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 References Barillion R and Chambraudet (2000) Alpha particle dosimetry using solid state nuclear track detectors: Application to radon and its daughters, J Radio-anal and Nucl. Chem, 243, 607 620. Barretto PMC, Clark, Ronald B, and Adams JAS (1972) Physical characteristics of radon-222 emanation from rocks, soils and minerals: its relation to temperature and alpha dose, Natural Radiation Environment II, Conf-720805-P2, USERDA, New York, 731 -740. Campos-Venuti G, Janssens A and Olast M (1994) Indoor Radon Remedial Action, The Scientific Basis and the Practical Implications, Proceedings of the First International Workshop, Rimini, Italy, Rad. Prot Dos., 56(1-4): 133-135. discriminating dosimeter, Radiation Measurements 38, 5 – 17 Doi M and Kobayashi, S (1994) The passive radon-thoron discriminative dosimeter for practical use, Hoken Butsuri, 29, 155 - 166. Doi M, Fugimoto K, Koyabshi S and Yenhara, H (1994) Spatial distribution of thoron and radon concentrations in the indoor air of a traditional Japanese wooden house, Health. Phys, 66, 43 - 49. Durrani, S A, and Radomir Ilic (1997) Radon Measurements by Etched Track Detectors: Applications in Radiation Protection, Earth Sciences and the Environment, World Scientific, Singapore, 77 - 102. Eappen KP and Mayya YS (2004) Calibration factors for LR-115 (type-II) based radon thoron Eappen KP, Ramachandran TV, Shaikh AN and Mayya YS (2001) Calibration factors for SSNTD based radon / thoron dosimeters, Rad. Prot. and Environment. 410 - 414. Eappen, KP, Ramachandran, TV, Shaikh, AN and Mayya, YS (2001) Calibration factors for SSNTD based radon / thoron dosimeters, Rad. Prot. and Environment, 410 - 414 Fleischer RL, (1997) Radon: Overview of properties, origin and transport, In: Radon Measurements by Etched Track Detectors, Applications in Radiation Protection, earth Sciences and the Environment, (Eds.Durrani, S. A., and Ilic, R), World scientific, Singapore, 1 -20. Ilic R, and Suteg T (1997) Radon Monitoring devices based on Etched Track Detectors, In: Radon Measurements by Etched Track Detectors, Applications in Radiation Protection, earth Sciences and the Environment, (Eds,, Durrani, S. A., and Ilic, R), World Scientific, Singapore, 103 - 128. Ingersall JG (1983) A survey of radio nuclide constants and radon emanation rates in building materials used in the US., Health Phys, 45, 363-368. 17 International Atomic Energy Agency (1994) International Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, Safety Series No. 115 - 1, IAEA, Vienna International Commission for Radiation Protection (1986) Publication No. 50, Lung Cancer Risk from Indoor Exposures to Radon Daughters, Annals of ICRP 16, Pergamon Press, Oxford. International Commission for Radiation Protection(1993) Publication No. 65, Annals of ICRP 23, Protection Against Rn222 at Home and at Work., Pergamon Press, Oxford. International Commission for Radiation Protection. Recommendations, Pergamon Press, Oxford. (1991) Publication No. 60, Israeli M (1985) Deposition rates of radon progeny in houses, Health Phys, 49, 1969-1983. Jacobi W (1993) The history of the radon problems in mines and homes, Annals of the ICRP, 23(2), 39. Jha G, Raghavayya M, and Padmanabhan N (1982) Radon permeability of some membranes, Rad, Meas., 19, 307 - 308. Mayya YS, Eappen KP, and Nambi KSV (1998) Methodology for mixed field inhalation dosimetry in monazite areas using a twin-cup dosimeter with three track detectors, Rad. Prot. Dosimetry, 77, 177 - 184. Megumi K, and Mamuro T, (1974) Emanation and exhalation of radon and thoron gas from soil particles, J. of Geophys. Res., 79(23), 3357-3360. Menon, MR, Lalit, BY and Shukla, VK (1987) Natural radioactivity content in building construction materials in India, Bull. Rad. Prot, 14, 45 - 48. Mettler FA and Upton AC (1995) Medical Effects of Ionizing Radiation, 2nd edition, (Eds.) Saunders, W.B. Philadelphia. Miles JCH (1997) Calibration and standardization of etched track detectors, In Radon measurements by etched track detectors, applications in radiation protection, earth Sciences and the Environment (Eds, Durrani, S. A., and Ilic, R), World Scientific, Singapore, 143176. Mishra, UC and Sadasivan, S (1971) Natural radioactivity levels in Indian soil, J. of Sci.and Industrial Research, 30, 59 - 62. Nambi KSV, Bapat VN, David M, Sundaram VK, Sunta CM, and Soman SD (1986) Natural Background Radiation and Population Dose Distribution in India, BARC Report, Health Physics Division, Bhabha Atomic Research Center, Government of India, Mumbai. Nambi KSV, Subba Ramu MC, Eappen KP, Ramachandran TV, Muraleedharan TS, and Shaikh AN, (1994) A new SSNTD method for the measurement of radon-thoron mixed working levels in dwellings, Bull. of Rad. Prot., 17, 34 - 35. 18 Nazaroff WW (1988) Radon and its decay products in indoor air; (Eds. W. W. Nazaroff and A. V. Nero), Chapter 2, John Wiley & Sons, New York, pp. 57 - 112. Nero AV, Berk JV, Boegel CD, Hollowell JR, Ingersoll, and Nazaroff WW (1983) Radon concentrations and infiltration rates measured in conventional and energy efficient houses, Health Phys, 45,401 - 405. Nikolaeve VA and Ilic R (1999) Etched track radiometers in radon measurements: A review, Rad Meas., 30, 1-13. Planinic J and Faj Z (1990) Equilibrium factor and dosimetry of radon with a passive nuclear track etch detector, Rad. Prot. Dosimetry, 1, 97 - 109. Planinic J and Faj Z (1991) Dosimetry of radon and its daughters by two SSNTD detectors, Rad. Prot. Dosimetry, 35, 265 - 268. Porstendorfer J (1994) Properties and behavior of radon and thoron and their decay products in the air, J. Aerosol Sci, 25, 219 - 263. Porstendorfer J and Mercer TT (1979) Influence of electric charge and humidity up on the diffusion coefficient of radon decay products, Health Phys, 37, 191. Ramachandran TV, Eappen KP, Shaikh AN, and Mayya YS (2001) Indoor radon levels and equilibrium factors in Indian dwellings, Rad. Prot. and Envir, 420-422. Ramachandran TV, Subba Ramu MC, and Nambi KSV (1995) Simultaneous measurements of radon and its progeny using SSNTDs and evaluation of internal doses due to inhalation, Bull. Rad. Prot., 18, 109 - 114. Sadasivan S, Shukla VK, Chinnasaki S and Sartandel S J (2003) Natural and fallout radioactivity measurements in Indian soil, J. Radio, Anal. And Nucl. Chem., 256, 603 - 607. Sankaran AV, Jayswal V, Nambi K S V, and Sunta C M (1986) U,Th and K distributions inferred from region of geology and the terrestrial radiation profiles in India, Bhabha Atomic Research Center (Government of India) Report Shaikh AN, Muraleedharan TS, Ramachandran TV and Subba Ramu MC (1992) Estimation of ventilation rates in dwellings, The Sci. of the Tot. Envir, 121, 67 - 76. Sohrabi M (1997) High radon levels in nature and in Dwellings: Remedial actions, In Radon Measurements by Etched Track Detectors, Applications in Radiation Protection, Earth Sciences and the Environment, (Eds. Durrani, S.A., and Ilic, R), World Scientific, Singapore, 225 - 242. Steinhausler F, Hoffman W, and Lettner H (1994) Thoron exposure to man: A negligible issue? Rad. Prot. Dosi., 56, 1 - 44. Stranden E, Kolstad AK, and Lind B, (1984) The influence of moisture and Temperature and radon exhalation, Rad. Prot. Dosi., 7, 55-58. 19 Strong KP, and Levins DM, (1982) Effect of moisture content on radon emanation from uranium ore and tailing, Health Phys, 42, 27. Subba Ramu MC, Muraleedharan TS, and Ramachandran TV (1988) Assessment of lung dose from radon daughters in dwellings, Rad. Prot. Dosim., 22,187 - 191. Subba Ramu MC, Raghavayya M, and Paul AC, (1994) Methods for the measurement of radon, thoron and their progeny in dwellings, AERB Technical Manual, TM/RM - 1. Subba Ramu MC, Ramachandran TV, Muraleedharan TS, Shaikh AN, and Nambi KSV, (1993) Proc. of 7th.Nat. Conf. on Particle Tracks in Solids, Defense Laboratory, Jodhpur, 11 -25. Tanner AB (1980) Radon migration in the ground: A supplementary review, In proceeding of Natural Radiation Environment III (Eds., Gassel, T. F., and Lowder, W.M), Tech. Infor. Centre, US Department of Energy, Washington, D.C, CONF - 780422. United Nations Scientific Committee on the Effects of Atomic Radiation (1988) Sources, Effects and Risks of Ionizing Radiation, Report to the General Assembly, United Nations, New York. United Nations Scientific Committee on the Effect of Atomic Radiation (1992) Sources and Biological Effects, Report to the General Assembly., United Nations, New York. United Nations Scientific Committee on the Effects of Atomic Radiation (1993) Sources, Effects and Risks of Ionizing Radiation, Report to the GeneralAssembly, United Nations, New York. United Nations Scientific Committee on the Effect of Atomic Radiation (2000) Sources, Effects and Risks of Ionizing Radiation, Report to the General Assembly, United Nations, New York. Wafaa A (2002) Permeability of radon-222 through some materials, Rad. Meas., 35, 207 - 211 Ward WJ, Fleischer RL, and Mogro-Campero A (1977) Barrier technique for separate measurement of radon isotopes, Rev. Sci. Instr., 48, 1440 - 1441. Yihe J, Shimo M, Weihai Z, Liya Xu, and Guoqiu fang (1996) The size distribution of atmospheric radioactive aerosols and its measurement, Proc, of: 4th Int. Conf, on High Levels of Natural Radiation, Beijing, China, October, 21 - 25 (Eds., Luxin, Wei., Tsdtomu, Sugahara., and Zufan, Tao), Elseveir, Amsterdam, 1997, 97 - 109. 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