Indian Journal of Pure & Applied Physics Vol. 48, July 2010, pp. 470-472
Monitoring of radon, thoron and their progeny in dwellings of Haryana R P Chauhan Department of Physics, National Institute of Technology, Kurukshetra 136 119 E-mail:
[email protected];
[email protected] Received 22 April 2010; accepted 28 May 2010 The environmental monitoring of radon, thoron and their progeny in different dwellings of Northern Haryana has been carried out. The radon-thoron twin dosimeter cups are used for the study. The annual dose received due to radon-thoron and their progeny by the inhabitants in the dwellings under study have also been calculated. The health risk assessment in the dwellings under consideration has been done. Keywords: Radon, Thoron, Dwellings, Annual effective dose
1 Introduction About 90% of radiation exposure to human arises from natural sources such as cosmic radiation, terrestrial radiation and exposure to radon, thoron and their progeny. Studies have been made on exposure to many of the forms of natural radiations1. These studies have shown that more than 50% of annual exposure to humans is from radon and its daughter products. Also it is well-known that the radiations from the naturally occurring radioactive materials originating from the earth’s crust are the major contributors of total background exposures to the human populations which includes external gamma radiations and inhalation exposures, the latter being due to radon, thoron and their progeny2. The major inhalation dose is contributed by the radon progeny nuclides. A country wide survey of gamma exposure was carried out by Nambi et al.3 enabling them to prepare gamma exposure map of India. A similar profile of the terrestrial radioactivity was generated by Sankarn et al4. All building materials show various amounts of radioactivity as most of these are derived from rocks and soil which contain uranium-238 and thorium-232 series and the radioactive isotope of potassium-40. All these can be sources of both internal and external radiation exposure. Internal exposure takes place through the inhalation of radon gas and external exposure occurs through the emission of penetrating gamma radiations5. The problem of radon is an important global problem of radiation hygiene particularly in homes. Radon is a radioactive gas of natural origin and is produced by the disintegration of uranium. Radon mainly comes from grantic and volcanic subsoil as
well from certain construction materials. In general, there are three main mechanisms of radon entry into a building6; convection via utility access points, cracks and openings, diffusion from soil via the pore space of the building material and emanation from building materials. High radon concentration indoors is usually due to penetration from the surrounding soil. Radon levels in a home can fluctuate from day to day, depending upon the level of radon in the soil, type of soil, airflow through the soil, openings to buildings and ventilation. Underground water may also be contaminated with radon gas, which is released during showers and other household uses. Outdoor radon concentrations are low but indoors this gas may accumulate in high concentrations emitted from the soil and from building materials when the room is not properly ventilated. Radon emanation from the soil not only depends upon its radium content but also upon mineralogy, porosity, grain size, moisture content and permeability of host rock and soil6-7. Radon gas decays overtime into radioactive particles that can be inhaled and trapped in the lungs as these daughter products remain air borne for a long time. When radon decays it forms its progeny 218Po and 214Po, which are electrically charged and can attach themselves to tiny dust particles, water vapours, oxygen, trace gases in indoor air and other solid surfaces. These daughter products remain airborne for a long time and can easily be inhaled into the lung and can adhere to the epithelial lining of the lung, thereby irradiating the tissue. Bronchial stem cells and secretion cells in airways are considered to be the main target cells for the induction of lung cancer resulting from radon exposure. The exposure
CHAUHAN: RADON, THORON AND THEIR PROGENY IN HARYANA DWELLINGS
of population to high concentrations of radon and its daughters for a long period lead to pathological effects like the respiratory functional changes and the occurrence of lung cancer8. Based upon current knowledge about health effects of inhaled radon and its progeny, ICRP has made recommendations for the control of this exposure in dwellings and work place9. Keeping this in mind the environmental monitoring of radon, thoron and their progeny in some dwellings of northern Haryana has been carried out using radonthoron dosimeter cups. 2 Experimental Details For the measurement of radon and its progeny concentration radon-thoron twin dosimeter cups were used. The radon-thoron dosimeter cup has three different modes namely bare mode, filter mode and membrane mode. Three pieces (1 cm × 1 cm) of LR-115 solid-state nuclear track detectors were fixed in the dosimeters and were suspended in the dwellings for three months. The bare mode detector registers tracks due to radon, thoron and their progeny, the filter mode detector registers tracks due to radon and thoron while the membrane mode detector registers tracks only due to radon. The dosimeters were suspended at a height of about 1.5 m in order to evaluate the annual average indoor radon levels. At the end of the exposure time, the detectors were removed and subjected to a chemical etching process in 2.5N NaOH solution at 60°C for 90 min. The detectors were washed and dried and the tracks produced by the alpha particles were observed and counted under an optical Olympus microscope at 600X. A large number of graticular fields of the detectors were scanned to reduce statistical errors.
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The measured track density (track/cm2/d) was converted into radon and thoron concentration using calibration factors2. Radon and thoron progeny levels in mWL have also been calculated using indoor equilibrium factor 0.4 for radon and 0.1 for thoron from UNSCEAR10. Annual dose received by the inhabitants in the dwellings under study in mSv was estimated using the relation11-12: D = [(0.17 + 9FR)CR +(0.11+32FT)CT]×7000×10−6 where, FR =equilibrium factor for radon; CR = radon concentration; FT = equilibrium factor for thoron and CT = thoron concentration. 3 Results and Discussion The radon concentration in Northern region of Haryana varied from 66 ± 6 to 104 ± 12 Bq m−3 while the thoron concentration in the same dwellings varied from 27 ± 5 to 69 ± 10 Bq m−3. The radon progeny levels in the dwellings under study varied from 7.1 to 11.2 mWL while the thoron progeny levels varied from 0.7 to 1.8 mWL. Annual dose received by the inhabitants in the dwellings under study varied from 2.2 to 4.3 mSv (Table 1). The levels of radon, thoron and its progeny are higher in the districts of Panchkula and Yamunanagar as compare to Ambala and Kurukshetra due to their locations adjacent to the Shivalik hills of Himalayas. It may be due to the higher uranium contents in the soil of hilly area. In similar studies the radon levels in dwellings of neighbouring states are reported between 37 to 373 Bq m−3 (Table 2). The all India levels17 are between 40 to 143 Bq m−3 (Table 2).
Table 1 — Radon, thoron and their progeny levels in some dwellings of Haryana during summer season Location
Ambala PanchKula Yamunanagar Kurukshetra Ladwa Sahabad Naryangarh Radur Kaithal
No. of dwellings
8 8 10 12 10 8 6 8 10
Radon concentration (Bq m−3) AM ± SE*
Thoron concentration (Bq m−3) AM ± SE*
92 ± 6 104 ± 12 97 ± 11 66 ± 6 83 ± 7 88 ± 7 95 ± 9 73 ± 5 81± 12
64± 7 69± 10 65± 6 27± 5 52 ± 9 55 ± 8 67 ± 7 35± 4 48± 9
Progeny levels (mWL) Radon
Thoron
Annual Dose received (mSv)
9.9 11.2 10.5 7.1 9.0 9.5 10.3 7.9 8.7
1.7 1.8 1.8 0.7 1.4 1.5 1.8 1.0 1.3
3.9 4.3 4.1 2.2 3.4 3.6 4.1 2.7 3.3
*SE (standard error) = σ/√ N, Where σ is SD (standard deviation) and N is the no of observations
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Table 2 — Comparison of indoor radon levels with some other studies of the Area Values from literature (Bq m−3)
Region
Reference
58-240 37-134 145-165 42-168 30-287 44-373 13.5-143 66-104
Punjab Rajasthan Himachal Pradesh Palampur (H.P.) Tamilnadu Kerala All India Northern Haryana
13
Singh et al., 2005 Kumar et al., 1994 15 Virk, 1999 16 Kumar et al., 2003 17 Kumar & Prasad, 2007 19 Kumar et al., 2007 17 Ramchandran, 1998 Present study 14
The measurements indicate normal levels of radon concentration in the cemented dwellings of Northern part of Haryana State of India. The radon levels are within ICRP limits of 200 Bq m−3 for dwellings9. Acknowledgement The co-operation from house owners in different towns during present study is thankfully acknowledged. References 1 Mcaulay I R & Mclaughlin J P, Sci Total Environ, 45 (1985) 319. 2 Eappen K P & Mayya Y S, Radiat Measurem, 38 (2004) 5. 3 Nambi K S V, Bapat V N, David M, Sundran V K, Sunta C M & Soman S D, Natural background radiation and population dose distribution in India, Health Physics Division, BARC, 1986.
4 Sankaran A V, Jayaswal B, Nambi K S V & Sunta C M, Technical Report on the terrestrial radiation profiles in India, BARC, 1986. 5 Lee E M, Menezes G & Finch E C, Health Phys, 86 (2004) 378. 6 Ball T K, Cameron D G, Colman T B & Robert P D, Q J Eng Geology, 24 (1991) 169. 7 Grastly R L, Health Phys, 65 (1994) 185. 8 BEIR VI, Report of the Committee on the Biological effects of Ionizing Radiation, National. Research. Council (Natl Acad Press, Washington, DC), 1999. 9 ICRP, International Commission on Radiological Protection, publication No 65, in Annals of ICRP (Oxford Pergamon Press), 1993. 10 UNSCEAR (United Nations Scientific Committee on the Effects of Atomic Radiation), Exposures from Natural Sources of Radiation, A/Ac., 82/R, 1992, p 511. 11 Sannappa J, Chandra Shekara M S, Sathish L A, Paramesh L & Venkataramaiah P, Radiat Measurem, 37 (2003) 55. 12 Mayya Y S, Eappen K P & Nambi K S V, Radiat Prot Dosim, 77 (1998) 177. 13 Singh S, Mehra R & Singh K, Environ Geochem, 8 (2005) 166. 14 Kumar S, Gopalani D & Jodha A S, Bull of Radiat Protect, 17 (1994) 41. 15 Virk H S, Environ Int, 25 (1999) 47. 16 Kumar R, Mahur A K, Varshney A K & Parsad R, Indian J Pure & Appl Phys, 23 (2003) 1098. 17 Kumar R & Prasad R, Indian J Pure & Appl Phys, 45 (2007) 119. 18 Kumar R, Mahur A K, Jojo P & Prasad R, Indian J Pure & Appl Phys, 45 (2007) 880. 19 Ramchandran T V, In the Proc of 11th Natl Symp on SSNTDs-98, Department of Physics, GND University Amritsar, 1998, p 58.
