NATION WIDE 222Rn AND 220Rn ATLAS FOR INDIA
T.V. Ramachandan1, L.A. Sathish2* and S. Sundareshan3
1

Ex-Environmental Assessment Division, Bhabha Atomic Research Center, Mumbai- 450
085, India
2
Department of Physics, Government Science College, Bangalore – 560 001, India
3
Department of Physics, Vijaya College, Bangalore – 560 004, India
*Corresponding Author (Sathish) Email: lasgayit@yahoo.com

Abstract
Considering the epidemiological effect of radon on human beings, an attempt is made to
make a nation-wide atlas of

222

Rn and

220

Rn for India. More than 5000 measurements have

been carried out in 1500 dwellings across the country, India. The solid state nuclear track
detectors were deployed for the measurement of indoor 222Rn, 220Rn and their progeny levels.
The mean annual inhalation dose rate due to 222Rn,

220

Rn and their progeny in the dwellings

is found to be 0.97 mSv y1 (GSD 2.49). It is observed that the major contribution to the
indoor inhalation dose is due to 222Rn and its progeny. However, the contribution due to 220Rn
and its progeny is not trivial as it is about 20% of the total indoor inhalation dose rates. The
dependence of indoor

222

Rn levels in dwellings has shown a significant difference between

the nature of walls and floorings. The results are discussed in detail.
Key words: 222Rn, 220Rn, inhalation, radiation doses.
Corresponding Author:
Dr.Sathish.L.A
Assistant Professor
Department of Physics
Government Science College
Nrupathunga Road,
Bangalore – 560 001
India
+91-80-9886639324

1

Introduction
Ever since studies on uranium miners established the presence of a positive risk coefficient
222

for the occurrence of lung cancer in miners exposed to elevated levels of

Rn and its

progeny, there has been a great upsurge of interest in programmes concerned with the
measurement of radon in the environment. This interest was accentuated by the observations
of elevated radon levels in the indoor environment in many countries that led to the
realization of residential radon as being a possible public health issue in the western world. It
was also hoped that in conjunction with epidemiological studies, large-scale indoor
surveys might lead to quantitative understanding of the low dose effects of

222

222

Rn

Rn exposures.

As a result of these, considerable amount of information is available on the levels of

222

Rn

gas and its progeny in the indoor environment across the globe (UNSCEAR, 2000). In
contrast, there exist a few studies relating to the measurements of

220

Rn in the environment

(Doi and Kobayashi 1994; Doi et al, 1994) since it is assumed that the inhalation dose to the
general population from 220Rn and its progeny is only about 10% of the inhalation dose due to
222

Rn (UNSCEAR, 2000). But, recent studies in many countries have revealed that this

assumption if far from the truth (Steinhausler et al, 1994). In general, such studies are
important in two ways. Firstly, any radiological impact assessment of nuclear facilities, either
existing or those to be set up in the future, requires information on the exposure due to natural
radiation prevalent in their vicinity. Secondly, the radiation risk coefficients are fairly well
established at high doses and high dose rates, whereas little is known about the effects of
radiation at low dose rates. Several epidemiological study programmes in different countries
are in progress to estimate the population exposures due to natural radiation with a view to
obtain the radiation risk coefficients at low dose rate levels. In this regard, radiation surveys
in high background areas will provide an excellent setting for epidemiological studies relating
to the effects of low doses of radiation. In view of these, a comprehensive estimate of the
natural inhalation dose requires both

222

Rn and

220

Rn levels in the indoor and outdoor

atmosphere.

Sources of 222Rn and 220Rn
Radionuclides such as 222Rn and 220Rn, from the uranium and thorium decay chains are noble
gases produced by the decay of their immediate respective parent nuclides,

226

Ra and

224

Ra,

present in natural rocks, uranium ores and soils (Fleischer, 1997). The decay products of
222

Rn and

220

Rn are the radioactive isotopes of polonium, bismuth, lead and thallium.

decay products are divided into two groups; the short-lived

222

Rn daughters such as

222

Rn

218

Po
2

(RaA),
222

214

Pb (RaB),

214

214

Po (RaC1) with half-lives below 30 min, and long-lived

Bi (RaC),
210

Rn decay products such as

Pb (RaD), Bi (RaE),

210

Po (RaF). However,

220

Rn progeny

has no long-lived group. Most important radionuclide in this chain is the lead isotope

212

Pb

with a half-life of 10.6 h. These daughter products, being the isotopes of heavy metals, get
attached to the existing aerosols, suspended particulate matters, in the atmosphere. Their
elimination from the atmosphere occurs either by radioactive decay or by other removal
processes such as plate-out or surface deposition and washout by rain. Vast differences in the
half-lives of

222

Rn (3.8 d) and

220

Rn (55 s) is a crucial parameter in governing their release

from the ground and subsequent distribution in the free atmosphere. When radium decays in
soil grains, the resulting atoms of
filled pores. The fraction of

222

222

Rn isotopes first escape from the mineral grains to air-

Rn escapes into the pores is known as the emanation power

fraction. Even though the detailed processes responsible for

222

Rn emanation from grains are

not fully understood, it is believed that the main contribution to the emanation comes from
the recoil processes (Nazaroff, 1988). The recoil range is about 0.04 - 0.06 µm in grain
materials and about 60 µm in air (Tanner, 1980). Also, recoil-stopping distance of
220

222

Rn and

Rn is lower in water than in air. Hence, the moisture content influences the emanation

power fraction (Megumi and Mamuro, 1974; Strong and Levins, 1982; Ingersall, 1983;
Stranden et al, 1984). Emanation power fraction of building materials for 220Rn is about 2-10
times smaller than that for

222

Rn, despite the greater recoil energy of

220

Rn atoms

(Porstendorfer, 1994). Experimental studies on building show that it ranges from 0.2 to 30%
for
222

222

Rn and 0.2 to 6% for

220

Rn (Porstendorfer, 1994; Barretto et al, 1972). Transport of

Rn through the soil takes place by diffusion and/or with gases like CO2 and CH4 or water

moving in the soil horizons. The diffusion coefficient for

222

Rn in different soil types varies

from 10-9 to 10-5 m2 s-1 from water to air media (UNSCEAR, 1992). 222Rn and 220Rn enter the
atmosphere mainly by crossing the soil-air or building material-air interface. Typical values
of exhalation rate (amount of activity released per unit area of the surface per unit time) for
222

Rn in soil and building material are 0.02 and 5.0 × 10-4 Bqm2s-1, respectively. The same for

220

Rn are as high as 1 and 0.05 Bqm-2sl, respectively (Porstendorfer, 1994).

222

Rn and

220

Rn

progeny aerosols in the atmosphere are generated in two steps. After the formation from the
222

Rn isotope by decay, the freshly generated radionuclides react very fast with trace gases

and air vapors, and become small particles, called clusters or unattached radionuclides with
diameters varying from 0.5 to 5 nm. In addition, these radionuclides attach to the existing
aerosol particles in the atmosphere within 1 - 100s, forming the radioactive aerosols. Most of
the newly formed decay product clusters are positively charged and have a high mobility
3

(Porstendorfer and Mercer, 1979). Mobility is characterized by the diffusion coefficient that
mainly controls the formation of the radioactive aerosol by attachment and their deposition
on surfaces and in the human lung.
222

Rn and

220

Rn in indoor environments mainly originate from emanation of the gases from

the walls, floor and ceilings. Most terrestrial building materials have 3-4 orders of magnitude
higher gas concentrations in pore spaces than in the atmosphere, permanently maintained by
the continuous decay of its parent nuclides. High concentration leads to a large
gradient between the materials and open air. Levels of

222

Rn and

220

222

Rn /220Rn

Rn in the open

atmosphere are governed by the balance between the exhalation rate and the atmospheric
dilution processes.
The external gamma dose rates have been more or less well mapped in India by several
studies. A countrywide survey of outdoor natural gamma radiation levels using Thermo
Luminescent Dosimeters (TLD) covering quite large number of locations scattered all over
the country revealed that the average external gamma radiation dose for the country is about
775 µGy yr-1 (Nambi et al, 1986). Mishra and Sadasivan (1971) have projected a national
average value of 707 µGy yr-1 based on natural radioactivity analysis of undisturbed soil
samples from more than 30 different locations, all over the country, assuming a uniform
cosmic ray component of 287 µGy yr-1. Of the terrestrial component, 48.7% of the
contribution is from

40

K and the remainder is by the thorium (33.6%) and uranium series

(17.7%) (Sadasivan et al, 2003). Tables 1 and 2 give the estimated natural radioactivity
content in the building materials used for construction in India and the distribution of
and

232

Th in Indian soil (Sadasivan et al, 2003). It can be seen from these tables that

238

40

U

K is

also a major source of radiation in the environment. A good database on the countrywide
concentration levels of

238

U,

232

Th and

40

K in geological materials as shown in Table 3

(Sankaran et al, 1986). Table 4 gives the estimated ranges of

222

Rn entry rate from different

sources in typical houses (ICRP, 1986). It is evident that soil has the highest entry rates
followed by brick or concrete.
Environmental measurements of
earlier. Since 1970, indoor

222

222

Rn were mostly confined to outdoor atmospheric air

Rn levels were measured with keen interest, and several large-

scale surveys have been carried out by several agencies all over the world (Campos-Venuti et
al, 1994; UNSCEAR, 2000). Typical worldwide indoor and outdoor levels of 222Rn are about
45 and 7 Bq m-3, respectively and that of outdoor

220

Rn level is estimated as 0.2 Bq m-3

4

(Mettler and Upton, 1995). An initial survey in Indian houses indicates that the indoor

222

Rn

concentration varied between 2.2 to 56 Bq m-3 with a geometric mean of 15.1 Bq m-3 (Subba
Ramu et al, 1993). The reported indoor 222Rn and 220Rn levels are tabulated in Tables 5 and 6
respectively, shows that the population weighted worldwide average

222

Rn concentration is

39 Bq m-3; while the geometric mean calculated for the data is 30 Bq m-3 with a geometric
standard deviation of 2.3 (UNSCEAR, 2000). Average equilibrium equivalent concentration
of

220

Rn (Table 6) range between 0.2 and 12 Bq m-3, while the ratio of

222

Rn/220Rn EEC

varied from 0 . 0 1 to 0.5 worldwide. All this information facilitated the understanding of
many environmental processes, which affect the distribution of

222

Rn and

220

Rn levels in

indoors and outdoors and the related radiation exposure to man. However, there exist still
many problems associated with the accurate assessment of exposures and radiation doses to
general population due to 222Rn, 220Rn and their progeny.

Measurement Methodology
The present national survey covered 25 locations. About 1500 houses of different types of
construction were surveyed on a time integrated quarterly cycle of 90 days covering all the
four seasons of a calendar year. Solid State Nuclear Track Detector (SSNTD) based
dosimeters (Nikolaeve and Ilic, 1999; Subba Ramu et al, 1994) were used for the survey.
These are simple to use and less expensive as compared to some continuous measurement
systems like the AlphaGuard. The latter is useful for occasional comparisons with the
SSNTD based dosimeters. In view of this, SSNTD based dosimeters, described in the
following section, were developed and calibrated for the national survey. Since the sampling
is passive and integrated for long duration, the diurnal and seasonal variations in radon
concentrations are being taken into account (Ilic and Suteg, 1997).
SSNTD based dosimeter System developed is a cylindrical plastic chamber divided into two
equal compartments (Nambi et al, 1994), each having an inner volume of 135 cm3 and height
4.5 cm. Dimensions of the dosimeter are chosen based on the ratio of the effective volume of
the cup to its total volume to achieve maximum track registration for the cylindrical cup (Jha
et al, 1982). The design of the dosimeter is well suited to discriminate

222

Rn and

220

Rn in

mixed field situations, where both the gases are present as in the monazite deposited areas.
Cellulose nitrate films of LR-115 type II manufactured by the Kodak Pathe are used as
detectors. The 12 µm thick film cut into 2.5 cm × 2.5 cm size is affixed at the bottom of each
cup as well as on the outer surface of the dosimeter. The exposure of the detector inside the

5

cup is termed as cup mode and the one exposed open is termed as the bare mode. One of the
cups has its entry covered with a glass fiber filter paper that permeates both 222Rn and 220Rn
gases into the cup and is called the filter cup. The other cup is covered with a semi-permeable
membrane (Ward et al, 1977) sandwiched between two-glass fiber filter papers and is called
the membrane cup. This membrane has permeability constant in the range of 10-8 -10-7 cm2s-1
(Wafaa, 2002) and allow more than 95 % of the
entry of

220

Rn and

Rn gas to diffuse while it suppress the

Rn gas almost completely. Thus, the SSNTD film inside the membrane cup

registers tracks contributed by
222

222

220

222

Rn only, while that in the filter cup records tracks due to

Rn. The third SSNTD film exposed in the bare mode registers alpha tracks

contributed by the concentrations of both the gases and their alpha emitting progeny.
The dosimeter is kept at a height of 1.5 m from the ground and care is taken to keep the bare
card at least 10 cm away from any surface. This ensures that errors due to tracks from
deposited activity from nearby surfaces are avoided, since the ranges of alpha particles from
222

Rn /220Rn progeny fall within 10 cm distance. After the exposure period of 90 days, the

SSNTD films are retrieved and chemically etched in 2.5 N NaOH solutions at 60 °C for 60
minutes with mild agitation throughout (Miles, 1997). The tracks recorded in all the three
SSNTD films are counted using a spark counter. A methodology has been developed to
derive the equilibrium factors separately for

222

Rn and

220

Rn using the track densities based

on the ventilation rates in the dwellings (Mayya et al, 1998).One may expect deposition of
activity on the SSNTD film in the bare mode exposure, which may pose as an unknown
parameter in the calibration factor. But it has been proved that the LR-115 (12 µm) film does
not register tracks from deposited activity (Eappen et al, 2004). This is because the Emax for
LR-115 film is 4 MeV and all the progeny isotopes of 222Rn /220Rn emit alphas with energies
greater than 5 MeV.

Calibration Facility and Standardization of Dosimeter
Experiments were carried out at the Bhabha Atomic Research Centre, Mumbai, India to
estimate the calibration factors (Ramachandran et al, 1995) separately for 222Rn and 220Rn, in
a calibration chamber of stainless steel of 0.5 m3 volume.

222

Rn (or

220

Rn) gas is introduced

into the chamber from standard sources obtained from Pylon, Canada. The calibration
chamber has provisions for imputing aerosols from an aerosol generator, which is a Sinclair
LaMer type condensation aerosol generator. It gives a laminar flow of mono-dispersed
aerosols of di-2-ethylhexyl sebacate condensed on NaCl nuclei. The temperature settings of
the boiler and re-heater are adjusted to obtain mono-dispersed aerosols of 0.25 µm diameter,

6

which is close to the activity median aerodynamic diameter of 0.2 |µm reported for indoor
aerosols (Yihe et al, 1996). Aerosol concentrations of the order of 104 to I05 particles per cm3
of air were generated to simulate the indoor environment conditions. Depletion of the
aerosols inside the chamber was studied and accordingly input of the aerosols was regulated
to maintain a near constant particle concentrations. The chamber has provisions for coupling
an on-line Lucas cell system in conjunction with an AlphaGuard for continuous measurement
of

222

Rn gas concentration. The AlphaGuard, kept inside the chamber recorded hourly

averaged

222

Rn concentrations. The on-line Lucas cell system was coupled to an alpha

counting setup and counts were taken synchronizing with the timing of the AlphaGuard.
The comparison of

222

Rn measured by the two systems for a wide range of concentrations

showed very good correlation of regression coefficient 0.97 and has a slope equal to unity
(Eappen et al, 2001). Calibration factors (concentration conversion factors) for

222

Rn and

220

Rn are required to convert the recorded tracks in the exposed SSNTD films into 222Rn and

220

Rn concentrations. Calibration factors were estimated experimentally as well as

theoretically for all the three modes of exposures. These are discussed in the following
sections.
Calibration factors (CFs) for 222Rn and 220Rn gases in the cup mode were determined through
a series of experiments. CFs for 222Rn (kR) and for 220Rn (kT) in terms of tr cm-2 per Bq d m-3
can be obtained as:

kR =

24T
CR H

and

kT =

24T
CT H

where, T is the tracks per unit area (tr cm-2), CR is concentration of the
CT is the level of

220

222

Rn gas (Bq m-3),

Rn gas (Bq m-3) and H is the exposure time (hours). Experimentally

obtained calibration factors for 222Rn and 220Rn are given in Table 7 for cup mode exposure.
CF for 222Rn in the membrane compartment is found to be equal (0.019 tr cm-2 / Bq d m-3) to
that in filter paper compartment (0.02 tr cm-2/Bq d m-3). CF for 220Rn in the membrane cup is
essentially zero and that in the filter paper cup is 0.017 tr cm-2/Bq d m-3. The definition of
the CF for the bare mode has certain ambiguities. In the earlier approach, the CF for the bare
detector was defined as the track density rate obtained per unit WL (Barillion and
Chambraudet, 2000; Durrani and Ilic, 1997). In reality, track formation rate in the bare mode
is not a unique function of WL, but would depend on the equilibrium factor (F). If one
defines the bare detector calibration factor as kB (tr cm-2/Bq d m-3) of each species, it may be
easy to show that this quantity is independent of the equilibrium factor as well as the

7

incident energy of the alpha particle. For a given track density rate 7(tr cm-2 d-1) and working
level (WR for

222

Rn and WT for

220

Rn in mWL units) and the corresponding equilibrium

factors, FR and FT, the calibration factors as defined above can be obtained for
and

220

-2

222

Rn (kBR)

-3

Rn (kBT) respectively in terms of tr cm / Bq d m using the following equations.

! T "! FR "
k BR = #
$#
$
% 3.7WR &% 1+2FR &
T
!
"! FT "
k BT = #
$#
$
% 0.275Wr &% 2 + Fr &
Based on this concept CFs was derived for the species matrix for

222

Rn,

220

Rn and their

progeny concentrations. They were found to be nearly constant for a wide range of
equilibrium factors (0.1 - 0.72) supporting the basic assumption of the new approach. Table 7
shows the results of the CFs for the bare mode exposure for
222

222

Rn and

220

Rn. The CF for

Rn and 220Rn are estimated as 0.02 tr cm-2/Bq d m-3and 0.019 tr cm-2/Bq d m-3, respectively

and are nearly identical. This confirms the assumption that the bare card calibration factors
are the same for the alpha emitters since they are functions of only the difference in the
ranges and the lower and upper cut off energies of the detector. Hence for practical use, an
average value of 0.02 tr cm-2/Bq d m-3may be used as the CF for

222

Rn and 220Rn in the bare

mode exposure. A Theoretical model has been developed to derive the calibration factors for
222

Rn and 220Rn for all the exposure modes (Eappen and Mayya, 2004). The theoretical model

is based on certain parametric constants chosen after experimental verifications. These
include the bulk-etching rate and the break down thickness for the spark counting technique.
The present calculation uses bulk etching rate as 4.0 µm/h and break down thickness as 3.0
µm. In the model, the upper and lower cut off energies for normal incident alphas are
translated as residual ranges using the range energy relationship. The sphere of influence for
the upper and lower cut off energies from normal incident angle to critical angle can be
obtained from integrating for the total area covered under solid angle for residual length of
alpha particles lying within those incident angles. With these considerations, the observable
tracks per unit area on the film per unit exposure time can be computed using the following
equation.
2$

#

R "R

c
F
U
&c
Tr =
d
%
d
#
sin
# cos#dr
4$ !0 # != 0 r = RE "!RL (# )

8

where η is the efficiency of track registration, C is the activity concentration of the species,φ
is the solid angle suspending the area of influence, θ is the angle of incidence ranging from
normal incidence (0°) to critical angle (θC), r is the radial distance from the point of emission,
R E is the range of the alpha particle corresponding to its max energy and RL, R U are the
lower and upper cut off ranges for track registration for an incident angle θ The integration
extends over a region of influence, which is constructed by using detailed track development
model. Eappen et al (2004) have discussed the typical regions of influence for
220

Rn and

Rn and their progenies in bare mode exposure configuration. Authors have showed that the

region of influence is located farther from the detector for
222

222

220

Rn progeny as compared to

Rn and its progeny concentrations. For the cup mode exposure, integrations over the

regions of influence would also include surface deposited activity contributions from the
inner walls of the dosimeter.
A code has been written in FORTRAN for calculating the calibration factors in different
configurations using the theoretical model (Eappen et al, 2001). Several experimental studies
were carried out in the calibration facility to determine the calibration factors under various
equilibrium factor and gas concentration conditions. Theoretical and the experimental CFs
obtained for the cup mode and bare mode exposures show close agreement with each other.

Dosimetric Methodology
Inter-laboratory standardization experiments for the etching characteristics conducted by all
the participants using standard alpha source also showed good agreements. A theoretical
methodology has been developed for evaluating the progeny concentrations using the twin
cup

222

Rn -

220

Rn dosimeter system (Mayya et al, 1998). The mathematical basis used is

similar to that developed by Planinic and Faj (1990, 1991) for radon dosimetry in which an
auxiliary parameter, ventilation rate, was extracted from the equations relating the bare
detector track densities to the gas and progeny levels. This approach is considered as most
logical one for

222

Rn -

220

Rn dosimetry with bare and cup detector system. But this

methodology is complicated in the mixed field situation by the fact that

220

Rn contribution

has to be given as its ventilation dependant spatial profile for which only limited information
is available in literature. So the data currently available in the literature are used for the
parameters like wall loss rates, unattached fractions and indoor turbulence levels
(Porstendorfer, 1994). In this method, it is assumed that SSNTD kept in the bare mode
responds only to the airborne alpha emitters and not to the alpha activity deposited on it. It is
also assumed that the bare card calibration factors are same for alpha emitters since it is a

9

function of only the difference in the ranges, lower and upper cut off energy of the detector.
Let T1, T2 and T3 be the track densities recorded in the membrane mode, filter mode and bare
mode, respectively. Let and kR be the calibration factors for

222

Rn gas in membrane

compartment and filter compartment, respectively and kT be the calibration factor for 220Rn in
the filter compartment. If d is the duration of exposure (days), the gas concentrations of 222Rn
(Bq m-3) and

220

Rn (Bq m-3) the vicinity of the dosimeter can be determined from the

observed track densities T1 and T2 using the following equations:
CR =

Since the

222

T1
dk R

and

CT =

T2 ! dCR k R
dkT

Rn decay constant is far smaller than the usually encountered air change rates

(ventilation rates), 220Rn may be assumed to be spatially uniform. The activity fractions of the
progeny are governed by their wall loss rates for the fine and the coarse fractions and the
ventilation rates. The bare track densities are also dependent on the ventilation rates, which
represent the progeny fractions for both gases. However unlike 222Rn,

220

Rn is not uniformly

distributed in the room due to its short half-life, but is expected to set up profiles (Doi and
Kobayashi, 1994). The concentration CT would be considerably lower than that present near
the ground and the walls, which are the 220Rn emitting surfaces. On the other hand, the thoron
decay products,

212

Pb and 212Bi, being longer lived would mix more or less uniformly in the

room and their activities will be fractions of a representative average

220

Rn concentration. A

turbulent-diffusive transport model developed by Mayya et al, (1998) was used to obtain the
bare track densities in terms of this concentration and the indoor ventilation rates. This
method, which is known as the root finding method (RFM), is theoretically the most
satisfactory approach for determining 222Rn,

220

Rn concentrations and their progeny working

levels using the tracks recorded on the three SSNTD films. The progeny working levels were
evaluated using the following relations:
WLR =

CR FR CR (0.104 FRA + 0.518 FRB + 0.37 FRC )
=
3700
3700

WLT =

CT FT
275

=

CT (0.908 FTB + 0.092 FTC )
275

where FR and FT are the equilibrium factors for 222Rn and 220Rn progeny, respectively, which
are related to the ventilation rate. However, in practice, it was found that small uncertainties
in the recorded tracks propagate non-linearly leading occasionally to unacceptable solutions
for the equilibrium factors. Very rich experience in measurements is required to eliminate

10

these uncertainties, which is expected to be realized in the coming few years. Until then, it
was decided to estimate the progeny concentrations using the cup based gas concentrations
and the universally accepted equilibrium factors published elsewhere (UNSCEAR, 2000).
Information obtained from the third SSNTD is being used in conjunction with the RFM for
building a database on the equilibrium factors. At present, the effective dose rate due to
inhalation was estimated from the

222

Rn,

220

Rn and progeny concentrations using the

UNSCEAR (2000) equilibrium factors as given in Table 8.

Inhalation Dose
Absorbed dose rates to the critical cells of the respiratory tract due to

222

Rn,

220

Rn and their

progeny can be estimated on the basis of aerosol characteristics, its size distribution,
unattached fraction, breathing fraction, and fractional deposition in the airways, mucous
clearance rate and location of the target cells in the airways. Several models have been
developed to assess the inhalation dose rates to the population due to

222

Rn,

220

Rn and their

progeny (Jacobi, 1993; Subba Ramu, 1988). Lung dose distribution assessment carried out by
different agencies from the year 1956 to 2000 show a large variation in dose conversion
factors (UNSCEAR, 1993, 2000). The estimated dose conversion factors varied drastically
based on the breathing rate as well as the target tissue mass. In the present study, the dose
conversion factors reported by UNSCEAR (2000) have been used to estimate the indoor
inhalation dose rates D (µSvh-1) due to 222Rn, 220Rn and their progeny as shown below:
D = 10!3[(0.17 + 9 FR )CR + (0.11 + 40 FT )CT ]

Numerical values given in the above relations are the dose conversion factors for gas and
progeny concentrations.

Results and Discussion
Present survey covers 25 locations in different parts of the country. This database alone was
not sufficient for obtaining a comprehensive mean value of the indoor 222Rn and 220Rn levels
on a national scale. Hence, similar data generated and published by this centre as well as
published by several groups elsewhere have also been used for the purpose. This data
includes mainly the indoor

222

Rn levels and the equilibrium factors estimated earlier survey

using single cup dosimeter covering more than 90 locations (UNSCEAR, 1993) and the data
generated from the survey carried out around 12 nuclear installations in India using the twin
chamber

222

Rn /220Rn dosimeters (Ramachandran et al, 1995). In the case of

220

Rn, the data

11

generated from 25 locations under this study and the data generated from the survey carried
out around nuclear installations in India were used.

Indoor 222Rn and 220Rn Level
Estimated levels of indoor 222Rn and the equilibrium factors between 222Rn and its progeny in
105 houses of different types of construction at 84 locations in different parts of India by the
single cup method are given in Table 9. The estimated 222Rn level at different locations varies
from 6.4 Bqm-3 to 95.4 Bq m-3 with a geometric mean of 25.5 Bq m-3 (GSD 2.1). Equilibrium
factors were estimated using the bare detector exposure mode along with the cup with
membrane mode in these locations for

222

Rn progeny. From the calibration factors for the

bare detector, the progeny concentrations are evaluated and the equilibrium factors were
estimated using the standard equation. Equilibrium factors for

222

Rn progeny range between

0.21 and 0.95 (UNSCEAR, 1993) with a geometric mean of 0.54 (GSD 1.4). Estimated mean
equilibrium factors range between 0.1 and 0.9, but most of the values are found to be within
30% of the typical value of 0.4 used by the UNSCEAR (1993) for inhalation dose
calculations. Values thus computed using the standard relation is not strictly correct, since the
bare detector exposure is not a function of WL, but depends on the F factor.
A theoretical methodology has been developed incorporating this fact to extract the modified
F values. Using this concept, the revised F values were evaluated and these values are found
to vary from 0.12 to 1.2 with a median of 0.46 ± 0.2. Although, the median value of F is
found to decrease in the revised estimates, the spread is found to be higher. Besides, the
distribution is found to be skewed to the left, unlike the near symmetrical form shown by the
pre-revised data in Fig.1. Mathematical analysis of the F distribution shows that the F
values correspond to a mean ventilation rate of 2 per hour with a GSD of 3 (UNSCEAR,
1988).
Results on the indoor 222Rn, 220Rn levels and the estimated inhalation dose rates are presented
in Table 10. The geometric mean 222Rn levels at different locations range between 4.6 Bq m-3
and 147.3 Bq m3. The estimated geometric means of indoor

220

Rn levels at these locations

range between 3.5 and 42.8 Bq m-3. Fig. 2 shows the lognormal distribution of indoor

222

Rn

-3

levels at different locations in India, which gives a geometric mean of 23.0 Bq m (GSD
2.61). The lognormal distribution pattern of indoor

220

Rn levels is shown in Fig. 3 with the

geometric mean of 12.2 Bq m-3 (GSD 3.22). In view of the large number of measurements
carried out, the distributions pattern estimated can confidently be projected as national
representations of indoor

222

Rn and

220

Rn levels in India. The relationship between indoor

12

222

Rn and 220Rn levels is indicated in Fig.4, which shows a good correlation between the two

quantities. The relationship indicates that, in general, the indoor thoron concentration is about
50% of that due to indoor

222

Rn concentration, which is not trivial as considered earlier. All

the data from the present study as well as other relevant data mentioned in this report have
been used for preparing the maps of indoor

222

Rn and

level. Fig. 5 and 6 illustrate these maps of indoor

222

220

Rn concentrations on a national

Rn and

220

Rn levels respectively to

represent the different concentration levels.
222

Rn level dependencies on different types of dwellings

The variation of indoor 222Rn levels in various types of dwellings is examined using the data
and the results are presented in Table 11. A scrutiny of this table reveals that the 222Rn levels
are higher in houses constructed with plastered whitewashed walls and mosaic floors. Houses
having wooden walls show lowest 222Rn levels. It can be noticed that irrespective of the type
of walls, houses constructed with tile flooring show lower 222Rn levels. An analysis has been
carried out to evaluate the statistical significance (95% confidence limits) of the difference in
means of the indoor

222

Rn levels among different dwelling types and the results are given in

Table 12. This is based on the assumption that the

222

Rn levels follow a normal distribution

and that there is not much variation in the ventilation rates in dwellings. Although this
analysis does not include all the geographical factors that govern the pattern of radon levels,
it provides a general representation for the variation of indoor
dwellings. Table 12 shows that the differences in the

222

222

Rn levels in Indian

Rn levels among different types of

floors are small or insignificant when the walls are plastered and painted. This shows that
most of the 222Rn emanates from the walls and painted walls will reduce the 222Rn emanation.
When the walls are of plastered and whitewash type, there are significant differences between
mosaic and any other floor types. Also, whenever mosaic floors are used, the differences are
significant between different types of walls. Hence this analysis shows that the combination
of whitewash walls and mosaic floors may lead to higher levels of indoor
the reason for this high

222

222

Rn. However,

Rn levels in dwellings having this combination is not obvious from

the present set of data. More detailed investigation and categorization are needed in this
respect.

Estimation of Ventilation Rates
Several methods such as tracer gas techniques and SSNTD based techniques are being used
to estimate the ventilation rates in dwellings. Usual method of determining the ventilation
rate in a room involves the measurement of the rate of loss of a tracer gas from the room.
13

Various tracer gases like CO2, nitrous oxides and 85Kr are being used for these measurements.
The diurnal variations of indoor radon levels also can be used to estimate the ventilation rate
in rooms (Ramachandran, 2001; Shaikh et al, 1992).

222

Rn and its short-lived progenies,

which are naturally present in air, are also being used as a tracer. In the SSNTD based
techniques,

222

Rn gas and progeny concentrations are estimated in rooms using SSNTD

dosimeters in membrane and bare modes of exposure on a time integrated scale. For steadystate
222

222

Rn and its progeny levels, the ratio of the working level (progeny concentration) to

Rn gas concentration (Bq m-3) is evaluated. This ratio is related to the pseudo-ventilation

rate and plate-out rate.
Actual ventilation rate is obtained by subtracting the plate-out rates of attached and
unattached fractions of

222

Rn daughters from the pseudo-ventilation rates. The ventilation

rates estimated by earlier investigations (Shaikh et al, 1992) in Indian dwellings using this
method are given in Table 13. The measured ventilation rates varied between 0.42 and 4.46 h1

with a mean of 2.08 h-1 (standard deviation of 49%). With respect to the type of dwellings,

the ventilation rates varied from 0.42 to 2.82 h-1 in Chawls and from 0.52 to 4.46 h-1 in flats.
This wide variation is acceptable due to differences in construction and atmospheric
conditions. Ventilation rates in some other countries like UK and USA range from 0.93 to
2.89 h-1 and 0.03 to 1.16 h-1 respectively (Nero et al, 1983; Israeli, 1985). Being in the
temperate region, Indian dwellings are expected to have higher ventilation rates compared to
dwellings in cold regions.

Inhalation Dose Rates
The 222Rn,

220

Rn and their progeny concentrations are converted into inhalation dose rates to

residents using the above equation and the results are presented in Table 10. This table
includes contributions from

222

Rn and progeny as well as

220

Rn and progeny. The total

estimated inhalation dose rates vary from 0.27 m Sv y-1 at Kalpakkam to 5.14 m Sv y-1 at
Digboi with a geometric mean value of 0.97 m Sv y-1 (GSD 2.49). Inhalation dose rates due
to

222

Rn and its progeny show a geometric mean value of 0.63 m Sv y-1 (GSD 1.52), while

that due to 220Rn and its progeny show a geometric mean value of 034 m Sv y-1 (GSD 1.44).
It can be seen from this table that the dose due to

220

Rn and progeny is about half of that due

to 222Rn and progeny. This fact is illustrated in Fig.7, which shows good correlation between
the total indoor inhalation dose and that due to
inhalation dose rate due to

220

220

Rn and its progeny. Contribution of

Rn and its progeny is seen to be nearly 17% of the total

inhalation dose rate. Nambi et al, (1986) estimated the average external gamma radiation

14

dose rate in India as 0.80 m Sv y-1 based on TLD measurements. These data suggest that in
normal background areas, the inhalation dose rates predominate over the external gamma
dose rates. The distribution pattern of indoor inhalation dose rates is depicted in Fig.8, which
is a lognormal distribution. The majority of measurements indicate that indoor inhalation
dose rates range between 0.1 and 2.5 mSv y-1. The geographical variation of indoor inhalation
dose rates is also of considerable interest. This information can be used to delineate the
normal and high background radiation areas. Though the present survey data is not sufficient
for such an exercise, an effort has been made to study the geographical variation of the indoor
inhalation dose rates in India is depicted in Fig.9. This figure shows that about 11 locations
record dose rates above 1 mSv y-1 and most of these locations lie in the northeastern part of
the country.

Remedial Action Levels
Elevated levels of indoor

222

Rn may be encountered in work places other than uranium or

non-uranium mines as well. An issue of concern today is to prescribe action levels (in terms
of average indoor levels) above which intervention would be desirable to reduce the levels of
human exposure. Action level is defined as the level of dose rate or activity concentration
above which remedial actions or protective actions should be carried out in chronic exposure
or emergency exposure situation. Choice of the action level is complex depending not only
on the level of exposure but also on the likely scale of action, which has economic
implications for the community and for the individuals (IAEA, 1994; ICRP, 1991). ICRP
(1993) made a distinction between the existing exposure situations, where any action would
have to be remedial, and future situations, which can be subjected to limitation and control at
the stage of decision and planning. In this connection, it is pointed out that the distribution
pattern of indoor

222

Rn follows a lognormal distribution, which means that there would be a

very small fraction of the total that would have large values. The geometric mean and
geometric standard deviation are appropriate for characterizing this type of distribution.
Knowing the geometric mean and geometric standard deviation, it is possible to predict what
fraction of the total population would exceed a given value of the parameter. ICRP (1993) has
recommended that there is considerable merit in the definition of radon-prone areas so as to
focus attention where it is most exigent and on action where it is most effective. A

222

prone area may be defined as the one in which about 1% of the buildings has

222

Rn

Rn

concentrations above 200 Bq m-3. The recommended action level is 200 Bq m-3 for such a
building, which would correspond to an annual effective dose of 5 mSv. On the other hand,

15

UNSCEAR (1993) recommends an action level of 400 Bq m-3.The international
recommendations for

222

Rn action levels are given in Table 14 (Sohrabi, 1997). The results

presented here, show that the indoor

222

Rn levels in India are far below the action levels.

Hence, it is clearly demonstrated that most of the dwellings in India do not warrant any action
level with respect to indoor
concentrations levels for

222

Rn levels. As per the new WHO recommendations the

222 Rn

and

220 Rn

are 200 and 100 Bq m-3, respectively. But,

the study raises some concern about the high inhalation dose rates observed at the
northeastern parts of the country.

Conclusions
A countrywide survey on

222

Rn and

220

Rn levels for India has been carried out in dwellings

using Solid State Nuclear Track Detector based passive detector technique. A good database
on the total external radiation across the country is supplemented with the inhalation
component, which is mainly contributed by

222

Rn and

220

Rn and their progeny. Calibration

factors for the measurements have been derived experimentally as well as theoretically. The
results show that the

222

Rn gas concentrations at different locations vary between 4.6 and

147.3 Bq m-3with an overall geometric mean of 23.0 Bq m-3 (GSD 2.61).

220

Rn gas

concentrations are found to be less than the 222Rn gas concentrations at these locations (3.5 to
42.8 Bq m-3) with an overall geometric mean concentration of 12.2 Bq m-3 (GSD 3.22). The
inhalation dose rates due to

222

Rn,

220

Rn and their progeny ranged from 0.27 m Sv yr-1 at

Kalpakkam to 5.14 m Sv yr-1 at Digboi with a geometric mean value of 0.97 m Sv yr-1 (GSD
2.49). In general, the indoor

220

Rn and progeny concentrations and corresponding inhalation

dose rates are found to be about half of that due to

222

Rn and its progeny. The geographical

distribution pattern shows comparatively high inhalation dose rates (> 2.0 m Sv yr-1) in the
northeastern part of India, which is supported by observations of high concentration of
uranium, and thorium in soil and rocks in this region. The study also reveals that most of the
dwellings in India do not demand any action levels with respect to indoor 222Rn and 220Rn due
to good ventilation prevailing in Indian dwellings. However, it raises some concern about the
high inhalation dose rates observed in the northeastern part of the country.

16

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20

Table Caption
Table 1: Natural Radioactivity Content in Indian Building Materials
Table 2: Natural Radioactivity Content in Indian soil
Table 3: Uranium, Thorium and Potassium Content in Indian Rocks
Table 4: Volume Specific Entry Rate and indoor Radon Levels from Various Sources
Table 5: Reported Indoor 222Rn Levels Around the World
Table 6: Outdoor and Indoor 220Rn Levels around the World
Table 7: Calibration Factors (CFs) for the Cup Mode and Bare Mode Exposures
Table 8: Average concentration of 222Rn, 220Rn and their progeny in air and corresponding annual
effective doses
Table 9: Indoor 220Rn levels and equilibrium factors in Indian dwellings using Cup dosimeter
Table 10: Indoor 222Rn, 220Rn levels and Inhalation Doses
Table 11: 222Rn levels in different types of dwellings
Table 12: Statistical significance between radon level and type of dwelling
Table 13: Ventilation Rates in Indian Dwellings
Table 14: Action Levels Reported in Literature

21

Table 1: Natural Radioactivity Content in Indian Building Materials (Menon et al 1987)
40

Material
Cement
Brick
Stone
Sand
Granite
Clay
Fly ash
Lime stone
Gypsum

5
130
48
5
76
6
6
6
70

226

K

- 385
- 1390
- 1479
- 1074
- 1380
- 477
- 522
- 518
- 807

232
Ra
Th
Radium
equivalent
Bq kg-1
16 - 377
8 - 78 40 - 440
21 - 48 26 - 126 88 - 311
6 - 155
5 - 412 24 - 311
1 - 5047 4 - 2971 22 -7759
4 - 98 103 - 240 25 - 525
7 - 1621 4 - 311 11 -1865
7 - 670 30 - 159 56 - 773
1 - 26 1 - 33 5 - 148
7 - 807 1 - 152 59 - 881

Table 2: Natural Radioactivity Content in Indian soil
(Mishra et al 1971; Sadasivan et al 2003)
232

Location
Ahmedabad
Aligarh
Bangalore
Bhopal
Bikanir
Mumbai
Kolkatta
Cherrapunji
Chingalput
Coimbatore
Cuttack
Darjeeling
Dehradun
Delhi
Dhanbad
Gangtok
Gulmarg
Hyderabad
Jaduguda
Jaipur
Jasilmar
Jamnagar
Jodhpur

Th

226

40

Ra

K

-1

Bq kg
53.0
82.0
16.9
15.7
11.7
13.5
24.1
17.4
120.5
10.1
61.7
24.8
22.6
19.9
37.1
23.9
20.1
45.9
41.0
14.9
37.1
3.8
13.1

24.8
54.4
15.2
11.8
8.8
9.4
20.4
21.5
22.9
10.2
15.3
2417
25.9
19.2
53.0
26.1
15.9
15.2
179.1
11.6
49.0
2.9
10.7

526.6
530.1
486.7
376.8
439.6
169.6
662.9
37.7
408.2
266.9
722.2
678.2
803.8
536.9
345.4
854.1
555.8
1073.4
455.3
505.5
565.2
56.5
458.9

232

Location
Kanpur
Kharagpur
Kakrapar
Chennai
Mangalore
Meerut
Nagpur
Nainatal
Nasik
Ooty
Poona
Ranchi
Shillong
Srinagar
Tehri
Thiruvalla
Trivandrum
Tiruchirapali
Visakapatnam
Udagamandalam
Jhansi
Kaiga
Thumba

Th

226

40

Ra

K

-1

Bq kg
23.8
18.4
12.4
23.1
13.5
22.0
16.5
24.8
34.4
3.4
4.2
22.4
23.9
18.6
136.2
74.3
53.2
47.8
24.8
43.2
12.6
12.4
27.5

24.0
15.2
12.2
6.7
9.3
22.7
11.8
24.7
18.6
2.5
3.0
24.4
15.5
14.8
81.6
19.8
20.3
2070
163.2
114.6
20.4
12.2
8.9

850.9
72.2
94.4
766.2
151.2
112.3
307.7
979.7
290.6
87.8
87.9
1055.0
323.2
615.4
328.2
25.1
37.7
509.4
376.8
272.6
518.2
94.2
-----

22

Table 3: Uranium, Thorium and Potassium Content in Indian Rocks
(Sankaran et al 1986)
228

State

232

U

Th

Potassium (%)
Bq kg

Andaman & Nicobar
Andhra Pradesh
Arunachal Pradesh
Assam
Bihar
Daman & Diu
Delhi
Goa
Gujarat
Haryana
Himachal Pradesh
Jammu & Kashmir
Karnataka*
Kerala
Madhya Pradesh
Maharashtra
Manipur
Meghalaya
Mizoram
Nagaland
Orissa
Pondicherry
Punjab
Rajasthan
Tamil Nadu
Tripura
Uttar Pradesh
West Bengal

31.5
33.2
34.9
63.0
40.9
55.7
32.6
33.0
55.7
32.6
32.6
43.4
33.0
45.1
44.0
31.7
95.2
66.7
35.5
89.1
35.4
27.4
32.6
36.7
27.4
33.1
32.9
47.9

40

K

-1

27.4
40.9
98.2
129.3
36.9
24.5
30.4
30.5
24.5
30.4
30.4
29.0
30.5
47.6
31.6
33.4
36.2
32.0
28.8
39.5
110.3
33.1
30.4
32.1
33.1
28.5
33.8
45.1

1.22
1.65
2.00
2.41
1.62
1.63
1.87
1.33
1.63
1.87
1.87
1.76
1.33
1.80
1.48
1.64
1.63
1.67
1.87
2.00
1.61
1.52
1.87
1.64
1.52
1.55
2.03
1.86

378.2
511.5
620.0
747.1
502.2
412.3
579.7
412.3
505.3
579.7
579.7
545.6
412.3
558.0
458.8
508.4
505.3
517.7
579.7
620.0
499.1
471.2
579.7
508.4
471.2
480.5
629.3
576.6

Table 4: Volume Specific Entry Rate and indoor 222Rn Levels from
Various Sources (ICRP 1986)
Specific entry rate
(Bq m–3 h–1)
Source
Brick or concrete
Wooden Houses
Soil
Outdoor air
Others (walls, natural gas)
All sources

Estimated mean Range
2-20
<1
1-40
2-5
< 0.1
6-60

1-50
0.05-1
0.5-200
0.3-15
0.01-10
2-200

Indoor 222Rn concentration
*(Bq m–3)
Estimated
Range
mean
3-30
0.7-100
<1
0.03 - 2
2-60
0.5-500
3-7
1-10
<0.1
0.01-10
10-1000
2-500

* Mean ventilation rate used is 0.7 h–1 (normal range 0.3 – 1.5 h–1)

23

Table 5: Reported Indoor 222Rn Levels Around the World (UNSCEAR 2000)
Concentration (Bq m–3)
AM GM MAX GSD
Africa
Algeria
30
140
Egypt
9
24
Ghana
340
North America
Canada
34
14
1720
3.6
United States
46
25
3.1
South America
Argentina
37
26
211
2.2
Chile
25
86
Paraguay
28
51
East Asia
China
24
20
380
2.2
Hong Kong
41
140
India
57
42
210
2.2
Indonesia
12
120
Japan
16
13
310
1.8
Kazakhstan
10
6000
Malaysia
14
20
Pakistan
30
83
Thailand
23
16
480
1.2
West Asia
Armenia
104
216
1.3
Iran
82
3070
Kuwait
14
6
120
Syria
44
520
North Europe
Denmark
53
29
600
2.2
Estonia
120
92
1390
Finland
120
84 20000
2.1
Lithuania
55
22
1860
Norway
73
40 50000
Sweden
108
56
3900
West Europe
Austria
15
190
Belgium
48
38 12000
2.0
France
62
41
4690
2.7
Germany
50
40 >10000 1.9
Ireland
37
1700
Luxemburg
110
70
2500
2.0
Netherlands
23
18
380
1.6
Switzerland
70
50 10000
U.K
20
10000
East Europe
Bulgaria
22
250
Czech Republic 140
20000
Hungary
107
82
1990
2.7
Poland
41
32
432
2.0
Romania
45
1025
Slovakia
87
3750
South Europe
Albania
120 105
270
2.0
Croatia
35
32
92
Cyprus
7
7
78
2.6
Greece
73
52
490
Italy
75
57
1040
2.0
Portugal
62
45
2700
2.2
Slovenia
87
60
1330
2.2
Spain
86
42 15400
3.7
Oceania
Australia
11
8
420
2.1
New Zealand
20
18
90
Median
46
37
480
2.2
Population weighted average
39
30
1200
2.3
Region

Country

24

Table 6: Outdoor and Indoor 220Rn Levels around the World (UNSCEAR 2000)
Country

North America
United States of America
China
Hong Kong
Japan
Malaysia
France

Equilibrium equivalent concentration 220Rn/222Rn EEC ratio
(Bq m–3)
Outdoor
Indoor
Outdoor
Indoor
0.5
0.04
0.09
(0.03-4.7)
(0.03-0.3)
0.4
0.3
(0.1-0.5)
009
(0.03- 0.12)
0.5
(0.3-1.8)
-

United Kingdom

-

Germany

-

Republic of Moldova
Romania
Russian Federation
Italy
Slovenia
Range

0.2
0.3
(0.1-0.6)
0.12
(0.05 - 0.37)
(0.09 - 0.5)

0.2
(0.1-0.3)
0.8
0.8
(0.4-1.2)
0.7
(0.04-2.1)
1.1
(0.4-2.1)
0.8
(0.6-13.3)
0.3
(0.07-1.1)
0.5
(0.1 -1.0)
1.0
(0.1 -6.4)
1.1
(0.1-6.4)
(1.1-7 .1)
12
(0.5-76)
-

0.013

(0.2 -12)

0.01- 0.08

0.05
0.04

0.07
0.06

-

0.2

0.08

0.08

-

0.03

-

0.02

-

-

0.04

0.05

0.05

0.04

-

0.09
(0.02 - 0.24)
0.11
(0.01 - 0.38)

-

0.01- 0.5

25

Table 7: Calibration Factors (CFs) for the Cup Mode and Bare Mode Exposures
(Mayya et al 1998; Eappen et al 2004)
Mode of Exposure

222

Filter

Calibration Factors
(Tr cm–2/Bq d m-3) for
Rn
Membrane

220

Rn

Filter

Membrane

Cup Mode Exposure
Experimental
Theoretical
Bare Mode Exposure

0.02 ± 0.004 0.019 ± 0.003 0.017 ± 0.003 0.016
0.021

Experimental
Theoretical

-

0.0
-

0.020 ± 0.002

0.019 ± 0.003

0.019

0.019

Table 8: Average concentration of 222Rn, 220Rn and their progeny in air and
corresponding annual effective doses (UNSCEAR 2000)

Radionuclide

Radon
Total
Thoron

Location

Concentration
(Bq m–3)

Effective dose
equivalent
(mSv/ Bq h m–3)

Annual effective dose
(µ Sv)

Gas

EEC+

Gas

EEC

Gas

EEC

Outdoor
Indoor

10
40

6
16

0.17
0.17

9
9

3
48

Outdoor
Indoor

10
10

0.1
0.3

0.11
0.11

40
40

2.0
8.0

95
1009
1155
7.0
84
101
1256

Total
Total Annual Effective Dose Equivalent Due to 222Rn and 220Rn (µ Sv)
+

This is the equilibrium equivalent concentration (EEC) of radon/thoron and is the product of the concentration
of radon/thoron and the equilibrium factor between radon/ thoron and its decay products. The equilibrium factor
has been taken as 0.6 for outdoor and 0.4 for indoor in the case of radon. In the case of thoron F is taken as 0.01
for outdoor and 0.03 for indoor. These values are weighted for an occupancy factor of 0.2 for outdoor and 0.8
for indoor.

26

Table 9: Indoor 222Rn levels and equilibrium factors in Indian dwellings using
Cup dosimeter (Ramachandran et al 1995)
State
Andhra Pradesh
A & Nicobar
Arunachal Pradesh
Assam
Bihar
Chaidigarh
Delhi
Ooa
Gujarath
Haryana
Himachal Pradesh
Karnataka
Kerala
Maharashtra
Madhya Pradesh
Meghalaya
Orissa
Punjab
Pondicheery
Rajashtan
Sikkim
Tripura
Tamil Nadu
Uttar Pradesh
West Bengal

Sites
5
1
1
2
9
1
1
1
3
2
3
6
9
5
2
2
3
4
1
2
1
I
11
6
3

Radon levels (Bq m–3)
Equilibrium factor
No. of
houses MAX MIN GM GSD MAX MIN GM GSD
5
1
1
5
15
1
1
1
3
4
3
6
9
5
2
2
12
4
1
2
1
1
11
6
3

41.8
15.6
27.6
88.7
92.6
29.9
39.8
23.4
26.4
96.8
43.6
56.9
51.3
35.2
45.8
33.7
64.8
93.0
14.2
66.9
55.9
59.3
51.9
95.4
95.4

6.4
10.0
16.9
43.7
7.4
19.3
12.7
8.8
9.4
7.0
10.4
16.7
7.1
7.6
12.2
11.6
14.6
9.0
6.9
7.9
25.1
25.1
5.9
10.5
6.4

17.5
13.4
20.6
67.6
40.9
25.6
18.4
15.5
15.0
32.1
18.3
14.9
17.0
21.2
21.3
17.3
30.1
44.7
9.9
21.4
38.3
40.0
15.3
27.0
25.5

1.7
1.2
1.2
1.1
1.9
1.2
1.4
1.4
1.4
2.6
1.4
1.6
1.6
1.4
1.5
1.4
1.6
2.2
1.3
2.3
1.3
1.5
1.7
1.8
2.1

0.93
0.58
0.35
0.87
0.92
0.42
0.90
0.59
0.94
0.85
0.80
0.86
0.95
0.88
0.67
0.92
0.67
0.87
0.63
0.77
0.34
0.59
0.75
0.81
0.95

0.27
0.46
0.24
0.48
0.32
0.33
0.36
0.42
0.39
0.36
0.36
0.29
0.21
0.30
0.32
0.30
0.21
0.30
0.42
0.26
0.31
0.28
0.20
0.31
0.21

0.46
0.51
0.29
0.67
0.61
0.36
0.59
0.53
0.65
0.54
0.57
0.46
0.51
0.48
0.44
0.48
0.42
0.55
0.48
0.44
0.32
0.41
0.44
0.54
0.54

1.4
1.1
1.2
1.1
1.2
1.1
1.4
1.2
1.3
1.4
1.3
1.4
1.5
1.3
1.3
1.5
1.4
1.4
1.2
1.5
1.0
1.3
1.3
1.3
1.4

27

Table 10: Indoor 222Rn, 220Rn levels and Inhalation Doses
222

No

Location

No. of
Houses

Rn
(Bq m–3)
GM
GSD

01
Patiala
91
11.2
02
Chandigarh
40
15.9
03
Palanpur
30
29.2
04
Amritsar
70
14.0
05
Hamirpur
29
48.8
06
Tehri
121
41.6
07
Kumaun Hill
68
18.9
08
Hyderabad
72
4.6
09
Secunderabad
80
48.5
10
Chennai
100
14.3
11
Chennai suburbs
113
15.1
12
Kalpakkam
42
6.3
13
Mysore
70
21.5
14
Mysore surburbs
106
9.7
15
Kamptee
12
8.7
16
Nagpur
84
54.3
17
Guwahati
48
48.1
18
Shillong
29
59.7
19
Karimganj
7
37.6
20
Kailash sahar
5
31.3
21
Itanagar
65
41.1
22
Mizoram
17
27.6
23
Namrup
10
147.3
24
Digboi
20
60.5
25
Agarthala
57
34.7
222
–3
Mean Rn concentration (Bq m )
220
Mean Rn concentration (Bq m–3)
Mean total inhalation dose rate (mSv y–1)

2.2
1.7
1.7
2.0
1.8
1.7
1.5
2.1
2.1
2.3
1.7
1.8
2.7
2.7
2.3
3.3
1.7
2.0
1.5
1.6
1.7
1.7
1.4
1.7
1.7

220

Rn
(Bq m–3)
GM
GSD
6.3
8.4
14.6
7.8
32.3
13.1
21.1
3.5
34.0
6.4
13.5
5.7
19.6
11.4
6.1
15.1
25.4
29.5
10.2
15.5
28.6
12.1
23.6
42.8
18.3

2.7
2.4
2.4
2.7
2.4
2.2
2.1
3.3
3.3
3.3
2.1
1.9
3.1
3.1
2.9
4.2
1.7
2.1
1.7
1.9
1.8
2.0
2.1
2.3
2.1

Inhalation dose
(mSv y–1)
222
220
Rn +
Rn +
Progeny
Progeny
0.37
0.07
0.53
0.10
0.96
0.17
0.46
0.09
1.61
0.37
1.37
0.15
0.62
0.24
0.15
0.04
1.60
0.39
0.48
0.08
0.50
0.16
0.21
0.07
0.71
0.23
0.32
0.13
0.29
0.07
1.79
0.17
1.59
0.29
1.97
0.34
1.24
0.12
1.03
0.18
1.36
0.33
0.91
0.14
4.87
0.27
1.15
0.21
0.21
0.07

Total
inhalation
Dose
(mSv y–1)
0.44
0.63
1.13
0.55
1.98
1.52
0.86
0.19
1.99
0.55
0.66
0.28
0.94
0.45
0.36
1.96
1.88
2.31
1.36
1.21
1.69
1.05
5.14
1.36
0.28
23.0
12.2
0.97

28

Table 11: 222Rn levels in different types of dwellings
Wall Type

Flooring

Bare
Plaster and painted

Cement
Cement
Mosaic
Tile
Stone
Cement
Mosaic
Wood
Tile
Cement
Mosaic

White washed

Wooden panel

No. of
houses

GM (AM)
(Bq m–3)

GSD(SD)

4
121
95
12
1
11
7
4
4
3
8

20.8 (21.6)
20.2 (23.4)
18.1(21.4)
12.9(13.5)
28.5 (28.5)
15.1 (18.5)
34.8 (38.9)
15.4(17.8)
12.1 (13.0)
10.8 (10.9)
13.7(13.9)

1.3 (7.0)
1.7 (13.2)
1.8 (13.2)
1.4 (4.0)
1.0 (0.0)
1.8 (14.9)
1.7 (18.0)
1.7 (11.9)
1.5 (4.8)
1.1 (1.4)
1.2 (2.9)

Table 12: Statistical significance between radon level and type of dwelling
Wall

Plaster and
paint

Plaster and
whitewash

Wood

Floor
Cement
Mosaic
Cement
Tile
Mosaic
Tile
Mosaic
Cement
Cement
Tile
Mosaic
Wood
Mosaic
Tile
Wood
Tile
Mosaic
Cement

Floor
Cement

Mosaic floor

Wall
Plaster/paint
Plaster/whitewash
Plaster/whitewash
Plaster/paint
Plaster/whitewash
Wood

Difference of
means

Statistical
estimate

95 %
Confidence
limits

Remarks

2.00

2.30

-2.5 to 6.5

No
difference

9.90

1.66

6.7 to 13.8

Small
difference

7.90

2.28

3.4 to 12.3

Small
difference

20.40

8.15

4.1 to 36.4

Significant
difference

5.50

5.09

-4.5 to 15.5

No
difference

21.10

9.04

3.4 to 38.3

Significant
difference

25.90

7.21

11.8 to 40.0

Significant
difference

4.80

6.42

-7.8 to 17.4

No
difference

3.00

1.31

0.4 to 5.6

Small
difference

Difference of
means

Statistical
estimate

95 %
Confidence
limits

Remarks

4.90

4.65

-4.2 to 14.0

No
difference

17.50

7.08

3.6 to 37.4

Significant
difference

25.00

6.89

11.5 to 38.5

Significant
difference

29

Table 13: Ventilation Rates in Indian Dwellings (Shaikh et al 1992)
Actual
* Mean ventilation
ventilation rate
rate (h–1)
(h–1)

Type of
dwelling

Pseudo ventilation
Rate (h–1)

Plate out rate (h–1)

Chawl

3.9

1.43

2.43

2.4

1.07

1.33

1.5
3.7
3.7
2.1

1.10
0.90
1.43
1.02

0.42
2.82
2.27
1.08

5.0

1.38

3.62

4.5

2.61

1.89

4.7

2.73

1.97

4.9

2.59

2.31

3.0
2.5
3.6
6.7
3.3
2.8
5.5

1.02
1.98
1.45
2.24
1.69
1.76
2.08

1.98
0.52
2.15
4.46
1.61
1.04
3.42

3.7

1.65

2.05

Bungalow

A/C room

Flat

1.73

2.76

2.14

2.15

30

Table 14: Action Levels Reported in Literature (Soharabi, 1997)
Country

Australia
Austria
Canada
Denmark

Action Level
( Bq m-3)
Old
New
Building
Building
200
200
400
400
800
200
200

Remarks and/or recommended time for remedial
action

…..
…….
…….
…….
A time frame band and on the basis of a life time (60
y) cumulative exposure of 15,000 Bq/m3 y; 10 times
higher than the UK (NRPB) level

Germany

250

250

Ireland

200

200

Sweden

200

70

Between 70 to 200 should be reduced by simple
measurements if possible

200

200

A time frame band on the basis of a life time (60 y)
cumulative exposure of 1500 Bq/m3 , a few years;
for 750 to 7500 Bq/m3, within a few months; above
7500 Bq/m3, immediate action or evacuation.

United States
ICRP 65
IAEA-BSS
CEC

150
200-600
200-600
400

150
200-600
200-600
200

WHO

200-300

200-300

United Kingdom

31

Figure Caption
Fig. 1: Frequency distribution of equilibrium factors
Fig. 2: Distribution pattern of indoor 222Rn levels
Fig. 3: Distribution pattern of indoor 220Rn levels
Fig. 4: Relation between indoor 222Rn and 220Rn concentrations
Fig. 5: Indoor 222Rn levels in India
Fig. 6: Indoor 220Rn levels in India
Fig. 7: Relation between total indoor inhalation dose rates and that due to
progeny

220

Rn and its

Fig. 8: Distribution pattern of total indoor inhalation dose rates
Fig. 9: Total indoor inhalation dose rates due to
locations in India

222

Rn,

220

Rn and their progeny at different

32

Fig. 1: Frequency distribution of equilibrium factors

33

Fig. 2: Distribution pattern of indoor 222Rn levels

34

Fig. 3: Distribution pattern of indoor 220Rn levels

35

Fig. 4: Relation between indoor 222Rn and 220Rn concentrations

36

Fig. 5: Indoor 222Rn levels in India

37

Fig. 6: Indoor 220Rn levels in India

38

Fig. 7: Relation between total indoor inhalation dose rates and that due to 220Rn and its
progeny

39

Fig. 8: Distribution pattern of total indoor inhalation dose rates

40

Fig. 9: Total indoor inhalation dose rates due to 222Rn, 220Rn and their progeny at different
locations in India

41