Radiation Protection and Environment

ARTICLE
Year
: 2011  |  Volume : 34  |  Issue : 4  |  Page : 225--228

Study on airborne radioactivity levels in dwellings of Tumkur district, Karnataka state, India


A Jayasheelan1, J Sannappa2, K Umeshareddy3, C Ningappa4, S Manjunatha5,  
1 Department of Physics, Government First Grade College, Sira, Affiliated to Tumkur University, Karnataka, India
2 Jnana Sahyadri, Kuvempu University Shimoga, Karnataka, India
3 Government First Grade College for Women Hassan, Karnataka, India
4 Vidya Vikas Institute of Engineering and Technology Mysore, Karnataka, India
5 P.E.S Institute of Technology and Mangement, Shimoga, Karnataka, India

Correspondence Address:
S Manjunatha
P.E.S Institute of Technology and Mangement, Shimoga, Karnataka
India

Abstract

Radon is a radioactive gas produced by the decay of 226 Ra present in the soil, rock, water and in atmosphere. Radon, thoron and their progeny are present in indoor and outdoor atmosphere. The concentration of these gases in indoor atmosphere is higher than that of outdoor. In the present study, the concentrations of radon, thoron and their progenies in some taluks of Tumkur district were estimated and the doses due them were calculated. Twin cup dosimeters with alpha sensitive films, LR- 115 type-2, were used for the measurement of concentrations of radionuclides. The mean indoor gamma radiation dose was found to be 0.64 mSvy−1 with highest of 0.75 mSvy−1 in Kunigal taluk. The concentrations of radon in good ventilated dwellings with granite floorings varied from 20.66 Bqm−3 in Tumkur city to 27.61 Bqm−3 in Kunigal. In poor ventilated dwellings, the concentrations of radon varied from 35.56 Bqm−3 in Tumkur to 44.87 Bqm−3 in Turuvekere. The dwellings with granite flooring showed higher concentration of radioactive gases than with marble as flooring and other floorings. The dwelling situated near the granite rocks showed higher concentrations.



How to cite this article:
Jayasheelan A, Sannappa J, Umeshareddy K, Ningappa C, Manjunatha S. Study on airborne radioactivity levels in dwellings of Tumkur district, Karnataka state, India.Radiat Prot Environ 2011;34:225-228


How to cite this URL:
Jayasheelan A, Sannappa J, Umeshareddy K, Ningappa C, Manjunatha S. Study on airborne radioactivity levels in dwellings of Tumkur district, Karnataka state, India. Radiat Prot Environ [serial online] 2011 [cited 2021 Jul 30 ];34:225-228
Available from: https://www.rpe.org.in/text.asp?2011/34/4/225/106073


Full Text

 1. Introduction



Radon is a radioactive noble inert gas directly produced by the decay of 226 Radium, resulting itself from the radioactive decay of 235 U, 238 U, and 232 Th series present in the building materials. Prolonged exposure of radon and its daughters affects human respiratory organ and increases the chances of lung cancer. [1] UNSCEAR report indicates that there is a remarkable coherence between the risk estimates developed from epidemiological studies from miners and residential case-control radon studies. [2],[3] Though thoron concentrations in dwellings is considered negligible because of the short lifetime (55.6 s), but while calculating the risk, the concentration of thoron and its progeny can't be ignored. The radon gas produced from the building materials diffuse and emanate through the pore spaces. The materials used to construct the buildings are same in the study area, except the floorings. The floorings may be made up of cement, mosaic, marble granite etc., The ventilation condition also varies from one dwelling to another dwelling. Hence, the concentrations of radon, thoron and their progenies are measured in dwellings with different floorings and ventilation conditions. The present area of study is Tumkur District, which is located in southern India, with 13° 20 1 latitude and 77° 05 1 longitude.

 2. Materials and Methods



In the present study, poorly and well-ventilated similar (houses of area 30 1 × 40 1 ) type of dwellings with floors made up of cement, mosaic, marble and granite in few taluks of Tumkur district were chosen. In each taluk, Eight dwellings in each type of floorings were studied. The indoor ambient gamma radiation levels around the study area have been measured using Scintillometer (Type SM 141D). The gamma exposure rate in μR.h -1 was converted into absorbed dose rate using the conversion factor 1 μR.h -1 = 8.7 nGy h -1 . [4] The effective gamma dose is calculated using the conversion factor of 84 nGy h -1 = 0.41 mSvy -1 , with indoor occupancy factor of 0.8 1 . Solid State Nuclear Track Detector (SSNTD), LR-115 type-II, detectors were used in the twin cup dosimeters to measure the concentrations of radon, thoron and their progenies in different dwellings in the study area. The schematic diagram of twin cup dosimeter is shown in [Figure 1]. The dosimeters were deployed at a height of 2 m from the floor of the dwellings by suspending them from the roof using threads. The films were exposed for 90 days, developed; tracks produced were counted using a spark counter and converted into concentrations of radioactive gases using suitable formulae.{Figure 1}

 3. Formulae



3.1. The radon and thoron concentrations were determined using [5],[6],[7],[8]

[INLINE:1]

Where, C R and C T are the radon and thoron concentration, respectively. T m and T f are the track densities in membrane and filter mode, respectively.

Sensitivity factor of membrane compartment (S m ) = 0.0193 ± 0.003 Traccm -2 d -1 /Bqm -3

Sensitivity factor for radon in filter compartment (S rf ) = 0.020 ± 0.004 Traccm -2 d -1 /Bqm -3

Sensitivity factor for thoron in filter compartment (S tf ) = 0.016 ± 0.005 Traccm -2 d -1 /Bqm -3

3.2. The radon and thoron progeny concentrations are calculated using

[INLINE:2]

3.3. The annual inhalation dose in was estimated using [1]

[INLINE:3]

Where, C R and C T are concentration of radon and thoron, respectively, F R and F T are the equilibrium factors for radon and thoron, respectively, C and C are the radon and thoron progeny concentrations, respectively, 7000h is the indoor occupancy period (occupancy factor = 0.8).

 4. Results and Discussion



[Table 1] shows the variation of indoor ambient gamma level in different dwellings. The indoor effective doses were found to be highest in Kunigal with 0.75 mSvy -1 and lowest was found in Gubbi with 0.60 mSvy -1 . The increase in gamma radiation level in Kunigal region may be due to the presence of granites. Earlier studies in granitic areas of Bangalore rural area showed higher concentrations of radon, thoron and their progenies with 7.6 mSv annual effective dose. [9] The variation of radon concentration in different flooring materials depends on the radium content of the material. From [Table 1] and [Table 2], it is observed that the concentration of radon, thoron and their progenies were found to be highest in dwellings made up of granitic floorings in all the five taluks under study, and the lowest were observed in marble floorings in four regions.{Table 1}{Table 2}

Cement floorings are made up of mixture of limestone and gypsum and gravel which increases the radium content of the floor, hence radon exhalations are higher. Marble mainly contains silica and lower activity of radio nuclides compared to granites, hence radon concentration was found to less than that of dwellings with cement, mosaic, and granitic floorings. The ventilation of the dwellings also plays a vital role in the indoor radon concentrations. Poor ventilation leads to accumulation of radioactive gases in the dwelling, which leads to higher radon concentration and vice versa.

 5. Conclusion



The average inhalation dose due to radon and thoron in the Five taluks of Tumkur district was 0.638 mSvy -1 for good ventilated dwelling and 1.025 mSvy -1 for poorly-ventilated dwellings [Table 3]. The regions with granite geology showed elevated amount of radon concentrations. The dwellings made with marble flooring showed low concentration of radon and with granite flooring showed higher radon concentration.{Table 3}

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