indoor radon measurements in the dwellings of ...

Radiation Protection Dosimetry Advance Access published March 17, 2013 Radiation Protection Dosimetry (2013), pp. 1–7

doi:10.1093/rpd/nct041

INDOOR RADON MEASUREMENTS IN THE DWELLINGS OF PUNJAB AND HIMACHAL PRADESH, INDIA Asha Rani1,*, Surinder Singh2 and Vikas Duggal3 1 Department of Applied Sciences, Ferozpur College of Engineering and Technology, Ferozshah, Ferozpur 142052, India 2 Department of Physics, Guru Nanak Dev University, Amritsar 143005, India 3 Department of Applied Sciences, Punjab Technical University, Jalandhar 144001, India *Corresponding author: [email protected] Received August 12 2012, revised January 21 2013, accepted February 24 2013

INTRODUCTION Radon is a naturally occurring odorless, colorless, tasteless inert gas which is imperceptible to our sense. It is produced continuously from the decay of naturally occurring radionuclides such as 238U, 235U, 232 Th. The isotope 222Rn, produced from the decay of 238U, is the main source (55 %) of internal radiation exposure to human life(1). The worldwide average AED from ionizing radiation from natural sources is estimated to be 2.4 mSv, of which 1.0 mSv is due to radon exposure(2). Radon isotopes can isolate themselves and migrate away from the parent mineral due to diffusion process through the soil and enter the atmosphere. The radon and its progeny attached to aerosols present in the ambient air constitute significant radioactive hazards to human lungs. During respiration radon progeny deposits in the lungs and irradiate the tissue thereby damaging the cells and may cause lung cancer and is the second leading cause of lung cancer deaths(3). In addition to this Henshaw et al.(4) also claimed that indoor radon exposure is associated with the risk of leukaemia and certain other cancers, such as melanoma and cancers of the kidney and prostate. The concentration of radon and its decay products show large temporal and local fluctuations in the indoor atmosphere due to the variations in temperature, pressure, nature of building materials, ventilation conditions and wind speed, etc. Radon gas in the air is present worldwide, its concentration

depending on the highly variable uranium content of the soil. The exposure due to inhalation of radon and its daughters is highest of the natural radionuclides to which human beings in the general environment are exposed. On the basis of the epidemiological studies it has been established that the enhanced levels of indoor radon in dwellings can cause health hazards and may lead to serious diseases like lung cancer in human beings(5 – 7). Radon generates the main natural radiation exposure for human beings and has been recognized as a carcinogenic gas(8). In the study area 18 villages and 5 houses in each village were chosen for indoor radon studies. The houses were chosen in such a way that the dwellings constructed with different types of building materials and in different localities of the village are covered. Geology of the area Figure 1 shows the geographic location of the states of Punjab and Himachal Pradesh in the map of India, as well as the location of the sampling sites. The geographic location of the study area in Punjab (Amritsar to Pathankot) is between latitudes 31.37 and 32.17 N and between longitudes 74.55 and 75.42 E. Punjab sediments are derived from Siwalik Himalayas and occur in the form of alluvium. The study area in Himachal Pradesh which falls in the Kangra district lies between 32.05 and 32.29 N latitude and between 75.10 and 76.18 E longitudes. The Kangra district is bounded on the South West by the

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The measurement of indoor radon concentrations were performed in the dwellings of the Punjab and Himachal Pradesh, India by using LR-115 type II Solid-State Nuclear Track Detectors in the bare mode. The annual average indoor radon concentrations in the dwellings are found to vary from 114 to 400 Bq m23 with an average of 194 Bq m23. In ∼22 % of the dwellings the indoor radon activity concentration values lies in the range of action level (200–300 Bq m23) and in ∼11 % of the dwellings above the upper limit of action level recommended by the International Commission on Radiological Protection (ICRP). The annual effective dose (AED) varies from 2.88 to 10.08 mSv with an average of 4.88 mSv. In most of the villages, the AED lies in the range of action level (3– 10 mSv) recommended by the ICRP. The seasonal variation in indoor radon reveals the maximum values in winter and minimum in summer. The winter/summer ratio of indoor radon ranges from 1.15 to 1.62 with an average of 1.31. Analysis of ventilation conditions reveal that the indoor radon concentration values are more in poorly ventilated dwellings compared with the well-ventilated ones.

RANI ET AL.

Una district; on the North West by district Gurdaspur of Punjab, on the North by Lahaul-Spiti and Chamba districts, on the East by Kullu and Mandi districts, while on South it touches Hamirpur district. The area is characterized by the occurrence of following formations/Groups from north to south viz. Dhauladhar granites, Chail formation, Dharamshala traps, Dharamkot limestone, Sabathus, Dharamshala Group and Shivalik Group. The individual formation and groups are separated from one another by longitudinal thrust systems; significant among them are Main Boundary Thrust, Chail Thrust and the Drini Thrust. Apart from these tectonic planes, the rock units are cross cut by transverse faults/lineaments trending NE–SW. The southern extremity and parallel to the lesser Himalayas is the Shivalik group of rocks, which are succeeded by vast stretch of Quaternary alluvium of the state of Punjab. Rock type comprises both palaeogene and neogene sediments. However, Precambrian Sundernagar formation along with the Mandi Darla trap occurs at close proximity to the Mandi town. Palaeogene –Neogene contact is

marked by MBT (Main Boundary Thrust). The dominant rock type is the Mandi granite which is even visible along the road section (Mandi-Kullu Highway). Shimla is a tectonic outlier where younger rocks are exposed due to the erosion of the older ones. It is bounded by the MBT in the south and main central thrust (MCT) in the north. In nutshell, the two important thrust systems MBT and MCT passes through the south central territory of Himachal Pradesh state. The two thrusts come in close vicinity to each other near Dharamsala and other areas of Himachal Pradesh. This explains the tectonic significance of Kangra-Dharamsala region in particular and lower Himalayan region of Himachal Pradesh in general. MATERIALS AND METHODS Several methods are in use for the measurement of radon and its daughter elements in dwellings. Some measuring the short-term values are called active methods and others measuring the integrated values are called passive methods. LR-115 type II plastic

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Figure 1. Map of Punjab and Himachal Pradesh showing the surveyed area during the present investigations.

RADON MEASUREMENTS IN THE DWELLINGS OF INDIA

progeny is calculated using the following equation (UNSCEAR, 2000)(2). AED ¼ A 0:4 0:8 8760 ð9 106 mSv=Bq m3 hÞ

ð1Þ

where A is the radon concentration (Bq m23), 0.4 is an equilibrium factor, 0.8 is an occupancy factor, 8760 hy21 is hours in a year and 9 10 – 6 mSv/Bq m23 h is the dose conversion factor. RESULTS AND DISCUSSION The results for the average annual indoor radon concentration recorded in 18 villages of Punjab and Himachal Pradesh, India are given in Table 1. The annual average indoor radon concentrations in the dwellings are found to vary from 114 to 400 Bq m23 with an average of 194 Bq m23. In 22 % of the dwellings the indoor radon activity concentration values lies in the range of action level (200–300 Bq m23) and in 11 % of the dwellings above the upper limit of action level recommended by the International Commission on Radiological Protection (ICRP)(13). The annual average indoor radon concentration values obtained in the present investigation

Table 1. Seasonal variation in the indoor radon activity concentration and AEDs. Sr. no

Sample location

Punjab 1 Amritsar 2 Batala 3 Dhariwal 4 Gurdaspur 5 Dinanagar 6 Pathankot Himachal Pradesh 7 Jaisur 8 Nurpur 9 Kotla 10 Gaggal 11 Dharamsala 12 Upper Skoh 13 Kangra 14 Nagri 15 Nagrota 16 Bandla village 17 Palampur 18 Shimla Total

Detector no.

Radon concentration (Bq m – 3) in winter (October– March)

Radon concentration (Bq m23) in summer (April–September) Max. Min.

Annual average radon concentration (Bq m23)

AED (mSv)

Max. Min.

Average value+SD

1 –5 6 –10 11–15 16–20 21–25 26–30

208 305 181 160 139 164

174 262 139 133 120 141

191+11.98 284+16.07 159+14.08 146+9.44 128+6.99 152+8.12

166 247 137 121 112 131

145 189 85 104 89 114

154+7.44 216+18.81 106+19.61 113+6.62 100+8.69 123+5.89

173 250 133 130 114 138

4.35 6.31 3.34 3.27 2.88 3.47

31–35 36–40 41–45 46–50 51–55 56–60 61–65 66–70 71–75 76–80

164 453 243 164 152 453 239 195 361 212

133 382 214 139 125 409 172 160 307 185

145+11.18 416+26.50 228+10.67 150+8.45 139+9.64 428+15.41 199+23.53 177+12.92 329+19.19 198+10.46

127 363 197 127 116 390 208 152 276 135

98 332 172 104 94 347 137 93 249 110

113+9.72 347+11.50 183+8.77 115+7.94 104+7.74 371+15.38 175+25.26 124+22.53 266+9.85 123+9.31

129 382 206 133 122 400 188 151 298 161

3.25 9.62 5.18 3.34 3.06 10.08 4.72 3.80 7.51 4.05

81–85 86–90 90

231 255 453

166 208 120

201+22.62 231+15.99 216.72

175 199 390

118 160 85

155+20.38 179+14.35 170.39

178 205 194

4.49 5.17 4.88

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Average value+SD


track detector films and the bare mode technique have been employed to measure the concentration of radon in the indoor environment (9 – 11). The detectors of size 1.5 cm 1.5 cm were suspended in the rooms of the dwellings at a height .2 m above the ground level (so that the detectors were not disturbed by the movement of the residents) and 1 m below the ceiling of the room so that direct alpha particles from the building material of the ceiling did not reach the detectors. The authors have assumed that a room with a door and without window is poorly ventilated, that with one window and a door as partially ventilated and with two or more windows and a door as well ventilated. After exposure the detectors were removed and etched using 2.5-N NaOH solutions at 608C for 90 min. After through washing, the detectors were scanned for track density measurements using the Carl Zeiss optical microscope at a magnification of 400 . The track density so obtained was converted into the units of Bq m23 of the radon concentration using the calibration factor of 0.020+0.002 tracks cm22 d21 (Bq m23)21 determined experimentally by Eappen et al.(12), which satisfies the conditions prevailing in the Indian dwellings. According to the UNSCEAR report, the AED (mSv y21) to the public from radon (222Rn) and its

RANI ET AL.

ventilation is well and radon concentrations in the summer were lower than the other seasons. In winter season, generally, the doors and windows of the dwellings remain closed. Because of this reason, the ventilation is poor and radon concentrations in the winter were higher than the other seasons. It is evident from Table 2 that the radon level in poorly ventilated houses is more compared with that in the well-ventilated houses. This is because in well-ventilated dwellings the radon can easily escape out and hence does not accumulate inside so that the radon level inside becomes lower in well-ventilated houses in comparison with poorly ventilated houses. Thus, the ventilation conditions are found to affect radon concentration in dwellings. The winter-to-summer ratio of indoor radon obtained in the present investigations in the studied areas are also compared with the different regions of India (Table 3). The winter-to-summer ratio of indoor radon in Muktsar and Ferozepur districts of Punjab lies in the range of 0.9 to 1.8 with an average value of 1.4 as reported by Singh et al.(14). Singh et al.(15) has reported winter-to-summer ratio of indoor radon in the Malwa region of Punjab in the range of 0.84–1.89 with an average value of 1.46. Kansal et al.(16) has reported winter-to-summer ratio of indoor radon in the range of 0.78–2.99 with an average value of 1.52 in the Western Haryana, India. The winter-to-summer ratio of indoor radon in Kullu area of Himachal Pradesh, India lies in the range of 1.08 to 1.96 with an average value of 1.54 as reported by Singh et al.(11). Kandari et al.(17) has reported winter-to-summer ratio of indoor radon in range of 0.63 to 1.64 with an average value of 1.16 in the Tehri Garhwal region of Northern India. The winterto-summer ratio of indoor radon in Hoshiarpur

Figure 2. Frequency distribution of annual average radon concentration among various dwellings.

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are higher than the world average of 40 Bq m23(2). This may be due to the difference in the concentration of radioactive elements viz. uranium and radium in the soil and building materials of the study area. The AED varies from 2.88 to 10.08 mSv with an average of 4.88 mSv. From Table 1, it is evident that in most of the villages, the AED lies in the range of suggested action level (3–10 mSv)(1). These values are higher than the world average AED of 1.2 mSv given by United Nations Scientific Committee on the effects of Atomic Radiation(2). Figure 2 shows the frequency distribution of the annual average radon concentration among 90 dwellings of 18 villages of the study area. The radon concentration lies in the ranges of 100–150, 150–200, 200–250, 250–300, 300–350, 350–400 and 400–450 Bq m23 in 43.33, 24.44, 13.33, 5.55, 2.22, 6.66 and 4.44 % of the houses, respectively. The difference in the values of indoor radon activity concentration may be due to the different ventilation conditions, type of building materials used during construction and the variation in the radioactivity level in the soil beneath the dwellings. The ventilation conditions and winter/summer ratio of the radon activity concentration has been computed for all the dwellings (Table 2). The winter/summer ratio of indoor radon ranges from 1.15 in village Upper Skoh to 1.62 in village Bandla village with an average of 1.31. From Table 1 it has been observed that there is a considerable variation in the indoor radon concentration levels with the seasons during the complete year. From Table 2 and Figure 3, it is evident that the average indoor radon concentration level is minimum during the summer season and maximum during the winter season. In summer season, generally, the fans are used and all windows are kept open. Because of this reason, the

Table 2. The ventilation conditions and winter/summer ratio of the radon activity concentration for all the dwellings.

Amritsar

Radon concentration (Bq m23) in dwelling 1





Average winter/ summer ratio Ventilation Winter Summer Winter/ Ventilation Winter Summer Winter/ Ventilation Winter Summer Winter/ Ventilation Winter Summer Winter/ Ventilation Winter Summer Winter/ condition summer condition summer condition summer condition summer condition summer ratio ratio ratio ratio ratio

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Poorly ventilated 2 Batala Poorly ventilated 3 Dhariwal Partially ventilated 4 Gurdaspur well ventilated 5 Dinanagar Partially ventilated 6 Pathankot Partially ventilated 7 Jaisur Partially ventilated 8 Nurpur Poorly ventilated 9 Kotla Poorly ventilated 10 Gaggal Partially ventilated 11 Dharamsala well ventilated 12 Upper Skoh Poorly ventilated 13 Kangra well ventilated 14 Nagri Partially ventilated 15 Nagrota Poorly ventilated 16 Bandla Poorly village ventilated 17 Palampur Partially ventilated 18 Shimla Poorly ventilated

208

166

1.25

305

247

1.23

181

137

1.32

160

120

1.33

139

108

1.29

164

131

1.25

164

127

1.29

453

363

1.25

243

197

1.23

164

127

1.29

152

116

1.31

453

390

1.16

239

185

1.29

195

152

1.28

361

276

1.31

185

125

1.48

231

175

1.32

255

199

1.28

Poorly ventilated Poorly ventilated Partially ventilated well ventilated Partially ventilated Partially ventilated well ventilated Partially ventilated Partially ventilated well ventilated well ventilated Poorly ventilated Partially ventilated well ventilated Partially ventilated Poorly ventilated Partially ventilated Poorly ventilated

201

158

1.27

262

189

1.39

164

62

1.37

133

104

1.28

133

112

1.19

141

114

1.24

133

98

1.36

440

357

1.23

218

176

1.24

150

120

1.25

147

108

1.36

424

376

1.13

172

189

0.91

166

93

1.78

307

249

1.23

212

129

1.64

189

152

1.24

237

191

1.24

Partially ventilated Partially ventilated Poorly ventilated Partially ventilated Poorly ventilated well ventilated well ventilated Poorly ventilated well ventilated Partially ventilated well ventilated Poorly ventilated well ventilated well ventilated Partially ventilated Partially ventilated Poorly ventilated Partially ventilated

185

154

1.20

285

208

1.37

139

85

1.63

150

114

1.31

120

89

1.35

150

125

1.20

139

108

1.29

397

338

1.17

228

181

1.26

145

110

1.32

125

98

1.27

409

361

1.13

208

156

1.33

177

108

1.64

339

262

1.29

197

135

1.46

201

158

1.70

208

168

1.24

Partially ventilated Partially ventilated Partially ventilated well ventilated Poorly ventilated Partially ventilated Partially ventilated Poorly ventilated Partially ventilated Partially ventilated Poorly ventilated Poorly ventilated well ventilated well ventilated Partially ventilated Partially ventilated well ventilated Partially ventilated

189

148

1.28

270

220

1.23

150

89

1.68

139

108

1.29

125

100

1.25

147

120

1.22

152

118

1.29

409

347

1.18

235

187

1.26

154

116

1.33

133

94

1.41

436

382

1.14

193

208

0.93

160

121

1.32

314

274

1.14

208

114

1.82

166

118

1.41

220

160

1.37

well ventilated Partially ventilated well ventilated well ventilated Partially ventilated Poorly ventilated well ventilated Poorly ventilated Partially ventilated well ventilated well ventilated Partially ventilated well ventilated Partially ventilated Poorly ventilated Poorly ventilated well ventilated Partially ventilated

174

145

1.20

1.24

297

216

1.37

1.32

160

100

1.60

1.52

150

121

1.24

1.29

123

93

1.32

1.28

158

127

1.24

1.23

139

114

1.22

1.29

382

332

1.15

1.20

214

172

1.24

1.25

139

104

1.34

1.31

139

102

1.36

1.34

417

347

1.20

1.15

181

137

1.32

1.16

‘187

147

1.27

1.46

326

270

1.21

1.24

189

110

1.72

1.62

218

172

1.27

1.39

235

177

1.33

1.29


1

Sample location


Sr. no

RANI ET AL.

Table 3. Comparison of winter-to-summer ratio of indoor radon in the different regions of India. Sr. No

1 2 3 4 5 6 7

Region

Winter/summer ratio

Muktsar, Ferozepur district, Punjab Malwa region, Punjab Western Haryana, India Kullu area, Himachal Pradesh Tehri Garhwal, Northern India Hoshiarpur district, Punjab Punjab and Himachal Pradesh, India

district of Punjab lies in the range of 0.83 to 3.14 as reported by Badhan et al.(18). The winter-to-summer ratio of indoor radon values in the present investigations lies within the range reported by other investigators. The indoor radon values obtained in the present investigations are comparatively lower than those reported in some dwellings of Hamirpur (660–1060 Bq m23, (19)), Kullu (156–635 Bq m23,(11)) and Una (235–970 Bq m23,(20)) districts of Himachal Pradesh. The higher indoor radon values in these areas are explained due to the presence of uranium mineralization in the area(21).

CONCLUSIONS The annual average indoor radon concentration values vary from 114 to 400 Bq m23 with an average value of 194 Bq m23. In 22 % of the dwellings the indoor radon activity concentration values lie in the range of action level (200–300 Bq m23) and in 11 % of the dwellings above the upper limit of

Range

Average

0.9–1.8 0.84–1.89 0.78–2.99 1.08–1.96 0.63–1.64 0.83–3.14 1.15–1.62

1.4 1.46 1.52 1.54 1.16 — 1.31

Reference

Singh et al.(14) Singh et al.(14) Kansal et al.(16) Singh et al.(11) Kandari et al.(17) Mehra et al., 2012 Present investigation

action level recommended by the ICRP(13). The average winter/summer ratio of radon activity concentrations was 1.31. Maximum values of the radon concentration are observed during the winter and minimum during the summer season. Analysis of ventilation conditions reveal that the indoor radon concentration values are more in poorly ventilated dwellings compared with the well-ventilated ones. Thus, the ventilated conditions play a dominant role in the indoor radon environment. The average value for the AED was found to be 4.88 mSv, which lies in the range of suggested action level (3–10 mSv)(1). The higher indoor radon values in the study areas are explained due to the presence of uranium mineralization in the area.

ACKNOWLEDGEMENTS The authors are thankful to the residents of the study area for their cooperation during the fieldwork, and Department of Physics, Guru Nanak Dev

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Figure 3. Variation in the winter/summer ratio with sample location.


University, Amritsar for providing experimental facilities.

11.

REFERENCES 12.

13. 14.

15. 16.

17.

18.

19.

20.

21.

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1. International Commission on Radiological Protection, and (ICRP). Protection against Radon-222 at home and at work. ICRP Publication 65. Ann. ICRP 23(2) Pergamon Press (1993). 2. United Nation Scientific Committee on the Effects of Atomic Radiation Report. Sources and effects of ionizing radiation. Annex B: Exposure due to Natural Radiation Sources, Vol. 1 United Nation (2000). Available on www.unscear.org. 3. "Health Risks j Radon j U.S. EPA". U.S. Environmental Protection Agency. http://www.epa. gov/radon/healthrisks.html (accessed 14 September 2009). 4. Henshaw, D. L., Eatough, J. P. and Richardson, R. B. Radon as a causative factor in induction of myeloid leukaemia and other cancers. Lancet 355, 1008–1015 (1990). 5. Axelson, O. Cancer risks from exposure to radon in homes. Environ. Health Perspect. 103(2), 37– 43 (1995). 6. Bochicchio, F., Forastiere, F., Abeni, D. and Rapiti, E. Epidemiologic studies on lung cancer and residential exposure to radon in Italy and other countries. Radiat. Prot. Dosim. 78(1), 33–38 (1998). 7. Field, R. W., Steck, D. J., Smith, B. J., Brus, C. P., Neuberger, J. S., Fisher, E. F., Platz, C. E., Robinson, R. A., Woolson, R. F. and Lynch, C. F. Residential gas exposure and lung cancer: the lowa radon lung cancer study. Am. J. Epidemiol. 151 (11), 1091– 1102 (2000). 8. IARC (International Agency for Research on Cancer). Radon and man-made mineral fibres. Monographs on the evaluation of carcinogenic risks to humans, Vol. 43. IARC (1988). 9. Mishra, U. C. and Ramachandran, T. V. Indoor radon levels in India: a review. In: Proceedings Third International Conference on Rare Gas Geo-Chemistry, Amritsar. Guru Nanak Dev University Press, Amritsar, India, pp. 310– 319 (1997). 10. Ramola, R. C., Kandari, M. S., Rawat, R. B. S., Ramachandran, T. V. and Choubey, V. M. A study of

seasonal variation of radon levels in different types of houses. J Environ. Radioact. 39(1), 1– 7 (1998). Singh, S., Malhotra, R., Kumar, J. and Singh, L. Indoor radon measurements in dwellings of Kulu area, Himachal Pradesh, using solid state nuclear track detectors. Radiat. Meas. 34, 505–508 (2001). Eappen, K. P., Ramachandran, T. V., Shaikh, A. N. and Mayya, Y. S. Calibration factors for SSNTD based radon/thoron dosimeters. Radiat. Prot. Environ. 24(1 & 2), 410–414 (2001). ICRP. International Commission on radiological protection statement on radon. ICRP Ref. 00/902/09 (2009). Available on www.icrp.org. Singh, S., Mehra, R. and Singh, K. Study of seasonal variations for radon pollution in the environment of Muktsar and Ferozepur districts of Punjab using LR115 plastic track detectors. J. Environ. Sci. Eng.. 47(4), 286–289 (2005). Singh, S., Mehra, R. and Singh, K. Seasonal variation of indoor radon in dwellings of Malwa region, Punjab. Atomos. Environ. 39, 7761–7767 (2005). Kansal, S., Mehra, R. and Singh, N. P. Life time fatality risk assessment due to variation of indoor radon concentration in dwellings in Western Haryana, India. Appl. Radiat. Isot. 70, 1110–1112 (2012). Kandari, M. S. and Ramola, R. C. Analysis of seasonal variation of indoor radon concentration in Tehri Garhwal, Northern India. Indian J. Phys. 83(7), 1019–1023 (2009). Badhan, K., Mehra, R. and Sonkawade, R. G. Studying the variation of indoor radon levels in different dwellings in Hoshiarpur district of Punjab, India. Indoor Built Environ. 21(4), 601–606 (2012). Kumar, J., Malhotra, R., Singh, J. and Singh, S. Radon measurements in dwellings in radioactive areas in Himachal Pradesh, India, using LR-115, plastic track detectors. Nucl. Geophys. 8(6), 573– 576 (1994). Singh, S., Kumar, A. and Singh, B. Radon level in dwellings and its correlation with uranium and radium content in some areas of Himachal Pradesh, India. Environ. Int. 28, 97– 101 (2002). Kaul, R., Umamaheshwar, K., Chandrashekharan, S., Deshmukh, R. D. and Swarmukar, B. M. Uranium mineralization in the Siwaliks of North Western Himalayan, India. J. Geol. Soc. India. 41, 243–258 (1993).