1977 report of UNSCEAR [U6]. No direct measurements on radon and radon daughters in houses with F
values higher than 0.5 had been measured and the value
chosen at that time was 0.5. Some new data have since
been reported. In 21 New Jersey and New York
residences the average fraction of unattached radon
daughters was 0.07 and the F value for cellars was 0.52
± 0.11. for first and second floors 0.63 ± 0.14, and foroutdoor air 0.79 ±0.11 [Gl]. The difference between F
values for cellar and upper floors is not significant, but,
if correct, could be explained by assuming that thecellar is the main radon source for the upper floors as
well, and that the ventilation of the cellar is mainly
determined by ventilation of these floors. The radon
concentration in the cellar was on average 73 ± 44 Bq
m-l and on the upper floors 34 ± 26 Bq m-3.
130. Measurements in apartments in the Federal
Republic of Germany gave an average value of theequilibrium factor of 0.4 ± 0.1. The results were basedon 38 measurements and Figure XXVIII shows the
distribution of the results [W14].
15

J

<

N • 38....,_

F • 0.40 ! 0.10

>
a:

:,:

u..
0

....a:

I
0. J

0.2

0.3 0.4 0.5 0.6 o. 7 0.8 0.9
rouJLIBRIUM FACTOR F

Figure XXVIII. Frequency distribution of equlllbrium
factor F for radon daughters In apartment rooms,
based on 38 measurements [W14]131. In an extensive investigation of the naturalradiation in houses in Austria, radon and radon
daughter activity concentrations were measured in 250
houses in Salzburg. The mean ratio 2t4Pb/222Rn was
found to be 0.62 ± 0.08, corresponding to a value of Fof slightly less than 0.62 [S22].
132. Measurements in single-family houses in Sweden[S33] have given an average value of F in 3 houses of
0.45 ± 0.11 (range 0.28-0.65 in different rooms) with amean radon concentration of 470 Bq m-3. The range ofthe distribution of F values in different rooms was
narrower for each individual house than between
houses and the standard deviation lay in the range
10-25%.

'e<;::

EQUILIBRIUM FACTOR FIN INDOOR AIR

J

01-

"""'w
0:

~
u

2

1971

1972

YEAR

Figure XXVII. Radon activity concentration In the return
air of Persberg Mine meesured once a week [S14]133. Another investigation concerned 12 single-family
houses in Sweden [S34], 7 of which were built on waste
piles from the milling of alum shale processing many
years ago. With the exception of two houses, whichwere excluded because of extraordinary conditions, theaverage value of the equilibrium factor F was 0.60 ±0.18 for the cellar and 0.60 ± 0.14 for the upper floor.
In all houses the ventilation rate was measured bytracegas methods, and in Figure XXIX the values are163

0 Houus on ordinary wilo.e

F value of 0.7 may be used. For many non-uranium
mines the ventilation is good and Fis lower than 0.7. In
poorly ventilated mines however the value of Fis likely
to be higher than those given above.

IV.

a

EXPOSURE-DOSE RELATIONSHIPS
A.

0.7

"

VENTILATION RATE (h" 1)

Figure XXIX. Equlllbrlum factor F In houses with different
ventilation rates [S34]plotted together with theoretical data taken from
Table 5 and, also corrected for plateout, using a factorof 0.6 for Aa = 1000 h-l (see paragraph 34). There is nocorrelation between F and the ventilation rate in Figure
XXIX and the F values are often higher than expectedeven for a rather dusty atmosphere. However, all values
are less than predicted from Table 5, with no correction
for wall deposition. Even if it is difficult to explain thehigh F values on a theoretical basis, there is experimental evidence that F values higher than thosepredicted do occur and are often higher than 0.5.
134. Other measurements, however, indicate lower
values of F. In March Township, Ontario, Canada [L7]an average equilibrium factor of 0.38 was obtained. In
measurements in 25 dwellings in Norway [S24] themean value of F was 0.5 with a range of 0.3-0.8; in 35
dwellings in Finland [M20) the mean value of F was
0.47, with a range of 0.30-0.63 (Table 17), and in the
United Kingdom a mean value of F = 0.5 ± 0.2 wasobserved from measurements in 200 houses [07].
135. The equilibrium factor in mines is highly
dependent on the ventilation rate and the distance fromthe radon source. It can be estimated from publisheddata on radon and radon daughter concentrations. The
results from 60 measurements in uranium mines in New
Mexico and Colorado. United States [R3], corrected by
Kotrappa and Mayya [Kl2], give an F value of 0.29 ±0.16. Another compilation of several measurements inuranium mines in the United States gives an averagevalue of F of 0.32 [H21) and in uranium mines inFrance an average value of F of 0.17 is used [Pl7]. In
non-uranium mines average F values of 0.5-0.6 in
Norway [Ml9, S54], 0.7 ± 0.1 in Sweden [S15], 0.7 in
non-coal mines in the United Kingdom [S52] and 0.3 in
Poland [D15] have been found.
136. In view of the variations in the F values found in
the measurements there is no good reason to change theaverage value of 0.5 adopted in Annex B of the
UNSCEAR 1977 report [U6] for houses, bearing in
mind that this value may lead to an underestimate of
the equilibrium equivalent concentration in poorly
ventilated houses. For uranium mines an F value of 0.3
is probably applicable while for non-uranium mines an
164

INHALATION

137. The inhalation of 220Rn-or 222Rn-gas itself
leads to a rather uniform distribution of these noble
gases in the whole body. Due to the low solubility ofthese inert gases in body tissues the resulting effective
dose equivalent from the inhalation of radon gas itself
is normally small compared with the radiation dosefrom inhaled radon daughters; only in ore bodies witha very low equilibrium factor does the contribution
from .radon have to be taken into account. The
following discussion is therefore concerned mainly withthe estimation of the relationship between the exposure
or potential a-energy intake of short-lived radon
daughters by inhalation and the resulting dose in target
tissues of the Jung.
138. As mentioned in Annex B of the 1977 report[U6), in the special case of inhaled short-lived radon
daughters the dose to the bronchial epithelium isconsiderably higher than the dose to the pulmonary
tissue or the mean dose to the total lung. The cells at
risk from the a radiation by radon daughters which aredeposited on the surface of the bronchial airways andtransported upwards in the bronchial tree by the
mucociliary escalator are assumed to be located in thebasal cell layer of the bronchial epithelium [I13].
Therefore the lung dosimetry for inhaled radon
daughters has to consider two target tissues in the lung:the tracheobronchial basal cell layer (T-B) and thepulmonary epithelium (P), the latter including thealveolar region and the non-ciliated terminal
bronchioles. In the cases of the longer-lived 222Rn
daughters 210pb and 21opo, and of the 220Rn daughter
212Pb, a considerable fraction of the activity depositedin the respiratory tract is transferred to tissues otherthan the lung. particularly to bone and kidney. The
dose to these other tissues can be evaluated by applying
the dose assessment models for internal exposure
described in Annex A.
139. The analysis of the dose distribution in the respiratory tract from inhaled radon daughters proceeds fromthe calculation of the equilibrium activity distribution,
taking into account the deposition pattern, themucociliary clearance in the bronchial tree, the possible
uptake and retention in epithelial tissues and thetransfer to blood. An important parameter for theevaluation of the dose to the bronchial basal cell layer
is the depth distribution of this cell layer throughout thebronchial tree. The limited knowledge about this depth
distribution has been one of the main sources of uncertainty in previous dosimetric models. Information now
available, particularly the experimental data from
Gastineau et al. [025), offers the possibility of reducing
this uncertainty. In addition, more realistic data about
the fraction of unattached daughter atoms and about
the activity median diameter (AMD) of the aerosol
which carries the daughter atoms are now available, as
outlined in the previous chapters. Together withimproved models of the anatomical structure of thebronchial tree, this information allows a more realistic
estimate of the exposure-dose relationships for thetarget tissues in the lung.

140. On the basis of this knowledge improved
dosimetric models for the inhalation of short-lived
radon daughters have been developed since the publication of the 1977 report [U6]. Of main importance are
the studies of Harley et al. [H24), Hofmann et al. [H12],
Jacobi et al. [J13, 118) and James et al. (J19]. The resultsof these studies have also been used by the ICRP for theassessment of occupational limits for the inhalation of
222Rn, 220Rn and their short-lived daughters on thebasis of a dosimetric approach (113]. A comprehensive
summary and comparison of these dosimetric models
and their results has been prepared by an expert groupof the NEA/OECD (see [J19]). In this report a sensitivity analysis was also performed showing theinfluence of the various physical and biologicalparameters on the dose to the target tissues in the lung.
141. All of these new studies agree that under typicalconditions in mines, as well as in houses, the dose
distribution over the basal cell layer of the bronchial
generations from inhaled radon daughters is not so
inhomogeneous as was previously assumed but shows arather broad maximum in the region from the lobar
bronchi down to the upper bronchioles. Thisconclusion is strengthened by the fact that each study
used different models for the anatomical lung structure,
for the deposition and retention of radon daughters,
and for the depth distribution of the basal cells. Only inthe case of abnormally high values of the unattachedfraction of the total potential alpha energy of thedaughter mixture should a significant peak in the dose
distribution be expected in the segmental bronchi, andthis only if an increased deposition of unattachedatoms due to turbulent air streaming in the upper
bronchi is assumed. On the basis of these findings amean dose to the bronchial basal cell layer can bederived, averaged over the above mentioned bronchial
generations.
142. From the dosimetric models it follows that theconversion factors between the inhaled potential alphaenergy intake Ipo1 of the daughter mixture and thecommitted dose equivalent H to the bronchial basal cell
layer and to the pulmonary epithelium shows a nearlylinear relation with the unattached fraction fp of thetotal potential alpha energy of the daughter mixture(26)

inhaled potential
daughters ofalpha-energy

intakeof

222Rn(HT-B/lpo1h22Rndaughtcrs = 15 - 40 Sv J- 1
where a quality factor Q = 20 is applied for alpharadiation. For areas with relatively high dust concentration a value in the lower part of this range should be
expected, whereas for highly-ventilated areas with low
dust concentration a value in the upper half of thisrange might be more appropriate. For the pulmonary
epithelium, the dose equivalent per unit potentialalpha-energy intake is(Hp/lpo1h22Rn daughters = 2 - 5 Sv J-I
Thus, on average, the dose to the bronchial basal cell
layer is about a factor of 5-8 higher than the dose to thepulmonary region. As mentioned earlier, the variation
with breathing rate of these dose equivalents per unit
intake is relatively small and falls within the quoted
range. For an AMD of 0.1 µm, which might be typicalfor outdoor air, the dose equivalents per unit intake areabout a factor of 1.5 higher than the values given above.

144. In the case of inhaled 222Rn daughters the dose totissues other than the lung is rather small and can beneglected in the evaluation of the effective dose equivalent. For the evaluation of the weighted lung dose
equivalent a weighting factor w = 0.12 is usuallyapplied to the mean lung dose equivalent, when the
total lung is considered as target tissue (see Annex A).
For the special case of inhaled radon daughters this"mean lung dose" concept might not be appropriate,
because of the considerably higher dose to thebronchial epithelium. Following the recommendationsof ICRP [113], it might be reasonable to split theweighting factor for the total lung and to apply aweighting factor w = 0.06 to each of the two target
tissues in the lung. From the values of the dose equivalents per unit intake given in paragraph 143, thefollowing figures for the effective dose equivalent perunit inhaled potential alpha energy of 222Rn daughters
can be derived:
Mean lung dose concept= 0.12)

Her1/lpo( = 0.3 - 0.8 Sv J-1

Regional lung dose concept

H011/lpot = 1 - 3 Sv J-1(W1ungHr/lpo1 = ap (I - fr)(27)

The first term a in these equations gives the conversion
coefficient for the attached daughters, which depends
on the activity median diameter (AMD) of the carrier
aerosol. The influence of breathing rate on the quotientof the dose equivalent to the intake is relatively small. It
is of great practical importance that these linear
relationships are nearly independent of the equilibriumof the daughter nuclides ratios and therefore of thecorresponding equilibrium factor F.
143. The available measurements in mine areas aswell as in houses indicate that the unattached fractionf p of the total potential a-energy of 222Rn daughter
mixtures is relatively small. Averaged over long periodsof time fp is equal to about 0.05 (see paragraph 20).
Under these conditions with an AMD = 0.2 µm, thedifferent dosimetric models give a mean dose equivalent to the bronchial basal cell layer per unit of(WT-8 = Wp = 0.06)

These values refer to an AMD = 0.2 µm and can beapplied for the occupational exposure in mines and forthe indoor exposure in houses. In this report a reference
value of (Hcrrllpo1h22Rn daugh1cn = 2 Sv J-1 is used,taking into account the high dose contribution to thebronchial basal cell layer. It should be noted that the
ICRP recommends an effective dose equivalent perunit inhaled potential alpha-energy intake of ll2Rndaughters of 2.5 Sv J-1 for the radiation protection ofworkers in mines [113). This value was derived on thebasis of a comparison of the dosimetric approach withthe observed excess lung cancer risk of radon-exposedminers, particularly uranium miners. For the exposurein outdoor air a value of 3 Sv J-1 is used for 222Rn
daughters in this report.
145. Dose equivalents per unit intake of inhaled 220Rn
daughters can be derived in a similar way from the new165

dosimetric models [J 13, J 19]. Table 18 shows theresulting dose equivalent in the target tissues of the lungand in other relevant tissues per unit of inhaledpotential alpha energy, separately for 2I2Pb and 212Bi,
which are the most important daughter nuclides of
2~0Rn. The values refer to an AMO of 0.2-0.3 ~1111. The
dose range given is based on a transfer half-life timefrom the lung to blood of 0.2-0.5 days, as it follows
from human inhalation studies with 212Pb [HIS]. The
dose equivalent per unit intake for tissues other thanthe lung were evaluated by applying the dosimetricmodels recommended by ICRP [IlOJ (sec also Annex
A). It follows from Table 18 that, in addition to thedose equivalent to the lung, the dose equivalents tobone surfaces, kidney and liver have to be taken into
account. With respect to the effective dose equivalent
the difference between the two weighting concepts forthe lung is small. The potential alpha energy per unit
activity inhaled is about 10 times higher for 212Pb thanfor 212Bi. This means that if a mixture of both radionuclides is inhaled the contribution to the dose equivalentfrom the inhaled 212Pb is dominating. In this report areference value

is used for the evaluation of the effective dose equivalent per unit inhaled potential alpha energy of 220Rn
daughters. This value is applied to the occupational
exposure in mines as well as to the natural exposure
from these nuclides. The ICRP recommends aneffective dose equivalent per unit inhaled potentialalpha-energy intake of 0.8 Sv J-1 for occupational
exposure to these nuclides [113]. It should be noted thatthe effective dose equivalent per unit of inhaledpotential alpha energy of these 220Rn daughters is about
one-third of the corresponding value for short-lived
222Rn daughters. Compared with 212pb + 2128i thecontribution from inhaled 220Rn to the effective dose
equivalent is normally small. For the inhalation of
220Rn + 216Po an effective dose equivalent per unit
activity of inhaled 220Rn of about 1 10-10 Sv Bq-1 has
been estimated [J13]. where the main contribution
results from the alpha emission of these nuclides in the
air volume of the lung.

[I 13]. Taking into account a working period T = 2000
hours per year, this yields an inhaled air volume of V =2400 m3 during this period. In Table 19 the resulting
conversion coefficients between potential alpha-energy
intake iih or the radon daughter exposure Cpo1, respectively, and the effective dose equivalent are summarized
for occupational conditions in mines.
148. For the evaluation of the population exposure byinhalation of radon daughters in houses an averageoccupancy factor of 0.8 was assumed. This corresponds
to an average residence time ofT; 11 = 19 h d- 1 = 6935 h a- 1
indoors, andT 0 u1 = 5 h d- 1 = 1825 h a- 1
outdoors. In Table 20 the assumed breathing rates
during the indoor and outdoor residence periods are
given. The corresponding average breathing rates are as
follows:

during the indoor residence period, andl;h,out = 1 m 3 h- 1 = 5m 3 d- 1 = 1825m 3 a- 1
during the outdoor residence period. The averagevolumes of air inhaled in a year are thus V; 0 = 5473 m3
and Yout = 1825 m3 during the indoor and outdoor
residence periods, respectively.
149. The annual inhaled potential alpha-energy intakeof radon daughers is(29)

146. The potential alpha-energy intake Ipot by inhalation during a time period T is given by the relationshipfor the indoor residence period, andIpot (T) = V (T) Cro1 = t;h T Cpot = l;h Cpo1

(28)

lpo!, out = (V Cpo1)oul = (i;h T Cpo1)out = (iih Cpo1)ou1
where Cpot is the mean potential alpha energy concentration in air and V the total breathing volume during
the time period T. The inhaled air volume V is the
product of T with the mean breathing rate Lh during
this period. The product Cpot = Cpot T is called thepotential alpha-energy exposure during the period T.
On the basis of this relationship, conversion coefficients
between alpha-energy exposure Cpot and dose equivalent can be derived from the given dose equivalents
per unit intake. The SI unit for the potential alphaenergy exposure is J s m-3 or J h m-3. Older units like
WLM or WL h are defined in paragraphs 12 to 16,
where the conversion coefficients between the potentialalpha-energy concentration and the equivalentequilibrium concentration (EEC) of radon are also
given.
147. For the occupational exposure of miners a mean
breathing rate iih = 20 1 min-I = 1.2 m3 h-1 is assumed
166

(30)
for the outdoor residence period. Cpo1 is the radon
daughter exposure, which is the time integral of theradon daughter concentration during the time period
considered. In Table 21 the reference values for theeffective dose equivalent per unit of inhaled potentialalpha energy and per unit of radon daughter exposure
are summarized. These values are used in this report for
the evaluation of the population dose from radon
daughters indoors and outdoors.
150. For practical purposes it is reasonable to give
direct conversion coefficients between the concentrations indoors and outdoors and the expected annual
effective dose equivalent. The quotients of the annual
effective dose equivalent to the potential alpha-energy
concentrations are given by the relationships

Herr, in . (LJ

-C
. =

r elf

/I

) V

pot inV.
inA.

{'01, 111

(32)

where Herr/Ipo1 are the effective dose equivalents perunit potential alpha-energy intake, given in Table 21:
and V;n and Vou1 are the annual inhaled air volumes
indoors and outdoors, as given in paragraph 148. The
values of Hcrr/Cpo1 are presented in Table 22. Taking
into account the relative volumes of air breathedindoors and outdoors, the annual effective dose equivalent per unit inhaled activity of radon daughters is
estimated to be 1.3 10-8 Sv Bq-I.
151. The reference values for the dosimetric coefficients given in Tables 21 and 22 refer to adult membersof the public. Correction factors should be applied for
infants and children, taking into account the change oflung mass and breathing rate with age. An agedependent Jung model has been developed by
Hofmann et al. [H12] and applied to the inhalation ofradon daughters. This model indicates that for a given
radon daughter concentration in air the effective dose
equivalent probably reaches a maximum value at theage of about six years which is about 2.5 times higher
than the effective dose equivalent at the age of 30 years.
On the average. for the age group up to 10 years theeffective dose equivalent might be about a factor 1.5-2higher than for adults [J 19]. This correction factor refers
to the quotients of effective dose equivalent to exposure
given in Table 21.

B.

LEVELS AND DOSES(31)

INGESTION

152. Ingestion of water containing dissolved radon
results in a radiation dose to the body from the radongas and the radon daughters in the water. The main partof the ingested radon is eliminated from the body very
rapidly through the lungs. The resultant dose equivalent
has been estimated by several investigators on the basisof experimental studies of exhaled radon following theingestion of radon-rich water [A13. 823, B24, H25. K23,
S17]. The stomach, whole body, liver, kidneys. fat andmarrow have been considered as target organs. The
largest dose is estimated to be received by the stomach.
153. For the stomach the absorbed dose per unit
activity of 222Rn ingested varies between about 50 and
200 nSv Bq-t. Using a weighting factor of 0.06, theeffective dose equivalent per unit activity of 222Rn
ingested is thus 3-12 nSv Bq-1. In general, most of thedaily intake of water is ingested in food and beverages
such as tea and coffee. rather than by direct
consumption. Much of the dissolved radon is released
from water during cooking and boiling and the only
significant radon intake comes therefore from thedrinking of water itself. The amount of water consumed
in this way varies between 0.3 and 1.2 I d-1 [S17].
Assuming a consumption of 0.5 I d-1, and an effective
dose equivalent per unit activity ingested of 3 nSv Bq-1.
a radon concentration of 1 kBq 1-1 leads to an annual
effective .dose equivalent of 0.5 mSv (range 0.3-5 mSv).

RADON ANDTHORON IN OUTDOOR AIR

154. The concentrations of radon and thoron andtheir daughters in air vary with place, time, height
above ground and meteorological conditions. Estimatesof annual averages at different locations requires
frequent sampling over the long term and suchmeasurements are rare. Table 23 summarizes data forradon and 2t2Pb concentrations at various geographic
locations, as given in the references or calculated frompublished data. Some estimates of radon daughtersassume radioactive equilibrium with radon, and this isseldom the case. The equilibrium factor F for radon
daughters (as defined in paragraph 15) is assumed, as inAnnex B of the 1977 report [U6], to be 0.6. The value of
F in outdoor air depends on meteorological parameters
and lower values of F (0.4-0.6) are not uncommon. The
average, value of the ratio of the thoron daughter 212pb
to 222Rn is observed to be 0.06 ± 0.04, and implies athoron daughter activity concentration which is about afactor of 10 lower than for radon daughters.
155. Since the values in Table 23 are not necessarily
representative of the locations concerned, they are noteasily comparable. However, the average values forcontinental, island and ocean air probably are representative. These are 3 Bq m-3, 0.1 Bq m-3 and 0.1 Bq
m-3, respectively. For the estimation of average dose
equivalent, a radon concentration in air over land of 3
Bq m-3 might be used, corresponding to an equilibrium
equivalent concentration of 1.8 Bq m-3. Using thequotient of effective dose equivalent per unit
equilibrium equivalent concentration given in Table 22,
the corresponding average annual effective dose equivalent from radon daughters is 5.6 10-2 mSv, assumingthat 5 hours are spent each day outdoors. Using a
212Pb/222Rn ratio of 0.06, the corresponding averageannual effective dose equivalent from thoron daughters(assuming equilibrium between 212Pb and 212Bi) is 1.8
10-2 mSv.
156. Higher radon and radon daughter concentrations
in outdoor air are likely in the vicinity of coal-fired andgeothermal power stations and uranium tailings. Table
24 presents normalized annual effective dose equivalents from outdoor air for such sources. calculated fromequations (19) and (20) using the dose conversion
factors given in Table 22. An equilibrium factor of 0.6
and a value of 0.2 for the fraction of time spent
outdoors were assumed. The radon dispersion coefficients used are illustrated in Figure XVIII. Normalized
release rates of 60 GBq (GW a)-I and 370 TBq (GW a)-1
were used for coal-fired and geothermal stations,
respectively, and a stack height of 100 m was assumed.
It is not easy to provide a clear-cut figure for thenormalized release from tailings because it depends ontheir configuration and surface area. However, taking
the figure of 109 Bq (MW a)-I (Annex F, Table 2) froman area of 0.6 hectare (or an exhalation rate of 5.3 Bq
m-2 s-1). Table 24 gives normalized annual effective
dose equivalents for tailings areas of 104 and 106 m2,
respectively. To estimate the total radiological impact,
the values in Table 24 should be increased by about afactor of 3 to include the effects of indoor exposure.
B.

RADON IN WATER

157. Measurements of radon in water have mostly
been associated with the study of correlations between
uranium/radium concentration in rock and radon
concentration in ground water. In general. they have167

been undertaken only in uranium-bearing areas, orregions with a known high concentration of radon in
the water. Measurements intended to estimate theweighted average radon concentration in water for acountry or community are rare, because radon in water
has not been considered to be a significant factor forhuman exposures, except in areas with very high radonlevels. However, the recent interest in radon exposurein houses has indicated radon in water to be a potentially significant source in some cases. The results ofsome measurements of radon in water are shown in
Table 25 and more extensive data may be expected in
the future. It must be emphasized that surface water inmany countries is the mean source of drinking waterand this water is normally expected to have low radon
concentration.
158. The data presented by Hess [Hto] for the UnitedStates are probably not representative, and perhaps noteven for the counties examined. Most of the wells were
drilled artificially and selected with special emphasis on
granite and pegmatite areas where high radon concentrations were expected. The measurements follow
approximately a log-normal distribution. The resultsfrom North Carolina [Sl] include only those water
samples with statistically significant activity concentrations of radon ( > 700 Bq m-3), without mention of thenumber of values discarded. Other studies of radon
concentrations in the United States have been reported
for water samples from North Carolina [Al], Western
United States [01), Hot Springs, Arkansas [K15], Great
Salt Lake, Utah [T2) and South Texas [G7]. The results
were presented as examples of high values of radon inwater supplies. Of these water sources 74% had a radon
concentration of less than 74 kBq m-3 and 5% above
370 kBq m-3 [D14].
159. The results from Finland in Table 25 refer to 192
drilled wells. These include recent results together withother extensive measurements [A7, C4, All, K18]. A
summary of data is given in Table 26 and in Figure
XXX. The results are found to follow a log-normal
99

distribution. The population-weighted average is 56
kBq m-3. which must be considered as a relatively highvalue.
160. The Swedish data represent water from almost allwaterworks, delivering more than 105 ml of groundwater per year to about 3 million people. In addition,
3.7 million people in Sweden use surface water fromwaterworks and the rest, about 1 million people. use
private wells. If the weighted average of the radon
concentration in private wells is assumed to be 10-100
kBq m-3 [Sl 1], the weighted national average is 10-20
kBq m-l.
161. In the United Kingdom natural radon levels inwater supplies are lower than in many other countries[H9]. Two extensive surveys carried out in the early
1960s [TS, K6] found the highest radon concentration(26 kBq m-3) in a reservoir on granite. However, inhighly mineralized granite areas (Cornwall and Devon)
the radon concentration in some water sources used forsupply is about 700 kBq m-3, Various spa waters haveup to 70 kBq m-3.
162. A report from the Federal Republic of Germany
summarizes the concentrations of natural radionuclides
in water, food and in man [M18]. For radon in drinking
water the average values lie in the range of 0.4-4 kBq
m-3,
163. In conclusion, available measurements on radonin water cannot easily be used to estimate weighted
mean values for a country as a whole. The measurements often refer to areas of special geological interest,
because of their high content of uranium or radium orof special radiological interest because of their highradon levels. It seems likely that only a small
proportion of the world's population, perhaps between
1% and 10%, consumes water containing concentrationsof radon of the order of 100 kBq m-3 or higher, drawn
from relatively deep wells. For the remainder who
consume water from wells or surface sources, theweighted world average concentration from all sources
is probably less than 1 kBq m-3. A small proportion( < 1%) consumes water containing 1-10 MBq m-3 ofradon, and there have been a few exceptional reports ofconcentrations in the range 10-100 MBq m-3.

90

164. The radiation dose caused by radon in water isdue partly to ingestion and partly to inhalation of theradon daughters produced by decay of the radon. The
relevant annual effective dose equivalents from watercontaining 1 MBq m-3 of radon are 0.5 mSv (ingestion),and 6 mSv (inhalation of radon daughters). The lattervalue can be calculated from the relationships given inparagraphs 96 and 136 and in Table 22. If one assumes
a value of 3 kBq m-3 for the average radon concentration in water, the corresponding annual effective
dose equivalent is about 20 µSv.

~>g

B.... 50

...

er

u

JO

<

20

...==..,
::,
:,:
::,

'-'

10
5

i

.i

C.

0.L

0.01

0.1

,o

RADON CO!IC U:TRA T l OIi ( HBq m- J )Figure XXX. The distribution of radon concentrations
In (1) bored wells In the Helslnkl area: (2) bored wells
In Finland outside Helslnkl; (3) other walls In Finland(excluding waterworks) [A7, C4]168

RADON IN HOUSES

165. There is at present considerable interest in thisarea, particularly in the light of domestic energy conservation programmes. Radon concentrations in thedomestic environment are also being affected by the useof land fill and of building materials which haveradium concentrations significantly above normal. The
following paragraphs summarize available data but it isexpected that many new data will emerge in the literature from current studies.

(a)Austriahouses sel~cted at random in 19 Canadian cities, andmeasured m 1977, 1978 and 1980. The sample corresponded lo about 0.4% of the houses in the cities
studied. Basements (or ground floors in houses with nobasement) were the preferred sampling locations. The
houses were regarded as typical for Canada, made withwood frames and little stone. Interior wall linings ofpainted natural gypsum were common and were foundto be an insignificant source of radon. Results are
summarized in Table 27. The average equilibrium
equivalent concentration of radon is 17 Bq m-3, corresponding to an annual effective dose equivalent of
1 mSv. Since the measurements were performed insummer periods, the annual average might in fact behigher. Radon appeared to originate from radium innearby soil. Geographical differences were statisticallysignificant. Variations within cities were however
generally greater than variations between cities. The
equilibrium factor calculated from the geometric means
is on the average 0.52 ± 0.12. The results of all
measurements show a log-normal distribution, which isillustrated in Figure XXXI.

166.
Extensive measurements of radon, thoron andtheir decay products have been made in Salzburg,
Austria [S22). To obtain representative values a numberof test families and individuals were assessed (729individuals in all). Special efforts were made to correct
for time-variations in the activity concentrations. The
values of radon concentrations were observed to be lognormally distributed. The mean concentrations were
found to be 22 Bq m-3 for radon, 12 Bq m-3 for radon
daughters (an equilibrium factor of 0.56 was used,based on reported mean radon/daughter ratios) and1 Bq m-3 for 2t2Pb. Maximum concentrations weremore than a factor of 10 higher than the average. The
reported radon daughter concentrations correspond toan annual effective dose equivalent of 0.7 mSv.

(b)

Canada167. An extensive survey was recently reported from
Canada [M6, M26]. It concerned a total of 13 436

..,
'e

g

4

a,

3

0

..J

0

5

10

20

30

40

50

60

70

80

90

95

98

99

CUMULATIVE FREWENCY ('-')

Figure XXXI. Log-normal cumulative frequency plot of radon daughter concentrations
In Canadian homes (1977, 1978, 1980 surveys)

168. In March Township, Ontario, Canada, 343
houses were surveyed because of the discovery of
nearby low-grade uranium deposits (5 ppm ofuranium). Based on radon daughter measurements.
56.6% of the houses had equilibrium equivalent concentrations of radon lower than 19 Bq m-3, The highest
value was 700 Bq m-3 and the arithmetic average was
50 Bq m-3 [L7. T8].
169. The area of Castlegar-Trail in British Columbia.
Canada, has been surveyed because of high radon
concentrations in water. Based on radon daughtermeasurements, 46.2% of lhe homes had equilibrium
equivalent concentrations lower than 19 Bq m-3; thehighest value observed was 2900 Bq m-3 and theaverage was 74 Bq m-3 [L7].
170. Other investigations have been made in Canada[K9) in areas where radioactive contamination was
suspected for various reasons in radium-uranium refineries, metallurgical operations making use of refinery

residues and uranium mining. One area was classified
as a "normal" reference area. The results are shown in
Table 28.
171. The influence of radon in water on the levels ofradon and radon daughters in houses was studied in asurvey in Canada including 6 houses, 5 trailer-homes
and 2 schools. The water supplies originated from
15-62 m deep wells in granite. The results are seen in
Table 29 [M7]. The air-to-water concentration ratio (seeparagraph 96) is small (average 2 1Q-5), probably
because of good ventilation. The low equilibrium
factors F support such a conclusion. Table 30 shows theresulting increase of radon concentration in air due to awarm water shower with water containing 4.4 kBq m-3
radon [M7]. The decrease of the radon concentration
after the shower corresponds to a ventilation rate of 1-3
h-1 and the radon daughter concentration increases
only to about 10% of the equilibrium value. The air-towater concentration ratio is (2-8) JQ-4 in this case.
169

{c)

Finland172. Between 1977 and 1978 a preliminary survey onradon and radon daughter concentrations in 35 normal
Finnish dwellings was carried out in the Helsinki area
[M20]. Buildings of different ages, types and building
materials were included. The radon concentration in
tap water was below 100 kBq m-3 and therefore it was
concluded that the main sources of radon were thebuilding materials and the soil. The mean equilibrium
equivalent concentration of radon during the day was
13 Bq m-3 and the radon concentration 27 Bq m-3. The
24 h mean value of radon concentration was 44 Bq m-J
and the equilibrium equivalent concentration of radon
17 Bq m-3, corresponding to an annual effective dose
equivalent of 1 mSv. The survey included too many
concrete houses and too few wooden ones for the mean
to be regarded as representative of radon concentrations in Finnish dwellings. Later measurements in thesame area with integrating-type instruments gave higher
mean concentrations. This is believed to be due at leastin part to higher concentrations during the night thanthose estimated in the first series of measurements. The
highest concentrations (up to the level 10 OOO Bq m-3)
were found in houses where the only contributor can beradon from the ground or bedrock.
173. Radon in water may be a significant source ofradon to air in dwellings in many countries. In theregion of Helsinki, Finland, very high radon concentrations in water have been reported [C3, K 1, K2]. The
highest concentration measured was 44 MBq m-3. In a
recent study, radon measurements in air were carriedout in 20 houses with radon concentration in water
between 150 kBq m-3 and 17 MBq m-3. The rooms in ahouse were classified according to the use of water. The
results are given in Table 31 [A3J.
174. The table shows that the radon concentrations
were sometimes remarkably high and, as expected,
higher in rooms and situations where water was used(bathrooms, etc.). Under such conditions it is expectedthat the equilibrium factor F is smaller than average.
The air-to-water concentration ratio was found to be
the following in the three groups of rooms: (21 ± 9)
· J()-4 in wet rooms; (6 ± 3) 1()-4 in ordinary rooms withwater; (0.6 ± 0.3) lQ-4 in living rooms, etc. (900/o confidence level). A weighted average value would be
1.4 1Q-4, assuming 0.5 h spent in wet rooms, 2 h in
ordinary rooms with water and 17 h in other rooms.
Using an equilibrium factor F of 0.5 (which may be aslight over-estimate), and average values for the radon
concentration in water and for the air-to-water concentration ratio, the weighted equilibrium equivalent radon
concentration is 360 Bq m-3. The maximum value
would amount to 1200 Bq m-3. The results of afollow-up study [A4] are within the range of the abovementioned values. The air-to-water concentration ratios
are higher and much more variable for wet rooms (IQ-4
to J0-2) than for living rooms. Measurements of radon
daughters by track-etch dosimeters carried by persons
during three-day periods give a ratio of equilibrium
equivalent radon concentration to radon concentrationin water of (0.4 ± 0.3) 1Q-4.

ventilation rate of 0.5 h-1 are estimated from themeasured exhalation rates. The results arc summarizedin Table 32. Mean values for radon and thoron are 8.1
Bq m-3 and 0.37 Bq m-3, respectively, corresponding toannual effective dose equivalents of 0.5 mSv and 0.1!11S~. Other measurements [J 15) on about 250 dwellings
md1catc a log-normal distribution with geometricmeans equilibrium equivalent concentrations of 7-18
Bq m-~ and 0.3-0.6 Bq m-J for radon and thoron,
respectively.

(e)

176.
A study has recently been made in Norway of
the radon concentrations in 129 dwellings in the areaaround Oslo [S24] (see Table 33). Radon daughtermeasurements were made in 25 dwellings to estimate
the average equilibrium factor F which was found to be
0.5. Extensive measurements were made to study theeffects of ventilation and changes in barometricpressure and the emanating power of some building
materials.
1~7. The measurements were carried out during thewmter of 1977-1978. The radon concentrations were
found to be dependent on radium concentration andporosity of the building material and on radon exhalation from the ground, but were even more dependent
on the ventilation and the atmospheric pressure. It
appeared of special interest to evaluate the influence ofventilation on radon concentration during the winterseason, when the ventilation rate is relatively low
because of energy conservation efforts. The distributionof people living in various types of houses was assumed
to be 20% of the people in wooden buildings, 5% inbrick bu_ildings and 75% in concrete buildings in the
Oslo region. Over the whole country the corresponding
values are 75%, 3% and 22%.
178. The distribution of radon concentrations (seeTable 33) was approximately log-normal. On average,
wooden houses had higher radon concentrations thanbrick houses, an observation explained by the fact thatwooden houses in Norway are mostly one- or twostorey buildings for which radon emanation from theground can be expected to be of greater significance.
179. The data on the distribution of radon concentrations in houses in the Oslo region, combined with thedata on the distribution of houses of different building
materials in Norway, lead to an average radon concentration of 52 Bq m-3. It it is assumed that theequilibrium factor is 0.5, the equilibrium equivalentconcentration of radon would be 26 Bq m-3, corresponding to an annual effective dose equivalent of 1.6
mSv. However, this may be too high an estimate for thewhole country, as gamma-ray measurements in Norway
indicate that the natural gamma-radiation backgroundis relatively high in the Oslo region, compared with themean value for Norway.

(j)

180.

(d)

Germany, Federal Republic of

175. Measurements in the Federal Republic of
Germany have recently been published [W14). The
study covers 32 houses, grouped according to theirprincipal construction material: equilibrium equivalentradon and thoron .concentrations, normalized to a
170

NorwayPolandData on radon and radon daughters activity
concentrations in flats in Poland have been reported[013]. The results are summarized in Table 34. The
radon values were given as maximum values and thesignificance of the weighted average as a representativevalue for the flats is therefore uncertain. Other data on
measurements in dwellings indicate higher averagevalues. From measurements in Pulawy, Czestochowa

and Warzaw in the Ursyn6w district an average
equilibrium equivalent concentration of radon isestimated to be 17 Bq m-3 (equilibrium factor = 0.5)
[B 16. B17], corresponding to an annual effective dose
equivalent of I mSv.
(g)burning. There are therefore many tailings piles fromthis production, the number and location of which are
not yet known. Some of them have been used as
housing areas. Measurements have been carried out inone such area, outdoors and in houses built on thetailings [S34]. It has been estimated that 200 to 2000
houses may have been built in such areas [S29].

Sweden181.
A number of measurements have been carriedout in Sweden [S35]. Following measurements made by
Hultqvist in 1956 [H17] in about 300 dwellings built
before 1946, radon in houses was not considered amatter of serious concern in Sweden until the last few
years. The main reason for the recent change in attitudeis the continuing tendency, in the development ofbuilding standards, to lower ventilation rates and to
improve the airtightness in order to conserve energy.
The ventilation rate in houses built during the years up
to 1950 was 0.8 ± 0.5 h-1 in apartments and 0.9 ± 0.5
h-1 in detached houses. During the 1950s the ventilation
rate in new dwellings was 0.6 ± 0.2 h-1 and 0.8 ± 0.2
h-1; during the 1960s 0.5 ± 0.2 h-1 and 0.6 ± 0.2 h-1;
and during the 1970s 0.3 ± 0.15 h-1 and 0.45 ±. 0.45h-1; in apartments and detached houses, respectively.
This decrease in the ventilation rate causes an increasedradon concentration in houses. Furthermore, more
people live in apartment houses now ~han previously
and modern detached houses contam more stonematerials than older houses.
182. Up to 1975, a common building material was
aerated concrete containing alum shale. This material
contains more radium than other building materials
and this has given rise to an increased exposure to
gamma radiation and radon daughters. It is estimatedthat between 350 OOO and 700 OOO dwellings in Sweden
contain aerated concrete based on alum shale. Of these.
between 3000 and 20 OOO are estimated to have radon
daughter concentrations in indoor air requiring further
investigation.
183. The radium concentration in this material varies
as does the use of the material in the houses. From an
investigation made in 1956 [H17] the average
equilibrium equivalent radon concentration in . thesehouses was estimated to be 58 Bq m-3. The maximum
value was about 5 times higher and the distribution ofradon daughter concentrations was found to be ~~redependent on the ventilation than on the activ1ty
concentration in the building material.
184. However. some houses have been identified withan unusually large fraction of concrete based on alum
shale in their building material. Measurements onradon and radon daughters have been made in 32
single-family houses where that is the case. The results
are shown in Table 35 [S45]. The average of the radon
daughter activity concentrations measured in all houses
is 260 Bq m-3, expressed as equilibrium equivalentconcentration of radon. However, whether this averagevalue is really representative of the true average is
uncertain. There are reasons to believe that it may be an
overestimate [S45].
185. In Sweden an unusual environmental situation
has recently been described. Alum shale exists in many
areas of central and southern Sweden and it has beenused since the sixteenth century and up to the 1930s forthe production of alum. It was also used for lime-

186. The radium concentration of the tailings was on
average 2900 Bq kg-1. The gamma radiation dose rate
in air above reclaimed areas was about 0.4 µGy h-1 andabove unreclaimed areas about 1 µGy h- 1. In recreation
areas the dose rates were 0.9-2.4 µGy h- 1. The radon
concentration outdoors was 45-70 Bq m-3 at the time of
measurement and the radon concentration in drinking
water was about 10 kBq m-3. Measurements werecarried out in 7 single-family houses. The averageradon concentration was 860 Bq m-3 (range 430-2100
Bq m-)) and the equilibrium equivalent concentrationof radon was 500 Bq m-3. The ventilation rate was low(0.09-0.28 h-1) and was in fact lower than the current
Swedish standard (0.5 h-1). If the ventilation rate wereincreased to 0.5 h-1, the average radon concentration
would be about 400 Bq m-3, corresponding to an
equilibrium equivalent concentration of rado~ of 200
Bq m-3 with an equilibrium factor of 0.5. provided th~t
the increased ventilation rate does not cause a drop Illpressure, which might effect the exhalation rate fromthe ground below.
187. In order to estimate the overall average radon
daughter concentration in homes in Sweden,
measurement of radon and radon daughters, gamma
radiation, activity concentration in building material
and of ventilation rates are being carried out in"typical" houses. The results are to b·e combined withother results on activity concentration in building
materials, gamma radiation in houses, distrib~tion ofvarious ventilation systems and building materials, andvariation of building practices with time. One part ofthe investigation includes 63 "typical" dwellings
selected from seven types of houses built at the
beginning of the 1970s in the town of Gavle in central
Sweden. The results of the investigation are presented
in Table 36 [E2].
188. The measurements on radon and radon
daughters in houses in Sweden continue ~nd new
results indicate that the greatest problem 1s radon
emanating from the ground. Houses have been foundwith more than 10 OOO Bq m-3 of radon and it isestimated that about 75% of the total collective dose
caused by inhalation of radon daughters depends onradon from the ground.
189. The estimated average radon concentrations for
all homes in Sweden (dwellings existing in 1950, 1975
and estimates for 1985) are presented in Table 37 [S35].
Later recalculation has shown that the value for 1975 isprobably underestimated by about 50% because oflower ventilation rates than assumed. Recent measurements in 600 houses representative for Sweden indicate
an average value for radon daughters o[ _60. Bq m-3 _in
1980. The national average of the equihbnum equivalent concentration is believed to lie within theextremes of 40 and 140 Bq m-3. Therefore, the value for1985 is probably also an underestimate. The values of
the radon daughter concentrations are log-normally
distributed. A concentration of 60 Bq m-3 corresponds
to an annual effective dose equivalent of 3.7 mSv.
171

(h)

United Kingdom

190. A wide-ranging survey in the United Kingdom
has been reported [C6]. The measurements were carriedout in 87 dwellings in England and Scotland varying inage from one to 300 years. They were in the main
single-family houses made of clay brick, many withconcrete floors at ground level. Measurements weremade of the activity concentration of 21spo and fromthese measurements, together with determination ofventilation rates, the radon exhalation coefficients (secparagraph 34) were calculated. Because the exhalation
coefficient is practically independent of the ventilation
rate within the range of variation occurring in houses, it
was possible to calculate the radon daughter concentrations corresponding to an average ventilation rate in
the houses, assumed to be 1 h-1.

191. The median value for radon exhalation coefficient was found to be 11.8 Bq m-3 h-1 and the arithmetic
mean was 22.2 Bq m-3 h-1, with a range from 0.44 to 204
Bq m-3 h-t. By excluding the extreme maximum value
from a rather uncommon type of dwelling the arithmetic mean was reduced to 20 Bq m-3 h-1. (The exhalation rate expressed in units of Bq m-2 h-1 can be
arrived at by dividing by 2 m-1, which is the appropriate value of the expressioni.

where S is the surface

of walls, floors, etc., and V is the volume of rooms.)

192. Assuming an average ventilation rate of 1 h-t andpaying due consideration to the radon concentration in
the outside air-assumed to be 3 Bq m-l-the average
equilibrium equivalent radon concentration in thehouses was found to be 13 Bq m-3. That corresponds toan annual effective dose equivalent rate of 0.8 mSv. The
cumulative frequency distribution of dose from radon
decay products is shown in Figure XXXII.

(i)

194. The distribution of radon and radon daughter
activity concentrations has been investigated over a
two-year period in 21 New Jersey and New York
residences [G 1]. Most of the buildings were singlefamily, of one or two stores, and of wood frame orbrick construction. The geometric mean of theequilibrium equivalent radon concentration was 15.2
Bq m-3, and the arithmetic mean 16.3 Bq m-3 (range 2.6
to 107 Bq m-3) corresponding to an annual effective
dose equivalent of 1 mSv.
195. Radon daughter concentrations in houses on
phosphi1te-related land in Florida have been reported[U4, U8]. There are 1000-3000 houses built on
phosphate lands and a classification of buildings andtheir equilibrium equivalent radon concentrations
based on radon daughter measurements in Polk County
are sho'wn in Table 38 [US). In Colorado some waste
products from the uranium industry have been used asfilling material under a number of houses causing anenhanced radon concentration indoors. The radium
concentration in this material was 4400 Bq kg-I on
average. Table 39 shows the distribution of equilibrium
equivalent radon concentration in some of these houses[Cl 1]. The average value estimated from the table isabout 200 Bq m-3; the weighted average for a
population of 15 OOO is about 37 Bq m-3, corresponding·to an annual effective dose equivalent of 2.3 mSv.
196. High radon concentrations have also been foundin houses having unpaved crawl spaces. In a total of 22
houses investigated in the Chicago area, the radon
concentration was more than 185 Bq m-3 in nine houses
and six of these houses had more than 370 Bq m-3. The
highest values were about 1000 Bq m-3. The radon
emanated from the unpaved crawl space under thehouse and the exhalation rate was about 0.3 Bq m-2 s-t.
The radium concentration in the soil was normal (about
40 Bq kg-1) [R12].
U)

100

10

...
...u
I!:
...""
>

1.0

United States

Yugoslavia

197. In the neighbourhood of uranium ore deposits in
Yugoslavia, radon concentrations have been measured
in houses, some of which were built of stone from theuranium area [K20]. The concentrations were in therange of 30-100 Bq m-3. All measurements were madein the daytime and because the radon concentrations
were found to increase during the night the reported
values underestimate the average by approximately afactor of 2. The radon concentration outdoors varied
between 4 and 8 Bq m-3 .

..J
c(

:::,

~
<

0.1 .___ _.................' - - - ~ - - - - ~ - ~ - 99.99
9 9
~o
0.01
PERCENTAGE OF DI/ELL !NGS WITH LESS THAN
ASSOCIATED At.NIJAL EFFECTIVE DOSE EQUIVALENT

Figure XXXll. Cumulative frequency distribution ofannual effective dose equivalent from radon decay
products In some dwelllngs In the United Kingdom

193. Phosphogypsum can replace ordinary material inbuildings. The radium concentration of phosphogypsum varies between 20-1500 Bq kg-' (see Annex C).
In a prospective study, the radon concentration inhouses with phosphogypsum (radium concentration 900
Bq kg-1) has been estimated to be about 7 Bq m-3 [03,W20]. The ventilation rate was assumed to be 1 h-1.
172

(k)

Other countries or areas

198. Other measurements were reported in Annex Bof the 1977 report [U6]. There have also been estimatesof the radon daughter exposures in houses, on the basisof the radium concentration in building materials [N2].
Using a model developed by Krisiuk et al. [K 13) andapplying "typical" values of radium concentration inbuilding material (50 Bq kg-I), an emanating power of
0.01-0.04, and a ventilation rate (1 h-1), estimatedtypical values were obtained for the increases in
exposure to radon daughters above outdoor levels. The
results were given in WLM. These results are given inthis Annex recalculated as average values of
equilibrium equivalent concentration of radon. The
equilibrium equivalent concentration for outdoor air isadded, namely 1.8 Bq m-3. These results. together with

those given in Annex B of the 1977 report [U6), areincluded in Table 40.
(/}

S11111111ary

199. The distribution of the radon daughter concentrations in houses is generally log-normal. With the
exception of Sweden, 90% of buildings have concentrations Jess than about 50 Bq m-3. A few per cent may
have values greater than 100 Bq m-3. Sweden seems to
be exceptional with more than 30 % of buildings withindoor radon daughter concentrations above 100 Bq
m-3. The main source of radon is the soil and building
materials (aerated concrete) containing alum shale.
Another reason is the reduced ventilation rate in all
houses over the last few years, as a result of energy
conservation programmes.
200. Besides the general distribution of radon
daughter concentration, there are in many countries
exceptionally high levels because of high radium
concentration in the ground or building materials,
sometimes in combination with poor ventilation.
Extreme values between 1000 and 10 OOO Bq m-3 occur.
The relative number of houses affected by extreme
values ( > 1OOO Bq m-3), such as some in Grand
Junction and Florida in the United States, in Sweden
and the United Kingdom, may be between 0.01 to 0.1%.
The corresponding annual effective dose equivalent is
60 mSv or more.
201. However, the main contribution to the collective
effective dose equivalent may not result from the small
number of houses with elevated radon concentrations.
If it is assumed that the radon daughter activity concentration is less than 50 Bq m-3 for 90% of the people,
50-100 Bq m-3 for 9%. 100-1000 Bq m-3 for 0.9% and1000-10 OOO Bq m-3 for 0.09% and the middle value ineach range is used, the collective effective dose equivalent caused by exposure to radon daughter concentrations of less than 100 Bq m-3 correspond to about 75%of the total collective effective dose equivalent. For
Sweden this estimate is not valid, as a larger fraction of
the population is exposed to high radon daughter
concentrations.
202. The average values of the equilibrium equivalentconcentrations of radon in dwellings in different
countries are summarized in Table 40, where the corresponding effective dose equivalents are calculated using
the dosimetric coefficients given in Table 22. The values
should be considered with some caution, as seasonalvariations are, for instance, not taken into account.
203. It may be seen in Table 40 that with the
exception of Sweden the mean values of the indoor
equilibrium equivalent 222Rn concentration in different
countries cover the range from 5 to 25 Bq m-3. Taking
into account the dose conversion coefficients listed inTable 22, this corresponds to an annual effective dose
equivalent ranging from 0.3 to 1.5 mSv. For the total
population in the temperate regions of the world, 15 Bq
m-3 seems to be an appropriate mean value for theindoor concentration, which is about 8 times higher
than the mean activity concentration in outdoor air (1.8
Bq m-3). This yields a mean annual effective dose
equivalent of about 0.92 mSv from indoor exposure andof about 0.06 mSv from outdoor exposure, giving a
total of about 1 mSv from inhaled 222Rn daughters. Thisvalue refers to temperate regions of the world. For
equatorial regions so far no measurements areavailable. Having regard to the different domestic
conditions, the indoor concentrations of radon
daughters in those regions might be considerably lower
than in temperate regions. For large population groups
this level will be comparable with the normal outdoor
level, leading to an annual effective dose equivalent of
about 0.2 mSv. Taking into account that about twothirds of the total world population is living intemperate regions, a global mean annual effective dose
equivalent of about 0.8 mSv-averaged over all age
groups-from inhaled 222Rn daughters would be
expected (See Table 12 of Annex B).
204. By comparison with 222Rn daughters, very few
measurements of 220Rn daughters have been reported[C6, S21, W14]. However, the simultaneous measurements of 222Rn and 220Rn daughters in houses in theFederal Republic of Germany (see Table 32) and in the
United,Kingdom (see Table 41) seem to indicate a ratio
of about 20 between equilibrium equivalent 222Rn
concentration and equilibrium equivalent 220Rn
concentration. By applying this factor, it can beconcluded that the mean value of the indoor
equilibrium equivalent 220Rn concentration in different
countries should be in the range of 0.2-1.2 Bq m-3. For
the total population in temperate regions of the world amean value of about 0.7 Bq m-3 could be expected.
Taking into account the dosimetric coefficients for
220Rn daughters given in Table 22, this corresponds to amean annual effective dose equivalent of about 0.2 mSv
from inhaled 220Rn daughters. This means that thecontribution from 220Rn daughters to the effective dose
equivalent is on the average about one-fifth of thatfrom 222Rn daughters. For reasons mentioned inparagraph 203, a global mean value of about 0.17 mSv
per year from inhaled 220Rn daughters should be
expected (see Table 16 of Annex B).
D.

OCCUPATIONAL EXPOSURES TO RADON
AND THORON DAUGHTERS
1.

Uranium mines

205. In Annex B of the 1977 report [U6), some data
were reported about radon and radon daughter concentrations in uranium mines and it was noted that the
improvement in working conditions noticed during theprevious years was continuing. This is still the case,although the technical difficulties involved in making
further improvements increase as the concentrations
are decreased. Radon daughter concentrations andexposures in mines in some countries are shown in
Table 42. The value for uranium mines in France in1979 is calculated by using an equilibrium factor of
0.17. By using an effective dose equivalent per unit ofpotential alpha-energy exposure of 8.4 mSv WLM-1 (seeTable 19), the annual effective dose equivalent for
uranium miners is estimated to be 34 mSv in the UnitedStates in 1977, 12 mSv in France in 1979 and 6.2 mSv in
Canada in 1979. The average annual effective dose
equivalent, including the data from India given inparagraph 208, is 15 mSv.
206. The activity concentration of thoron daughters is
not always insignificant. In measurements of radon
daughters and other radiation variables in the presenceof 220Rn at Rio Algom mine, Canada, the representative
average value for radon daughters was 0.084 WL andfor thoron daughters 0.12 WL [B18). Similar measurements have also been made in the Agnew Lake mine,
Canada, and the corresponding values were 0.1 WL for173

radon daughters and 0.09 WL for thoron daughters(B19]. Because the thoron daughter concentration iscomparable to that of radon daughters, special consideration should also be given to the measuring technique[C18].
207. Radon daughter act1v1ty concentration in
open-pit mines and its variation with meteorologicalvariables have been studied at Nabarlek uranium mine,
Australia [L13]. which is a high grade (2%) uranium ore
mine. The radon exhalation rate varied widely but thequotient of exhalation rate to ore grade was in general
fairly stable, about 80 Bq m-2 s-1 per percentage of
U30g. The concentration of radon and radon daughtersin air was strongly influenced by air movements andatmospheric stability and the variations could be up to
an order of magnitude. Normally the radon concentrations were lower during daylight than during the night.
However, during the hours just before dawn the air
frequently becomes still and the radon and radon
daughter concentrations rise to a maximum. The
estimated radon daughter exposure during about half ayear was 0.065 WLM, corresponding to an effective
dose equivalent of 0.5 mSv.
208. Radon daughter measurements have been madein Jaduguda underground mines in India on a regularbasis for many years. The radon daughter exposure has
been estimated for different kinds of operations. The
highest exposures occur most frequently during drilling.
The results for India are presented in Table 43 [R 13,
K 19, A12]. The average effective dose equivalents forthe different categories of mine workers ranged from 14
to 22 mSv in 1979.
209. As a curiosity, the radon concentrations in thewell-known old mines in Schneeberg and Jachymov
may be mentioned. The measurements were performedat the beginning of this century and published in the
1920s [821, L14]. The concentrations were given in"Mache" units, where I Mache = 13.3 Bq. The radon
concentrations in various parts of Schneeberg mine
ranged from 20 to 600 kBq m-3 and the average wasabout 100 kBq m-3. In Jachymov mine the corresponding values were 10-300 kBq m-3 and 100 kBq m-3.
These average values correspond to about 30 WL.
2.

Non-uranium mines

210. Since radon problems in many non-uranium
mines were highlighted during the 1960s and the 1970s.
the radon daughter concentration in these mines has
decreased continuously, as can be seen in Table 44. The
corresponding annual effective dose equivalents are for
Finland (1977) 3.2 mSv, Norway (1980) 3.8 mSv, South
Africa (1973) 14 mSv, Sweden (1980) 5.9 mSv, and for
the United Kingdom (1981) about 1.0 mSv for most of
the coal miners and 22 mSv for miners in other mines.
In a research report on the health effects of radon
exposure in non-uranium mines in Bavaria, Federal
Republic of Germany, the radon concentrations in nine
mines are reported [F7] for the years 1971-1973. The
values reported correspond to potential alpha-energy
exposures between 0.1 and 4 WLM, if an equilibrium
factor of 0.7 is used.
211. Thoron daughter measurements have only been
carried out in a few mines. In two non-uranium minesin Norway the average equilibrium equivalent concentrations of thoron were about 3 Bq m-3 and 20 Bq m-3(84]. In the United Kingdom the mean 2t2Pb concentra174

lions in seven metalliferous mines were 40, 20, 3, 1, 1, 1
and 0.4 Bq m-3 [D6). Accordingly. the equilibrium
equivalent concentration of thoron in mines seems to
be in the range of about 4 to 40 Bq m-3, corresponding
to an annual effective dose equivalent of 0.5 to 5 mSv.

3.

Other occupational exposures

212. Radon exhalation from ordinary rocks and soils
and radon-rich water can cause high radon and radon
daughter concentrations in underground spaces such as
tunnels, hydroelectric power stations, caves, publicbaths and thermal spas. Often an occupational
exposure occurs only for a fraction of the working time
and this fraction is sometimes difficult to estimate.
Table 45 shows concentrations of, and exposures to.
radon dllughters. In some cases the exposures are roughestimates made by assuming a 2000 h exposure peryear; in other instances the real working time has been
considered. The average annual exposures to radon
daughters in spas have been studied over a period of
between 15 and 32 years in the island of Ischia in Italy[B9]. The corresponding annual effective dose equivalents range from 1 to 120 mSv.
213. The levels and distribution of radon concentration have been measured in two calcite caves inJapan, Akiyoshi Cave and Kagekiyo Cave [M23]. The
radon concentration increases by one order ofmagnitude between a point near the entrance and atpoints further away. The average value given in Table
45 (0.8 WL) refers to a point 400 m from the entrance.
Great seasonal variations occur with substantial
increases in the summer; a factor of 500 has beenreported. The value in Table 45 refers to March 1978.
The average radon exhalation rate was estimated to beabout 7 10-3 Bq m-2 s-t and the radium concentration in
the cave wall was reported to be lower than that in thesoil outside the cave.
214. In factories where work with thorium is carriedout (thorium extraction from ore, manufacture of gas
mantles, production of Mg/Th alloys) there is occupational exposure to thoron and thoron daughters. In
some thorium factories in the United Kingdom,
measurements were performed of thoron and thoron
daughters [D6]. In one gas mantle factory extensive
observations were made of the 220Rn: 2t2Pb:2t2Bi ratios,
absolute values and variations of the concentrations.
Since such measurements are rare. they are shown fullyin Table 46. The "inferred values" of thoron are thoseestimated on the basis of the 212pb and 212Bi concentrations. There is little regularity in the activity concentration ratios. probably on account of sharp thoron
gradients in the rooms. The thoron concentrations
given in Table 46 are rather typical of some of the otherfactories examined. Most values are in the range of
1-10 kBq m-3. Other factories had lower values, around0.4-4 kBq m-3. These values are rather similar to others
reported (2-20 kBq m-3) from two thorium plants in
India [M 16]. The average value of all 212Pb measurements in the United Kingdom [D6] was 170 Bq m-3,
corresponding to an annual effective dose equivalent of
about 20 mSv. Some typical variations of the potentialalpha-energy concentration of thoron daughters in athorium factory in India are shown in Table 47 [D10].
The average value is 0.15 WL and the corresponding
exposure is less than 1.8 WLM, corresponding to anannual effective dose equivalent of about 5 mSv.

E.

DELIBERATE EXPOSURES TO RADON

215. For several hundred years radon has been
exploited in "balneology" -the use of spas or baths forthe alleviation of illness. There are balneological facilities using radon in Badgastein. Austria, in Bulgaria, in
Poland and in the USSR.
216. There is a large amount of information about thelevels of radon in 13adgastein. much of which has beensummarized by Uzunov et al. (UlO]; they haveestimated the doses received by the general populationof the town, by the employees of the spa and by theindividuals deliberately exposed to the radon in thecourse of balneological procedures.
217. Thermal springs in the centre of the town supply
radon-rich hot water at a concentration of about 106 Bq
m-3. Annually about 2 ]012 Bq of radon diffuse from thewater into the air, resulting in a mean indoor concentration of about 300 13q m-3 in buildings situated in thecentral part of the town, and up to JOS Bq m-3 in the spa
facilities [UlO].
218. The annual exposures of employees of the spa,
who inhale air with radon concentrations of up to JOS
Bq m-3. are estimated to be between 1 and 40 WLM[UlO], corresponding to an effective dose equivalent of
8-300 mSv.
219. Individuals undergoing deliberate exposure
include children recovering from poliomyelitis andother neurological diseases, who may spend up to
several years in a special children's sanatorium. Theirannual exposure is estimated to be about 0.7 WLM[U10] corresponding to an effective dose equivalent of
about 4 mSv. Adults who breathe the radon-rich air in
the inhalation facilities of the spa are estimated toreceive 0.2 WLM from the standard two-week course,which involves a total exposure time of about fourhours.
220. Uzunov et al. [UIO] conclude their paper with thefollowing statement: "The highly positive effects ofbalneological treatment for man as claimed by balneoJogists are not questioned by us. However. whether
radon represents a necessary and justifiable component
seems to be doubtful. Considering the world-wide
attempts to reduce deliberate irradiation of man byionizing radiation it seems an apparent anachronism to
expose significant population groups, to a large extent,even uncontrolled, to one of the strongest known carcinogens. i.e. the atmospheric alpha emitting radon decay
products."

VI.

ENERGY CONSERVATION ANDLEVELS OF RADON IN AIR

221. In recent years many countries have establishedsignificant programmes to conserve energy. This
chapter will consider the consequences of energy
conservation in terms of effective dose equivalents
caused by inhalation of radon and radon daughters in
the air.
222. Energy conservation in industry means apossible increase in the effectiveness of the use ofmachines and rooms and a decrease in energy
consumption by maintenance and service systems. The
ventilation system may be switched off or used at a
reduced !eve\. in compliance with regulationsprescribed by the authorities. In general. a reduction of
the ventilation rate increases the radon and radon
daughter exposure, unless special countermeasures aretaken. For example, reduced ventilation during nights
and weekends requires consideration of the minimum
time for ventilation before work starts. In mines particularly, the radon and radon daughter concentrations
may increase by several orders of magnitude whenventilation is reduced and several hours of maximum
ventilation may be necessary before work starts [S16]. It
can be inferred from Table 19 that an increase of 1 Bq
m-3 in the average equilibrium equivalent radon
concentration in a mine leads to an increase in theannual effective dose equivalent of about 30 µSv.
223. In houses, energy conservation may involve
reduction of ventilation by sealing of windows anddoors or by reduction of exhaust ventilation. These
measures enhance the radon concentrations approximately in inverse proportion to the ventilation rates (forventilation rates Av > 0.1 h-1). Other procedures which
will influence the radon concentrations are recirculation of the air to reduce the effective ventilation, andthe use of "heat-conserving beds", i.e., the circulation of
air through pieces of rock under the house, which will
enhance the radon concentration because of exhalationfrom the rock [N3, S47]. Similarly, a reduction in theadmission of outside air by a cooling system in a housewill reduce the ventilation rate.
224. The principal methods of calculating theincreased radon and radon daughter concentrations as
a result of decreased ventilation rates in an energy
conservation programme will be given for houses. The
radiological impact is expressed as the excess collective
effective dose equivalent (man Sv). Decisions on energy
conservation may relate to existing houses or new
houses and practical energy conservation programmes
may be different in these two cases. However. themethods of calculation of doses with and without adefined energy conservation programme are inprinciple the same in both cases.
225. To estimate the radiological impact. thedifference has to be calculated between the collective
doses before and after the programme has beenrealized. As the ventilation decreases from A.v 1 to Av2(h-1) the radon activity concentration increases from
Xa.Rn.l to Xa,Rn,2 (Bq m-3) according to the formulae

A/vXa,Rn,1 = ~(33)(the small correction required by a normal radon
concentration outdoors has been neglected)
A/V

Xa, Rn, 2 =A.vi

A Avt - Avz.!\x.,, Rn = V

A.v1 A.v2

(34)

(35)

where A/V is the source term (Bq m-3 h-1) includingradon emanation (Bq h-1) from building materials, theground under the house, and releases from water andgas as seen in equation (21 ).
226. The number of people exposed are grouped
according to the type of house (source terms and venti175

lation) and, after measurements or calculations of
average radon and radon daughter concentration inthese types of houses, the collective dose can be
estimated. As can be seen from equation (35), as long as
the source term remains constant and does not change
as a consequence of an energy conservation
programme, the change in radon concentration
depends only on the ventilation rates. The radon
daughter concentration (and hence the equilibrium
factor F) will increase because of the decreased ventilation rate. Table 5 shows that the factor F will increase
as Av decreases, if the deposition effect is not taken into
account. An estimation which only takes into accountthe relative increase in the radon concentration will
therefore underestimate the impact of reduced ventilation, as will be shown below.
227. The dose caused by inhalation of radon
daughters in air with radon concentration Xa.Rn is
JcFXa.Rn where Jc is the dose conversion coefficient andF the equilibrium factor. If the ventilation is changed
from Avt to Av2 the increase in the dose will be(36)
If it is assumed that the equilibrium factor is unchanged
and has the value F, the estimated increase in the dose
will beThe ratio ( .6.D}1/( .6.D}2 is a measure of the degree ofunderestimation. For values 0.5 < Av < 1 h-1 and avalue F = 0.5 (as recommended in this Annex.
paragraph 136) the underestimation will be less thanabout a factor of 2.5. The formulae and conclusions
above do not include houses with gas heating in whichcase, as mentioned earlier, the radon release rate will
decrease because of the reduced consumption of gas.
However, as can be seen in Table 13, the relative
contribution of radon from gas may be of little significance.
228. As an example, the radiological consequences ofa proposed energy conservation programme in Sweden
is given [S36]. In Sweden the total electrical energy
consumption (transformation and transfer losses
excluded) was about 45 GW a in 1977. About 10 GW a
was used in dwellings and of that about 7 GW a wasused for heating. Of that, 25% was lost by ventilation. It
has been postulated that significant amounts of energy
could be conserved by reducing the ventilation andimproving the ventilation systems. A decrease in theventilation rate by 0.2-0.3 h-1 has been discussed.
229. By measuring ventilation and radon and radon
daughters in different types of houses and building
materials, it has been possible to estimate the averageradon concentration and collective effective dose equivalents and their change with a change in the ventilation
rate. The calculations have only included houses withnatural draught ventilation systems and those with a176

ventilation rate greater than 0.5 h-1. One alternative inthe energy conservation programme was to reduce
ventilation to a rate not lower than 0.5 h- 1. The resultsof comparing the amount of energy conserved and theresultant increase in the collective doses, are presented
in Table 48 (after recalculation of the values in terms ofeffective dose equivalents and using the dosimetriccoefficients given in Table 22). The equilibrium factor F
is assumed to be 0.5 and unchanged. The values inTable 48 can be compared with the total annual
collective effective dose equivalent from houses in 1975
of about 18 OOO man Sv (8.2 106 persons multiplied by
2.2 mSv a-1), assuming a radon daughter concentrationof 36 Bq m-3 (see Table 37). Assuming that the weighted
average figure of 5.6 man Sv (MW a)-I applies
generally, the relative increase in individual annual
effective dose equivalent per MW a of electrical energy
saved is about 0.03%. The effects of the radon activity
concentration in air in houses caused by an energy
conservation programme is much dependent on local
circumstances. The example given above from Sweden
is relevant only for Swedish conditions because ofexisting high normal radon concentrations and low
ventilation rates. However, energy conserved bydecreasing the ventilation will always increase theradon and radon daughter concentration.

VII.

SUMMARY

230. Radon and thoron are naturally-occurring
radioactive gases, which are products of the uranium
and thorium decay series, respectively. Uranium andthorium occur widely in the environment, in rock, soil,
air, water, building materials, man, etc. Some of theradon and thoron diffuses from the material in which it
is formed, is dispersed in ground water and in air. The
total equilibrium amount of radon in air is of the orderof 101s Bq. The corresponding value of thoron is several
orders of magnitude less. Of the total global inventoryof radon, radium in soil contributes two orders ofmagnitude more than any other source.
231. The decay of radon and thoron and the subsequent decay of their daughters terminates with theformation of stable lead. The radon and thoron
daughters occur in the same media as their precursors.
It takes some time, of the order of one hour, for thedaughter products to reach equilibrium. Because of this,and because of deposition on surfaces, there is often
less than equilibrium amounts of the daughter products
in air and water. The equilibrium factor is a measure ofthis deficit in air. Radon and thoron daughters in air
are predominantly attached to aerosols. A minor part,
normally less than 10%, occur as unattached atoms orions. The relative distribution of attached and unattached daughters in air and the equilibrium factor
depend on many variables, such as the decay constant,the concentration and size distribution of aerosols andthe ventilation rates. Increased ventilation decreases theconcentration of radon and thoron daughters in air.
232. The distribution of radon, thoron and their decay
products in outdoor air depends on the vertical temperature gradient, the direction and strength of the wind
and the air turbulence. Owing to its short half-life,
thoron occurs only within a few tens of metres above
ground, while radon occurs up to an altitude of several
kilometres. The concentration at ground level depends
on meteorological conditions and geographicallocation. Normally a minimum concentration occurs inthe spring and summer and a maximum in the autumn

and early winter. Mean annual values of radon concentration in outdoor air vary between 0.1 and 10 Bq m-J.
The higher concentrations arc found in air above
continental areas and the lower concentrations in air
over arctic areas and above the sea. An average value of3 Bq m-3 over land and an equilibrium factor of 0.6 orless for radon daughters outdoors is probably areasonable estimate. The concentration of 212Pb isnormally about one order of magnitude less than thatof radon.
233. In closed spaces, e.g., a mine or a house, theconcentrations in air of radon, thoron and their decay
products are higher than outdoors. In houses the radon
daughter levels may be enhanced by radon fromradium-rich building materials, landfill, soil andbedrock under the house, radon-rich water and by poor
ventilation. The radon activity concentration in water
varies from practically zero to very high values of theorder of 100 MBq m-3. The radon levels indoors may beenhanced by any of these sources and reach values ashigh as 10 OOO Bq m-J. Normal values of radon
daughter activity concentration indoors are of the orderof 20 Bq m-3. Annual occupational exposure to radon
daughters in mines and other working places underground is generally less than 4 WLM corresponding toan equilibrium equivalent concentration of radon of
about 1000 Bq m-3. In well-ventilated mines theequilibrium factor is low ( < 0.5). In unventilated partsof mines radon concentrations as high as 1 MBq m-J oreven more may occur.

234. Inhalation of radon and thoron daughters leads
to deposition in the human respiratory tract and consequent irradiation. The deposition depends on various
factors, such as the size distribution of the aerosols towhich the daughter products of radon and thoron are
attached, and the fraction of unattached daughters. On
average, the dose to the bronchial basal cell layer in thelung is about 5 to 8 times higher than the dose to thepulmonary region. The effective dose equivalent forradon and thoron daughter exposures may be calculated using weighting factors for the regional distribution of lung dose and the mean lung dose. The
Committee's present estimate of mean annual effective
dose equivalent is 1 mSv and arises mostly from radonin houses. There is little experimental information toprovide a good estimate of the annual effective dose
equivalent from thoron daughters; a value of 0.2 mSv is
tentatively proposed. The radon and thoron daughter
concentrations in air, and resulting doses given in thisAnnex refer mainly to countries in temperate parts of
the world. Taking into account that about two-thirds ofthe total world population is living in temperateregions, a global mean value of about 0.8 mSv per
year-averaged over all age groups-from inhaled
222Rn daughters and of about 0.17 mSv per year frominhaled 220Rn daughters would be expected. Occupational exposure to nrdon daughters in uranium mines
causes average annual effective dose equivalents ofabout 15 mSv, and similar exposures have been encountered in some non-uranium mines.

177

Ta b 1e
. Of 226R a and its dau9hters
Radioactive decal eroeert1es

1rs. rn1

Major radiation energies and intensities
Radionuclide

Historical nameUalf-life

a

MeV

%

Radium

1.6 10 3 a

4.60
4.78

6
94

86

Emanation
Radon (Rn)

3.823 d

5.49

100

218p
84 0

Radium A

3.05 min6.00 -100

Radium B

26.8 min

226R
88 a
t
222Rn

+

y

f3

MeV

%

MeV

,:,

0.186

3.3

0.295
0.352

19
37

46
15
16

·I

0.02%

99.98%t
214Pb
82

218At Astatine
85

- 2 s

6.65
6.69
6.76

90
3.6

Radium C

19.7 min

5.45
5.51

0.012
0.008

I

Radium C'

164 µs

7.69

100

210n
81

Radium C"I

214 1.
83 8
99.98'4 I 0.02%

r

0.67
0.73
1.02
6

?

210Pb
82
t
2108.1
83

- 0.1

1.0
1.51
3.26

23
40
19

0.609
1.12
1.764

1.3 min

1.3
1.9
2.3

25
56
19

0.296 80
0.795 10021
1.31

Radium D

22.3 a

0.015
0.061

81
19

0.047

Radium E

5.01 d1.161 -100

Radium F

138.4 dRadium E"

4.2 minRadium G

Stab le

I

+

48
42
6

4

y

-100%

0.0001%y

1210p 0
84

I

206Tl
81

100

5.305

1. 53

100

I

t
206Pb
82

Radioactive decay eroperties of 228 Th and its dau~hters[ES, L12J
Major radiation energies and i ntens i ties
Radionuclide

Historical nameHalf-life

a

13

MeV

%

MeV

y

%

MeV

%

228Th
90

Radiothorium

1.913 a

5. 34
5.43

27
73

0.084
0.216

1.2
0.3

224R
88 a

Thorium X

3.66 d

5.45
5.68

6
94

0.241

3,9

Emanation
Theron (Tn)

55 s

6. 29

100

0.55

0.1

Thorium A

0.15 s

6.78

JOO

Thorium B

10.64 h

0.239
0.300

43
3.2

+
't

22DR
86 n

+

216p
84 o

+

212Pb
82 ·

+
178

0.331
0.569

83
12

lable 1 , continued
Major radiation energies and intensities
Radi onuc 1ide

Historical name2128.1
83
~

212p
84 o

I
20~,
81
I

t
208Pb
82

a

a

MeV

,,

"'

Thorium C6{).6 rnin

6 .05
6.09

25
10

Thorium C'

304 ns

8. 78

100

Thorium C"

3.05 min

I 36%

64"-

I

Half-life

y

MeV

MeV

.e

I. 55
2.26

5
55

0.040
0.727
1.620

1.1
11.8
2.8

1.28
I. 52
1.80

23
22
51

0.511
0.583
0.860

86

°"

23
12

2.614 100Thorium 0

StableTable

2

Properties of radon[J1, H4, W3 j
Value

Property
Volume of Bq of 222 Rn at IHPBoiling point
Melting point
Vapour pressure at - 144° C- 126.3° C- 111 3° C

99
-

0

C

71°
C
61.8° C

Density at iHP
Coefficients of solubilit~/
at atr.iospheric pressure
in waterat
o° C- 71° C

0.13 kPa
l. 3

kPa

5.3
13
53
100

kPa
kPa
kPa
kPa

9.96 kg m- 3

37° C

0.507
0.340
0.250
0.195
0.167

50° C
75° C
100° C

0.138
0.114
0.106

10° C

20° C
30° C

in glycerine
anilineabsolute alcohol
acetoneethyl acetate
petroleum (liquid paraffin)
xylenebenzenetoluenechloroform
ether
hexanecarbon bisulphideolive oil~/

1.6 10- 20 m3- 61.8° C

at 18° C at o° C
0.21
3.80
4.45
6.17
8.28
7.99
6.30
7.35
9.41
9.20
12.6
12.75
12.82

13.24
15.08
15.08
16.56
23.14
29.00

18.4
20.5
20.09

23.4
33.4

The solubility coefficient or partition coefficient inwater is defined as the ratio ~/~a• where \i and
Xa are the radon concentrations in water and air,respectively.

179

T a b 1 e

3Calculated
anof radon and thoron
uc sPotential alpha energy perRadionuclide

222Rn
218p 0214Pb
214 8;
214p 0atom

unit of activity

Epot.atEpot,at/;\.jMeV

10-12 J

19.2
13.7
7.69
7.69
7.69

3.07
2.19
1.23
1.23
1.23

9150000
3620

17800
13100
0.002

Tota 1 (Rounded) a/

220Rn
216p 0212Pb
212 8 ;
212p 0

20.9
14.6
7.8
7.8
8.78

10 -10 J Bq-1

HeV Bq-1

unit of activity
concentration

10- 6 Wl (Bq m- 3 )-l

14700
5. 79
28.~
21. 0
0.000003

27.8
137
101
0.000016

55.4

34500

3.34

Potential alphaenergy concentration(Cpot)per

266

2.65
1660
0.00532
3.32
691
43100065,640900
0.00000305 0.0000000062

2.34

1.25
1.25
1.41

Total (Rounded) !I

757

4720000.02563320
315
0.00000003
3640!I The total is the sum of the potential alpha energies of the daughters
only.

T a b 1 e

4

Calculated equilibrium equivalent concentration of radon and thoron
as a function of the potential alpha energy concentration Cpot
Radon y_R (Bq m·-eq • nThoran Y·-eq, Tn (Bq m-

2.90 10- 5 (Bq MeV- 1) Cpot (MeV m- 3 )8-1-3
1.81 10(Bq J ) Cpot (J m )313700 (Bq m- WL- ) cpot (WL)

2.L2 10- 6 (Bq MeV- 1) cpot (MeV m- 3 )1.32 10 7 (Bq J- 1) C t (J m- 3 )
275 (Bq m- 3 WL- 1) c::t (WL)

T a b 1 e

5

E uilibrium ratios for radon dau htersand equi i rium actor
or various vent, at1on rates
Ventilation
rate ;\.v
(h-1)

o.o

0.1
0.3
0.5
0.7
1.0
1.5
2.0
3.0
5.0
10.0

180

Equilibrium ratio Xa,j/xa,Rn
218p 0

214Pb

214Bi

1.0
0.993
0.978
0.965
0.951
0.932
0.900
0.872
0.820
0. 732
0.577

1.0
0.956
0.820
o. 729
0.655
0.566
0.473
0.381
0.279
0.173
0.077

1.0
0.913
0.718
0.590
0.530
0.384
0.277
0.195
0.115
0.051
0.013

Equilibrium
factor F
1.0
0.928
0.784
0.689
0.628
0.526
0.436
0.356
0.269
0.182
0.103

Table 5, continued
Ventilation
rate >..V
(h-1)
0.0
0.1
0.3
0.5
0.7
1.0
1.5
2.0
3.0
5.0
10.0

Equilibriun ratio xa,j/xa,Tn
216p 0212Pb

212 8;

1
0.395
0.179
0.116
0.086
0.061
0.042
0.032
0.021
0.013
0.006

1
0.345
0.125
0.067
0.042
0.025
0.013
0.008
0.004
0.00160.0004T a b l e

Equi 1ibrium
factor F
1
0. 391
0.174
0.112
0.082
0.058
0.039
0.030
0.020
0.012
0.006

6

Published values of radon exhalation rates per unit area fW15]

Location !IAustria~

Innsbruck
InnsbruckFranceSaclay (80)
Gennanl, Fed. Rep.
AachenIrelandllub1Ti,~ (4,4)

Soil group

Radon
exhalation
rate
Original
per unit area ref.
(mBq m- 2 s- 1 )Mountain
Mountain
Mountain

20, 9
8.6
19

[22)

Podsolic

15, 14(S50)

Podsolic

17

fI12]

Podsolic

27

[S51)

3.4, 8.8

[M24)

11

fW18]

34 + 3.4
38 + 1118
50
53
21 + 1.9[P16]'.Kl7]
[K17)
[Pl6)
[P16]

15
3.8
6.9
5.0

[M25]
[M25]
'.S52)[S52]

4.8, 13
3.8
7.3

f K22][K22]
r1<22J

11

[K22]

19

(K22)

11

(K22)

11

[K22)

Latosolic
Philipeines
Latosol ic
ManllaUnited States
Desertic
Socorro, New Mexico (10)Desertic
Socorro, New Mexico (6)Deserti c
Yucca Flat, Nevada
Podsolic
Lincoln, Massachusetts (10)Champaign County, Illinois (472) Chernozemic
Chernozemic
Argonne, Illinois (8)USSR
Podsol ic
K, rov ( 36)
Podsolic
Moscow (6)Podsolic
Central European Territory (40)
Desertic
Southwest Kazakhstan (5)Sandy desert (Muyun Kum, Ashkhabad,
Desertic
Dzhusaly) (10,5)
The North (Murmansk, Arkhangelsk)(6) Podsolic
Podsolic
Central European Territory (35)
Leningrad, Moscow, Kaluga reg. Chemozemic
Mountain
The Caucasus (15)Chemozemic
Grozny, Baku, Tbilisi, Adler
Mountain
Middle Asia (10)Desertic
Tashkent, Alma-Ata, Frunze
MountainSouth Ura 1s (5)Podsolic
Sverdlovsk
Mountain
Chelyabinsk
Podsolic

[K21)
[Zl]

'.Wl9)

181

Ta b 1e7

Radon exhalation from rock and uranium minerals

Type of rock

Radiumactivity
concentration(Bq kg-I)

Leptite a/
Aptite (T)Aptite (2)Pegmatite (llPegmat i te (2Uranium minerals
Sample 1
Sample 2
Sample 3
Sample 4
Sample 5
Sample 6
Sample 7

Radon exhalation rate for cores(\Jllq m- 2 s- 1;(mBq m- 2 s- 1)(llq kg- 1))

79
460
280
340
330

0.4
1.2
0.88
5.3
8.3

5 .1
2.6
3.1
15.6
25.2

11000031000081000
72000
4500000
240000
28000

260
780
170
63
190
7.8
10

2.4
2.5
2.1
0.9
0.04
0.03
0.36

~/ The radon exhalation rate from a gallery surface was 7.4 mBq m- 2s- 1.

T a b 1 e

8

Activit concentrations kB m- 3 of 220 Rn and 222 Rn at different de ths
or 1 erent ~ressure con 1t1ons, 19]

Barometric pressure (mb)
Nuclide

Depth
(m}

971

993 1007

222Rn

0.1
0.4
0.9

38
47
64

38
51
67

16
22
43

19
24
45

220Rn

0.1
0.4

120
130

97
120

90
120

87
140

Concentrations

Nuclide182

1028

Ta b 1 e 9
kB m-3 of 220Rn and 222 Rn at different de ths
or dif erent win seee s
[ 19]

Depth
(m)

Wind ~peed at a height of 10m(m s- 1)
1.5

3.3

5.7

7.9

222Rn

0.1
0.4
0.9

36
46
75

26
37
58

20
30
44

23
28
44

220Rn

0.1
0.4

100
120

99
120

74
120

91
150

T a b l e

JOMean activity concentrations of some building materials

Country

Material

Numberofsamples

Mean activity
concentration(Bq kg-l}-2-26_R_a~2~3=2-Th_o_r

Ref.

Comments[N2]

Many sources
Different types
Different types
Adequate sampling
Depends on feed materials
Severa 1 sources
Many sources
Depends on source of rock
Variable composition
Many sources
Average weighted by the
relative production
Average weighted by the
relative production
Conunonly used for house building
Wall cladding material
Typical building material
used in Poland

228rh
Germany, Federal
Republic of

Hungary

Italy

PolandUnited Kingdom

United States(exceptional
values}Building sand and gravel
GraniteBricks (traditional constituents}
Pumice-aggregate concrete blocks
Slag-aggregate concrete blocks
Portland cement
Natural gypsum
Chemical gypsum (phosphogypsum)
Red mud bricks
Fly ashConcrete

50
32
109
31
9
14
23
33
23
28
95

< 15

100
59
74
152
< 26
< 19
555
281
~11
13

81
67
81
100
< 19

[N2l

< 11
< 19

[N2]

Brick

176

56

48

[T7]

129
122
241
218
63-610 33-320
19-460 22-590
26-740 11-44
19-22 22-44
7.4-15 <4-7.4
7.4-26 11-67
3.7-19 <4-15(N2l

Lithoid tuff (tufo litoide, Monte Cimino} Nenfro (a variety of tuff, Tuscania)
Fly ash106
Slag42
By-product gypsum
4
Red brick3
Silicon brick3
Cement4
Soil
5
Granites
Sand and gravel
CementClay bricks
White bricks (autoclaved flint andquicklime)
Natura 1 gypsum
Lightweight blocks various aggregates
Phosphogypsum from sedimentary ores
Phosphate land fill, Florida

< 19

233
130
11

89

81

4

7

25

22
52

18
44

5

4

5

7

10
6

73
10
60

22

7

59
629
740

26
18

Gypsum from Florida phosphate rock

1221

10

Uranium mine tailings

4625

'N2l
'.N2

[r,2

fN2 1

tr12!

[N2]

[N2]
[T7)

[N2

[P4]
[P4]
(P4]
[P4]
[P4 J
· [P4]
[P4]
'H21
'.02]
[02 J
;tt2]
[H2 '.

Inadequate samp 1i ng
Inadequate sampling
Inadequate sampling
Sampling probably inadequate
Aggregate may vary

[H2]
[H2'.
[02]
[U2]

Adequate sampling
Inadequate sampling
Depends on ore source
Estimate depends on geologicalstructure and reclamation
procedure[U3] Samples from several processing facilities[Cll] Personal assay of complex
situation183

Ta b 1e

11

Mean activitt concentrations of some buildin9 materials in Nordic countries(Bq kg-l)

Building material

No. ofCountry samples
Min.

Brick

Denmark
Finland
NorwaySwedenBricks of limestone Denmark
FinlandSwedenConcrete
Denmark
Finland
NorwaySwedenCementDenmark
Finland
NorwaySwedenConcrete ballast
Denmark(gravel, shingle Finland
macadam)SwedenAerated concrete
Denmark
based on sandFinlandSwedenAerated concrete
Denmark
based on alum
Swedenshale a/Aerated concrete
Swedenbased on alum
shale b/
Plasterboards
DenmarkNatural gypsum
SwedenPhosphogypsum
SwedenGypsumNaturalDenmark
Finland
NorwayPhosphogypsum
Finland
Light-weight
Denmarkaggregate
NorwaySwedenS1ag aggregate
Finlands~1edenInsulation material Denmarkwoo 1 of stone
Finlandor glass
SwedenTile
Finland
Fly ashDenmark
Wood
FinlandClinker
Denmarka/b/

184

In production 1929-1975,
In production 1974-1979.

232Th

226Ra

Aver.

Max.

Min.

42
80
63
96
8
22

86
134

21
37

Max.
58
91

620

18
49
35
670
1300

2620

34
62
74
127
100
7
4
18
23
4
8
13
9
28
37
21
36
56
80
4
12
8.5 22
19
24
40
4
13
1.6 39
3
72
10
31
36
4
42
53
30
67

12

320

466

560

24

7
8

6

10
4
27

13

4

9

I

7

10

79
37
18
12
5
3
3
6
12
137
14
6
9

4
16
107
266
306
2
2
24
2
70

23
37
41
6
20
7
13
50
11

32
9
20
20
4
7
7

45
7

I

I

6

4

I

2
4
3
12
6
3
2
5
2
3
5
10
2
13

24
36
135
88
84

8.9
II

63
110
0.3
22

10

16
61
28
47
20
44
30
41
19
34
48

7
11
178
40
51
170
102
118
40
19
13
78
150
0.4
66

152
11

25
15
24
80
37
58
30
84
168
95
146
167
53
130

Comments

Aver.

43

195
113
151

153
32
114

29
15
91
210
0.5

4.6
15
32
74
0.2
22

330

108

Adequate sampling
Adequate sampling

115

[Ul)
[M21)
[S41]
Inadequate sampling[S42]
Adequate sampling[Ul)
Inadequate sampling[M21)
Inadequate sampling:s42J
Inadequate sampling
[Ul]
[M22]
Standard deviation 38% [S4!]Inadequate sampling[Hl]
Adequate sampling[Ul]
Inadequate sampling(M21J
Inadequate sampling[S23 J
Adequate sampling(Lll,S42]
Adequate sampling[UJ]
Adequate sampling(M21;
Adequate sampling[Hl]
Inadequate sampling[Ul]
Inadequate sampling(M21 J
Adequate sampling(S42]
Swedish origin(Ul)
Adequate sampling
[S42)

30

37

Adequate sampling

(S42]

4
1

6
12

Adequate sampling
Adequate sampling
Inadequate sampling

[Ul)
[S42]
(S42)

4

Adequate sampling
Inadequate sampling
inadequate sampling
Inadequate sampling
22
Inadequate sampling
51
Inadequate sampling
Inadequate sampling186
l nadequa te sampling
94
182
Inadequate sampling
Inadequate sampling
13
Inadequate sampling
Inadequate sampling
15
Inadequate sampling64
Adequate sampling160
1.2 Inadequate sampling
73
Inadequate sampling

(Ul]
[M21]
[S23)

178
11
29
10
17
42
54
105
21
55
81
56
226
463
40
155

65
4
1.5
3
3.4
37

Ref.

12
45
56
164
69
148
40
8.9
15
46
90
0.7
55

4

[M22 '.

[UJ]
[S42)
[S42]
[M21J
[Ul]
[U!)
[M21 J
[S42J
[M21]
[Ul]
[M21]
[Ul)

Table12Radon concentration in natural gas at the well(Ila, S43, JB, GlB, w21]
Radon concentration(kBq m- 3 )Location of well

Average
CanadaAlberta
British Columbia
Ontario
Germany, Fed. Rep. ofIndonesia
Borneo, Ampa field
Netherlands
Slochteren
Other fields
Nigeria
Niger delta
United States
Colorado, New Mexico
Oklahoma, Kansas, Texas
Texas Panhandle
Colorado
Project Gasbuggy area
California
KansasWyoming
Gulf Coast (Louisiana,
Texas)
California, Louisiana,
Oklahoma, Texas
North Sea
Leman field
Indefatigable field
7 streams supplying
United Kingdom

Ta b l e

2
18
6

Range
0.4-8
14 - 20
0.15-30
0.04-0.4
0.06-0.12
0.044-0.10
0.14-20.034-0.11

0.9
4

0.9
0.6

0.2-540.4-190.4-2
0.04-44

0.4
0.2
0.04-40.07-0.14
0.08
0.03

0.01-0.04

13

The relative significance of different radon sources
1n a reference house

SourceRadon emission
per unit 1 time
(kBq d )Comments

Building materials
and soil underthe buildin#1
Water

60

Exhalation rate 2 10- 3 Bq m- 2s-l

4Outside air

10

m3 d-l and 4 kBq m- 3 , 100 %releaseRadon concentration outdoors-3
4 Bq ~l , ventilation rate
0.5 h

Natural gas
LPG

3
0.2

~/

In some houses the soil may be the dominating source.

185

T a t., l e

14

Descririon of the test sites in private andpub 1c buildings 111 Innsbruck, Austria
[S21J

Test
site
tlo.

Building
material

Purpose of thetest site

Distancefrom theground

Time
(d)

(m)

6
7

Control station:cellarControl station:living-room
Control station:
officeLaboratory
School storage
room
School library
Storage room

8

School library

910

Storage room
School storage
room
School classroom
Warehouse

2
3
4
5

11
12

Brick

-I

84

Brick

4

234

Brick

15

58

Brick
Brick

20
-1

22
21

Brick
Brick,
concrete
Brick,
stone
Brick
Brick

14
-2

25
31

12

24

1
7

25
18

Brick
Wood

5
0

18
17

Ta b l e

15

Activit concentrations in room air of rivate
anu lC Ul dm S 111 nns rue , ustr, a
Test
site
llo.

222Rn (Bq m- 3)

1
2
3
4
5
6
7
8
9
10
11
12

214 Pb ( Bq m-3)

Max.

Min.

t:,. 2_/
X

Max.

Min.

t:,. 2_!
X

276
174
61.1
34.0
82.9
74.0

26.3
<1.9
<1.9
<5.6
22.9
15.2
<5.6
16.7
<5.6
42.9
6.29
11.5

115
184
81.4 108115
31.5 32.6 49.6
37.4 29.6 30.7 52.2
13.7 13.0 13.3 27.4
21.8 45.1 46.3 73.3
24.8 42.6 43.3 57.0
72.9 45.9 50.0 81.8
17.4 41.4 42.2 29.6
53.3 35.5 37.0 46.6
20.4
57.4 58.1 71.4
36.3 27.0 27.8 45.1
24.8
32.6 33.7 54.0

26 .3
4.07
8.88
<1.9
21.5
9.25
2.22
12.2
2.22
28.1
5.55
2.96

71.4
26.6
30.0
17.8
25.5
21.1
59.2
6.66
25.2
30.0
34.0
30.0

124
61.1

82.5
80.7
45.9
58.8

Test
site
No.

MedianMean

220Rn (Bq m- 3)
Max.

Min.

t:,. 2_/X

Median<3.3
28.1
16. 3 <3.3
10.0
5.55
35.9 <3.3
74.0 23.3
32.6
<3.J
35.5
11.8
8.88 <3.3
33.7
7. 77

4

9

10
ll

12
a/

186

7.40
17.0
11.1
8.51
52.2 37.0
14.1
14.8
10.0 39 .2
17.8 10.4
16. 7 19.2
4.44 3.7
13.0 19.2

Mean

98. l
18.9
24.8
8.88
38.9
29.2
30.7
18.5
20.0
45.5

103
19.2
25.5
10. 7
40.0
30.0
38.1
19.6
20.7
46.3
25.9
22.9

24.4

21.1

212Pb (mBq m-3)t:,. 2_/
X

Mean

Max.

Min.

7 .77
8.51
40.7
18.5
41.4
11.1
20.7
3.7
20.7

5720
4110
6560
947
4590
3620
3300
4920
2780
3130
2600
507

1500 1420
755 2180
2230 2340
455
363
481 1910
1340 555
747 1520
2890 492
344 2080
1580 718
710 88159.2 259

1
2
3
5
6
7
8

MedianMedian Mean
3350
2000
4560
692
2450
1880
1860
3570
1890
2280
1670
285

is the largest observed increase of the activity concentration
within 24 hours.
t:,.

X

3470
2090
4700
703
2850
2180
1940
3600
1900
2320
1750
329

Tab l e

16

Correlation between radon and thoron concentration in houses
and meteorolo~ical variables[s 1)

Meteorological variable

Observation timeof meteorologicalchangeSign ofregression
coefficient

24 h
10 h

-1
-1

24 h

+l

24 h
24 h

+l

Change of barometric pressure
Change of barometric pressure
Change of soil temperature at
SO cm d£!pth
Change of daily mean temperaturein the open atmosphere
Change of daily mean wind speed
Temperature gradients between 574
and 918 m above sea level at 7 hChange of relative humidity
in the open atmosphere
Change of temperaturein the open atmosphere
Change of daily range of temperatLrein the open atmosphere-1+lTab 1e

7h

-1

7 h

+l

24 h

-1

17

Eguilibrium factors in dwellin9s in Finland 1977-1978[i;J20J

Type and numberof dwe 11 ings
Block of flats,
concrete (15)
Detached houses,
concrete (2}Block of flats,
brick (7}
Detached houses,
brick (5)
Detached houses,
wood (6)Radon conce~ 3ration(Bq m )
Max. Mean Min.

Equilibrium
factor
F

140

48

7.4

0.45

190

130

48

0.30

56

26

7.4

0.63

85

33

15

0.45

70

30

7.4

0.43

187

Tab le18

Dose equivalents per unit inhaledgotential alpha energy of 212 Pb and 212 8;.
assumin an AMA of 0.2-0.3 µm and a b1olo 1cal half-time of residence,n 1 ung forte transfer rom un~ toood 1n t e range of 0.2-0.5 ay

Dose equivalent per unit
inhaled poten!ial a-energy(Sv J )

Organ or tissue

Bronchial basal cells (8)Pulmonary region(P)[ Total lung average(Lu)Red bone marrow
Bone lining cells
KidneyLiver
SpleenOther tissues
Lung

Effective w8=wp:0,06
dose
equivalent wLu: 0.12
per unit
inhaled potentialalpha energy

3 - 5

9 - 101.2 - 2.5
1.5 - 35 - 5.5

0.25 - 0.15
3 - 2

O.Dl - 0.005

2 -0.4 - 0.25
0.08 - 0.05
0.03 - 0.02

0.9 -0.4
0.02 - 0.01
0.04 - 0.02
0.01 - 0.005

0.6(0.54 - 0.63)
0.5(0.47 - 0.54)

0.9(0.84 - 0.93)
0.7(0.66 - 0.70)p

Recommended effective dose equivalent
per unit inhaled potential alpha energy
for mixtures of 212 Pb and 212 si

Tab 1 e

4 - 5

0.7

19

Dosimetric coefficients relative to inhalationof radon daughters by miners

Quantity

Unit

Hefi 1pot

Sv/J\ff/C'pot
Heff/xeq

222Rndaughtersa/23
Sv/(J h m- )2.4
mSv/WLM
8.4..,sv/(Bq h m-3 ) 14

220Rn
daughters
E_/
0.7
0.84
2.9
64

~/ For inhalation of 222 Rn gas itself the effective
dose equivalent per unit activity inhaled isabout 1.5 10-lO Sv Bq- 1.
b/ The values refer to the inhalation of mixtures- of 212 Pb+ 212 Bi. For inhalation of 220 Rn+ 216 Po
the effective dose equivalent per unit inhalation
intake is about 1 10-lO Sv Bq-l.

188

Ta b l e

20

Breathing rates used for dose calculations{12]
Location

PeriodIndoors(19 h)

5.5 h
Bh
5.5 h

Outdoors
(5 h)

2 h
3 h

Breathing rate
20 l m)n_
7.5 l m!n-11
12. 5 l min. -1
20 l m~n_
12. 5 l m1n 1

Activity
light activity
restingi ntermcdi ate

Indoor total
Outdoor total
Grand total

21

T a b l e

Dosimetric coefficients relative to indoor
and outdoor inhalation of radon daughters by members of the public~/

Quantity

222 ~n daughters

220 Rn daughters~/

Indoors

Outdoors

Indoors

Outdoors

Sv/J
2.0
3.0
Sv/J h m- 3
1.6
3.0
5,5
mSv/WLM
11
1,1Sv/Bq h m· 3 8.7 10· 3 17 10· 3

0.7
0.55
1.9

0.7
0.7
2.5

40 10· 3

53 10· 3Unit

He ff/I pot
Heff/tpot
Heff~q~/ See Table 19 for the values relative to inhalation of 222 Rn and
220Rn+216Po.
b/ Inhalation of mixtures of 212 Pb+ 212 ai.

T a b 1 e

22

Annual effective dose e uivalents er unit of activit concentration,
or of potent1a a pa energy concentration,
for daughters of 227 Rn and of 220 Rn
and for outdoor and indoor exposure(Calculated with an annual breathing volume
3Vin ~ 5475 m3 indoors and Vout 1825 m outdoors)
InhaledContribution

Heff,cpot
Sv
J m-3

222Rn daughters
220Rn daughtersa/~/Indoors
Outdoors
Indoors
Outdoors

4

1.1 103
5.5 103
3.8 103
1.3 10Heff 1Xeq
rnsv
Bq m· 3

0.06!
0.031
0.29
0.10

Inhaled mixtures of 212 Pb and 212 Bi.

189

T a b l e 23
222 Rn and 212Pb concentrations in outdoor air
Mean value ( Bq rn
Location

222Rn

Ref.

212Pb

Austria
Bolivia
Finland

7.0
l. 5
2.3
3.5
3.8
2.0
2.7
3.6
France9.3
Germany, Fed.Rep. of 2.6
India
3.7
Japan
2.1
Peru
1.5
Philippines
0.3
Poland
3.3
Soviet Union
6.3
2.6
3.3
2.2
United Kingdom
3.3
United States (continental)
Chicago1.6
1.5
2.9
Washington
4.4
San Diego
0.1
San Francisco
0.6
Seattle0.1
Memphis
1.0
New York City
4.a
3.7
Chester. N.J.
7.9
Cincinnati
9.6
New Mexico
8.9
Puerto Rico
0.005
Alaska0.2
North Africa
0.5
Norwegian Sea
0.2
Pacific Islands
Hawaii0.2
0.05
Marshall Islands
0.02
Caroline Island
0.02
Mariannas (Guam)
0.05
Samoa
0.08
lndi an Ocean
0.07
North Atlantic
0.2South Pacific
0.07
Note:

1/ir
TM5
'MS
[MS
(MS)
fM5]
{MS]
fF4)
[ 16)
[R4)
[LBJ
[LBJ
'.86)
f P19)
[M2l

0.11
0.01
0.11
0.12
0.09

[Ml

[Ml)
fMl I
H6)

0.1
0.07
0.07

(86)
[86]
[B6]

0.007
0.002
0.004
0.7

'.86)
'86)
t86)
[86)
[GlO)
[13)
[FS)
[G12]
f~16]

fLB}

mi

0.001
0.001
0.008

[86)
[LS)

[L3)
[B6)
[B6)
[86)
(86)
(86)
(56]
(56]
[56)

0.004

The i>aZues given in this table should not
be considered to be mean values for theentire countries,

T a b l e

24

Nonnalized annual effective dose e uivalent from outdoor ex osure
20 % oft e tota time to ra on aug ters rom ra on re ease rom coalan geot enna pants an rorn ta, 1ngs

Normalized annual effective dose equivalentDistance(km)

Tailings

Geothennal
power plantArea a 104 m2
nSv(GW1e) a)-I µSv(GW(e) a)-I~~~~~~~µSv µSv(GW(e) a)-l

0.5

0.88

I
2
5

1.5
I. 3

10

190

Coal
power plant

0.57
0.31

5.5
9,4
7.9
3.4
1.8

2.7
1.1
0.3
0.08
0.03

11
4.3
0.08
0.3
0.1

Area

E

106 m2µSvµSv(GW(e) a)-l

21
14
8.8
4.6
2.4

0.9
0.6
0.4
0.2
0.09

Ta b 1e25

Radon concentration in waterRadon
concentrationin water

Number of we 11 s with radon
concentration in water
Location< 37

kBq m-J
Austria~urg
Finland
HeTsTrilZi and
Vantaa4
Other areas
11
I ta lY.
41
Sweden155
United States
Aroostock,Maine
13
Cumberland, Maine 1
Hancock. Maine
1
Lincoln, Maine
3
Penobscut, Maine
Waldo, Maine
York, Maine
All 7 counties
18
North Caro 1i na
84

37-370 0.37-3.7 3.7-37
kBq m-J MBr, m-3 MBq m- 3

llaximum Average1<.Bq m- 3 kBq m-3
7

12
34
16
17
19
6
3
6
10
5
6
55
117

65
30
2

7
11
10
6
9

29
7

9

52
10

4

Tab 1 e26'.S22]

150

1200
280
80
19

[CJ]
[CJ}
[113]
[Kl4]

200
5800
4600
1600
2400
3100
2200
5800
1700

48
1000
1400
560
540
1100
670
660
100

rHlO'
[HlO}
[HlO]
[HlO]
iHlO]
,HlO}
[HlO}
[HlO]
[Sl]

45000

2
1
1

1.5

Ref.

Distribution of radon concentration
1n dr1nk1ng water 1n F1nland(A7, All, C4, K18]

of
Water specification Number
persons(mi 11i on)
Waterworks
Dug wells
Drilled wells
Drilled wells
in Helsinki area
Weighted averageRadon concentration(kBq m- 3 )MeanMaximum

3.18

25

1.39

59

0.15

630

1600
1600
44000

0.02

1200
56

191

Ta b 1e27

Radon and radon daughter concentrations,n Canadian homes(H6]

Radon concentration(Bq 111- 3 )Equilibrium equivalentradon concentration(Bq m- 3 )Location

Ca 1gary, Alberta
Charlottetown,
Prince Edward Island
Fredericton, New Brunswick
Halifax, New BrunswickMontreal, Quebec
Quebec, QuebecSaint John, New Brunswick
Sherbrooke, Quebec
St. John's, Newfoundland
St. Lawrence, Newfoundland
Sudbury, On ta ri oThunder Bay, Ontario
Toronto, Ontario
Vancouver, British Colombia
Winnipeg, Manitoba
Brandon, Manitoba
Regina, Saskatchewan
Saskatoon, Saskatchewan
Edmonton, Alberta

Geometricmean

Geometric
standard
deviation

Geomctri cmeanGeometric
standard
deviation

II

3.6

7.0

2.3

15
24

5.3
4.0

6.7
12

II

3.3
3.8
5, 7'
5.4
4.4
6,8
4.0
4.5
2.8
3.0
4.1
4.8
3.6
4.3
4.6

2.6
2.9
3.1
2.5
2.7
3.0
3.3
2.7
4.6
3.0
2.6
2.6
2.0
3.4
2.7
3.1
3.3
3.3

II

10
10
13
11

33
21
20
11
5.2
51
30
47
16
16

Tab 1 e

5.2
4.8
6.7
8.5
5.6
6.3
13
9.3
6.7
3.3
26
16
19
16
16

28

Equilibrium equivalent radon concentration in houses
in Canada suspected of having enhanced concentrat,ons~K9]

Location

Port Hope (Radium/uranium refinery)
Cobourg (reference area) (Spring)(Autumn)
Uranium City (Uranium mining)
Elliot Lake (Uranium mining)
Bancroft area (Uranium mining)
Oeloro (Metallurgical operations)192

NL•mber ofhouses
2961
106
97
632
1921
1162
68

Average equilibrium
equivalentradon conc~~tration(Bq m )
11

5.2
5.6
48
30
26
22

Ta b1e29

Radon and radon dau hter concentrations in indoor air
an ra on concentrat1on 1n water supp y 1n ana a
[M7)
Ai r

Area

Location

Harrietsfield

Trailer
Trailer
Trailer
Trailer
Trailer
School: Washroom
Library
Big Acres
Basement
Sheldrake
Basement
Hubley Lake
Basement
KitchenFive Islands Boiler room
Lake
Trans fonner
WoodlandBasement
KitchenHighland Park Basement
Living room
West Timberlea Laundry roomRadon

EEC 2-_/(Bq m- 3 )(Bq m )

< lB.5

7.4
37
7.4
26
30
11

-3

118
< 22
< 74
152
93
< 18.5< 18.5
126
81
26
< 44
< 22
707
240
56
110
120

11

7.4
15
38
15
3.7
3.7
93
93
11

7.4
19

F ~/

Air-towater
concentration
Water
ratio
(MBq m- 3) ( 10- 4 )

> 0.4

.

5.8
6.1
5.6
5.8
6.2
5.5
5.5
5.5
4.7
1.6

0.3
> 0.3
> 0.3
0.2
0.1
> 0.6
> 0.4
0.1
0.5
> 0.6
> 0.1
> 0.2
0.1
0.4
> 0.2
0.1
0.2

< 0.030.2< 0.04
< 0.1

0.2
0.2
< 0.03< 0.03
0.1
0.5
< 0.2
< 0.1
< 0.1
0.5
0.2
0.08
0.2
0.1

3.6
14
7
12

a/ Equilibrium equivalent concentration of radon.
~/ Equilibrium factor.

Table

30

Radon and radon daughter concentrations in indoor air
due to warm water showers of 7 minutes
3
The :radon concentration in i.iate:r i.iaa 4. 4 kBq m- .

(M7~
Concentration
Bathroom

Before shower operation
During shower operationTimeelapsed(min)Dl

After shower operation

2
3
4
5
8
22
32
99

(Bq m- 3 )

Radon

Radon
daughters

19
148
850
1040
1890
2070
2740
3520
3100
2660
148

7.4

2400
110
26

Di stribut ion
ratio(10- 4)< 0.04

0.3
1.9
2.4
4.3
4.7
6.2
8.0

193

Tab l e

31

Radon concentration in air in Finnish dwell ins caused b radon in waterRadon concentration
Air (kBq m- 3)

Water
House
no.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Average

Rooms and situations wheremuch water is used (showers)

Rooms and situations where
little water is used (cooking)(MBq in- 3 )Room or situation number
4
1
2
3

Room or situation number
1
2
3
4
5

5.2
7.4
5.8
3.7
5.3
3.0
4.2
17
7.6
5.0
8.0
9.2
13
0.48
1.5
1.0
0.15
2.5
1.9
0.52
(5.1 ! 4.3)

4.2

4.0

0.81

2.1
3.9
15
2.6
39
6.0
23

22
2.1
9.2
2.5
29

1.2

1.5

5.8

0.93 0.59
1.6
4.6
6.7
0.67 0.85 9.3
0.19 b.41 0.41
5.9 27
0.81
4.7
3.4 1.4 6.0 3.0
6.8
0.3 1.0
0.74 1.8 0.26 0.30 2.9
3.3
8.7 134.2
0.89
0.037 0.037 0.11
0.15 0.56 2.6 o. 78
0.074
0.037 0.074
0.56 0.44

13
2.4

10

11

10
19
0.22
3,2
3.8
0.85
3.6

1.2

22
2.7
1.8
2 .1
0.67

8.5 ! 9.7

2.9 ! 4.7

Table

32

Equilibrium e9uivalent concentration of radon and thoron
1n dwell1ngs 1n the Federal Republic of Germany
Ranges <U'e given between p<U'entheses.
[W14]

Equilibrium equivale~tconcentration (Bq m- )Building material

Radon

ThoranConcrete based and mixedbuilding material
Sandstone10(3.7-25)
5.6

Brick

4.8
(3.7-6.3)
3.3(2.6-4.l}
3.7(3.0-4.8)

0.44(0.19-2.2)
0.30(0.11-0.48)
0. 70(0.30-1.1)
0.11

Aerated concreteLight-weightbuilding material
Weighted average

8.1(2.6-25)

Table

0.19
(0.11-0.26)
0.37(0.11-2.2)

33

Radon concentration in dwellings
1n Norwat 1977-1978

t 24J

Type ofdwe 11 i ng
Wood
Concrete
Brick

194

Radon concentration(Bq m- 3)
Min.

Mean

Max.

7.4
7.4
11

48
74
37

140
250
210

Living rooms(no water)

0.34
0.53
0.093
0.23
0.30
0.23
0.13
0. 36
0.31
0.31
0.20
0.13
0.77
0.019
0.059
0.041
0.037
0.11
0.056
0.078
0.22 ! 0.19

Ta b l e

34

Radon and radon dau hter concentrations in flats in Poland

Location andbuilding material

Maximum
concentrationof radonNo. offlats(Bq m- 3 )Warsaw
ll17f'e're nt types ofconcrete
LublinConcrete and gypsum
Concrete, siporex
and gypsum
Wood
Brick
Limestone
Clay
Clay and brick
Slag and cement
Clay, slag and cement
Brick and siporex
Concrete and siporex
Brick, slag and cement

Equilibrium
equivalent radon
concentration(Bq m- 3 )Range

Weighted
averageII

2.2-281.1-14

7.0

39

15

0.4-7.8

2.0

32
9
29
3
6
4
12
2
5
7
10

23
2.1-9.4
I. 2-33
2.4-192.3-17
1.6-17
4.4-52
9. 3-16
2.3-14
1.5-7.4
2.9-280.4-13
1.0-4.8
0.63-17
1.2-8.9
1.2-8.5
0.81-8.5
2.3-27
4.8-8.5
1.2-7.8
0.78-4.!
I. 3-14

3.7
2.9
8.9
4.8
4.8
4.8
15
6.7
4.4
2.4
7.8

Weighted average of all flats

T a b l e

5.6

35
rates
e a

Concentration
Date
ready Number offorhousesmoving
in
1969

9

1962

7

1968

9

1967

7

Building
material

Radon(Bq m- 3)

Entirely780
built of (535-1160)
alum shale
aerated concrete490
All walls
built of (320-690)
alum shale
aerated concrete370
as above( 190-490)
As above590(175-820)

Radon
daughters(Bq m- 3 )Absorbed
dose rate inAir
air from
exchange gammarat~ 1
radiatiQ~(nGy h )(h )410( 190-770)0.31(0.21-0.43)635(580-690)

185(80-250)

0.41(D.24-0.55)

380(350-440)170(75-280)245( 45-355)

0.49(0.34-0.61)
0.27(0.17-0.49)425(410-440)540(480-600)

a/ The lowest and highest values calculated as averages for a house are given
in parentheses.

195

Table36

The concentrations of radon and dau hter roducts
1n
e 1ngs 1n a we 1s own

[£2]

Air
exchange
rate
(h-1)

Building materials
in the walls
and ventilation systemRadon(!lq 111-3)
II!I

Multi-farnil! houses
Concrete, M

0.3-0.6

Concrete and sandbased
aerated concrete, ME

0.5-0.9

Concrete and sandbased andalum shale based aerated
concrete, ME
Sin le-famil houses
aca e rick san stone),wood construction, ME

0.4-0.8

Wood, cellar of alum shalebased aerated concrete, ME

0.4-0. 7

0.4-0.7

Wood, no cellar, ME

0.8

Alum shale based aerated
concrete, DV

0.2-0.5

Facade brick (clay), woodconstruction, DV

0.1-0.2

lowaveragehighlowaveragehigh•lowaverage
high

59
170
590
37
89
150
74
180
440

48
140
780
26
85
140
93
160
410

d/
5'6'
140
n d/
20ll"
370
100
100
100
150
270
410
220
410
560

low
averagehighlowaveragehighlowaveragehighlowaveragehighlowaveragehigh11Equilibrium
equivalentradon concentration(Bq m- 3) ~/
II

c/

22 11
70 52
260 310
9
13
31 23
48 41
22 11
52 44
150 140
8
22
38
4
81
140
33
37
41
67
120
190
82
170
310

a/ ME is a mechanical exhaust ventilation system, DV is a draught ventilation system in the houses studied with a fan over the cooker.
b/ The radon daughter concentrations were measured
c/ I and II mean the first and second phases between which the ventilation
systems were adjusted_
d/ n ~ minimum detectable value, 26 Bq m 3 for radon.

37

Ta b l E

Average radon concentrations
1n Swe~1sh dwellings~S35]

Radon concentration (Bq mHouses
existing
inApartmenthousesDetached
housesAverage1950
1975
1985 a/

43
89

18
48
51

29
71
73

as

a/ Predic :ed values.

196

Tatle38

Equilibrium e~uivalent radon concentrations in houses
built on p osphate land in the United States{08)

Structure

Slab-ongrade

Crawl spaceand mobile
homes
2_/

Equilibrium equivalent concentration!
(Bq m- 3 )Type of land

Geometric mean

Range

11

3.7-3770
30
30

11-170
7-140
15-67

160
11
22

70-5203.7-37
3.7-52

Undisturbed
Unmined, near-surface
radioactive deposits and fill
Tailings
Lower activity overburdenlligher activity
overburden and debris
Undisturbed
Reclaimed

The weighted average was 37 Bq m- 3, which is estimated to be 26 Bq mabove normal background.

Tatle

3

39

Equilibrium equivalent radon concentrations
in houses 1n Colorado, United States
11

Number ofhousesEquilibrium equivalentconcentr~tion(Bq m )

15
26

> 196
52-19619- 48< 19

5

1

Tab l eE uilibrium e

40

concentrations of radon and annual effective dose e uivalents
The equitibri:,m factor is assu:ned to be 0.5.

Country
or area

Structure

Austria
CanadaDenmark
FinlandGermany,Fed.Rep.
Hungary

Average for Salzburg
Typical Canadian homes
Basement room, thick structured elements
Flats other than groundfloor
Average for 32 houses
Isolated rooms
As specified in Table 28, Annex 8 fU6)
Flats other than groundfloor
Average value
Average value

NorwayPolandSwedenUnited Kingdom

Average va 1ue
Single-family houses
Average value
United States
New Jersey and New York andas specified in Table 28, Annex B [U6]
USSR
Flats other than groundfloor
Single-family houses and groundfloor flats
Several countries Mainly masonry houses and apartments

Equilibrium
equivalentconcentration(Bq m- 3)

Annualeffective dose
equivalent
(mSv)

Ref.

12
17
4.8
17
8.1
20
120
11
26
6-17

0.7
1.0
0.3
1.0
0.5
1.2
7.3
0.7
1.6
0.4-1.0

60
15
13

3.7
0.9
0.8

[NZ]
[U6)
[NZ]
[S24]
(Gl3,B16,
B17, U6)
[Rl5]
IN2)
C6)

15
4.8
16
18

0.9
0.3
1.0
1.1

[U6]
[NZ]
[NZ]
(U6]

[SZ2)
'M6)
tN2]
!NZ]
Wl4]

197

Ta b l e
Radon and thoron

41
1ng omEquilibrium equivalentconcentration (Bq m- 3 )RadonThoron

14
0.7
41
13
54
91
89
6.4

0.33
0.08
1.2
0.12
0.33
0.41
0.44
0.43

Ta b l e

in different rooms

Radon-to-thoron
equilibrium
equivalentconcentration
ratio
42
9

34
110
160
220
200
15

42

Concentrations of, and exeos ure to, radon daughters in uranium mines

Country

Year

France

1971
1972
1973
1974
1975
1976
1977
1978
1979
1975
1976
1977
1975
1978

United States
Italy
Canada1 Leaching
4 Undergroundl Open pit

1978
1979
Argentina
Underground 1977-79
1980
Open pit
1980

Average annua I
Averagepotenti a 1 alpha No. of
potentialalpha energy energy exposure minersconcentration
(WLM)
(WL)
0.18
0.17
0.18
0.13
0.11

[U6]

2.0
0.71
0.58
0.51
< 1

1.4
5.68
4.64
4.08

o. 38

1284
1503
- 5000- 5000- 5000

- 140
51

fB7)
B20]
[R6]
[54]
[A6]

0.74
0.41
0.72
0. 74

630
3690
276
4535
6883

9
l

2.4
2.4
0.12

286-379
95
285

0
0

a/ The maximum permissible exposure in many countries.
fi/ Data from the tla ti ona 1 Dose Regis try in Canada.

198

No. ofRef.
minersexceeding
4 WLM ~/

b/

(Pl8]

T a b 1e

43

Est ima te_cl_Jioten t i al alpha energy exprureof different cate~ories of mine wor ers
in the Jaduguda un erground mines, India(Rl3, Kl9, Al2)

Estimated potential alphaenergy exposure {WLM)
Year
Dri 11 i ng crew

Mucking crew

Others4,9 ± 2.6
2.3 ± 1.2
2 .0 ± 1.1
3.8 ± 2.0
4.1 ± 2.2
2.1 ± 1.1
1.7 :1: 0.9
o. 7 :1: 0.6
0.6 ± 0.3
1.6 t 0.6
2.2 t 0.7
5.5 ± 4.4
1.6 ± 0.6
0.8 :t 0.2
2.6 t 1.0

2.1 ± 1.0
3.5 ± 1.8
5.2 ± 2.7
3.2 ± 1.6
6.5 ± 3.4
3.0 ± 1.4
2.0±1.l
1.6 t 1.4
0,6 ± 0.3
5.5±5,0•
2.3 t 1.9
2.5 ± 1.1
1.7 :1: 0.7
1.4 ± 0.7
2.1 t 0.6

1.7 ± 1.0
1.2 ± 0.9
1.6 ± 1.1
2.3 ± 1.5
2.4 ± 1.7
0.7 ± 0.5
1.1 ± 0.8
1.4 t 1.3
0. 7 :1: 0.5
2.0 :1: 1.6
3.5 ± 1.7
0.7 t 0.1
1.4 ± 0.7

1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979

T a b l e

1.7 ± 0.3

44

Concentrations of, and exeosure to, radon daughters in non-uranium mines!/

Country

Finland
Italy
NorwayYear

1972-1974
1975-1977
1975
1972
1980
1970

PolandCopperIron
PyritePhosphate
Zinc and 1ead
BaryteCoal
South Africa
1973
Sweden
1970
1974
1975
1976
1977
1978
1979
1980
United Kingdom 19681976
National coal 1981
Private coal
1981
Other than
coal
1981
United States
1975
1976
1977

Averagepotentialalpha energy
concentration{WL)

Annual potentialalpha energy
exposure(WLM)

0.2-0.4
0.38
0.01-0.6
0.07
0.05

0.64
0.45

1-2
1
4
0.8
0.9
0.2
0.1
1. 7
4.8
2.1
1.9
1. 7
1.6
0.9
0.7
0.7
0.01 ~/

2-3 c/
o.T2
0.24
2.60

0.31
0.22
0.12

No. ofNo. ofminersminers Ref.
/mines exceeding
4 WLM
1300/23[AS]
1370/160
2500/16 - 75
[S4]
1870/33[S54,S55]
1380/23[D3]3200004800/5 2000
4600/50 360
5300/45 270
5300/46 225
5200/45 475
5300/47 270
4400/3504400/35
0220000/420
2000/80 560
185200
1500

[U6]
[U6]
[U6]
[S13]
[U6]
[Sl3]
[S13]

94

[08]
[R6]

2346/108

[El]

[S56]
[04)
f04]
[08]
[08]

/163

If not otherwise noted, the mines <re iron. zinc, lead, copper or gold mines.
In reference [04], this value is c~lled "typical" for large nationalized
coal mines.
~/ Based on measurements in about 80 i of all non-coal mines.
a/

o/

199

Tab 1 e

45

Concentration of and ex osure to, radon dau hters
1n wor ng paces ot er tan m nes
Country
Kind of roomor working
place

Annua 1 potential
Averagepotential alpha alpha energy
exposure
energyconcentration
(WLM)
(WL)

Number ofworkers/
working
placesRef.

Austrial'ulilTcba ths(Badgastein)

0. 5-0. 9

6-11

p_/

/>100

[P7)

~
caves

0.45 !I

5

£_/

/3

(R9)

~
0 pas

0.001

0.02-24(18 spas < I WLM)

/20

[S5)

~
caves

0.8 !I[M23)

SwedenTunnels for water
Tunnels for cables
Defence installations
Hydro-electric
power stations- 0.1-1

1.1
0.45
1 - 4 5_/

United States
6 caves

0.1 - 1.5

0.3 - I

11 /1
34/2

[S!3j
[S13
(S13)

200/78[S!3]/6(Yl,S46)a/ An equilibrium factor F of 0.5 is assumed.
An annual occupancy of 2000 his assumed.
c/ For about 3 % of the staff.

Fi/ A fictitious value.

Table 46
Measured va 1ues of the concentrations of 220Rn, 212 Pb and 212 0; at a as mantle factor

Time ofmeasurement{h)Location

212Pb
concentrations(Bq m- 3 )First day
10.50 Impregnating room
270
Impregnating room
11.20
150
12 .10 Drying room140
12.20 Drying room130
12.40 Drying room140
12.50 Drying room
110
Impregnating room
15.25
220
15.40 Impregnating room
290
Second day
11.00 Impregnating room270
I 1.25 Thorium nitrate store 100
11.40 Thorium nitrate store 70
12.00 Drying room130
12 .15 Drying room
200
2-_/

212 8iconcentrations(Bq m- 3 )Ventil220Rn
220Rn
Ratios ofation rate Inferred
Measured
220R i fd the measured
in roomn n erre concentrations
concentration concentration·air {h - I)
220 Rn measure6 20 Rn: 212 Pb: 212 si(Bq m- 3)(Bq m- 3 )
a/

35
23
21
21
19
13
28
31

63
140
140
33
160
210
170
210

7400
8900
8500
7400
9300
10000
16000
26000

22000
13000
6300
5900
4800
5200
!8000
26000

0.3
0.7
1.4
1.2
1.9
1.9
0.9
1.0

100: 1.2 :0. 75
100:1.1 :0.18
100:2.2:0.33
100:2.3:0.li
100:2.8:0.38
100:2.2:0.24
100:1.2:0.16
100:1.1 :0.12

48
48
22
26
29

120
30
56
100
150

14000
1500
1700
5900
13000

!6000
3700
2000
3000
5600

0.8
0.4
0.8
2.0
2.3

1001.70.19
100 2.8 1.3
100 3.5 1.1
100 4.5 0.89
100 3.6 0.53

Inferred from the 212 Pb and 212 Bi concentrations.

200

Table47

Typical variations of the potential alpha energy
concentration of thoron dau hters at different locations
1n at orium actor in
I 4

Location

WL

Evaporator room
Area around mother liquor tank
Fi 11 i ng room
Crushing room
Area a round hydroxide tanks
Drying room
Area around chloride filter presses
Laboratory
Area around tanks

Tab l e

0.04
0.12
0.13
0.40
0.06
0.24
0.10
0.16
0.07

48

Increase in collective effective dose equivalents caused byradon dau~hters per unit of electrical energy
conservedy reduction of the vent1lat1on rate-1
(to a rate not less than 0.5 h l for Swedish houses built up to 1970

Type of houseand building material

Normalized collective effective dose equivalent(10 3 man Sv (GW(e) a)- 1 )Wooden house
Wooden house, cellar walls ofconcrete based on alum shale
Brick/concrete
Sand based aerated concrete
Concrete based on alum shale
Weighted average

Multi-family
houses2.8

Single-family
houses

Weighted
average

1.4
11

11

1.8

20

5.7
2.9
7.5

14

8.7

2.2

5.6

8.4

7.0
2.9

201

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