|Year : 2014 | Volume
| Issue : 3 | Page : 157-160
Determination of radon, thoron and their progeny concentrations in dwellings of Gogi region, Yadgir District, Karnataka, India
PR Avinash1, S Rajesh1, BR Kerur1, Rosaline Mishra2
1 Department of Physics, Gulbarga University, Gulbarga, Karnataka, India
2 Radon/Thoron Progeny Research Laboratory, RP and AD, Bhabha Atomic Research Centre, Mumbai, Maharashtra, India
|Date of Web Publication||10-Apr-2015|
B R Kerur
Department of Physics, Gulbarga University, Gulbarga 585 106, Karnataka
Source of Support: Board of Research in Nuclear Studies (BRNS),
Mumbai., Conflict of Interest: None
Radon, thoron and its (α-emitting) decay products contribute to more than 50% of the total effective dose due to natural background radiation. Hence, it is very important to simultaneously measure radon and their progeny concentrations in indoor environment to assess appropriate inhalation dose. In the present work, 222 Rn (CRn ), 220 Rn (CTn ) and their progeny concentrations (EECRn and EECTn ) were measured inside the dwellings of Gogi region, Yadgir District, Karnataka, India. The dwellings were so chosen that they were within 5 km range from the uranium mining area. Measurements were carried out using passive detector systems: Pinhole dosimeters for radon and thoron; deposition based progeny sensors for radon and thoron progeny. The monitoring was carried out during April-July, 2013. The inhalation doses assessed from the measured gas and progeny concentrations in different type of dwellings were found to be within the permissible UNSCEAR limits.
Keywords: Inhalation dose, progeny, radon, Solid State Nuclear Track Detectors, thoron
|How to cite this article:|
Avinash P R, Rajesh S, Kerur B R, Mishra R. Determination of radon, thoron and their progeny concentrations in dwellings of Gogi region, Yadgir District, Karnataka, India. Radiat Prot Environ 2014;37:157-60
|How to cite this URL:|
Avinash P R, Rajesh S, Kerur B R, Mishra R. Determination of radon, thoron and their progeny concentrations in dwellings of Gogi region, Yadgir District, Karnataka, India. Radiat Prot Environ [serial online] 2014 [cited 2020 May 30];37:157-60. Available from: http://www.rpe.org.in/text.asp?2014/37/3/157/154876
| Introduction|| |
Radon, thoron and their progeny, which is a topic of public health concern, has been found to be a ubiquitous indoor air pollutants in homes to which all persons are exposed. Annual exposure due to these nuclei imparts the major contribution to the inhalation dose. Therefore, it is fundamental and justified to make a quantitative assessment of their concentrations in dwellings. In view of the fact that radon, thoron and their progeny concentrations contribute the most to the natural radiation dose to general populations hence large-scale and long-term measurement of radon, thoron and their progeny concentrations has been receiving considerable attention.  The most abundant isotope, 222 Rn is produced by the decay of a naturally occurring radionuclide Ra-226 from U-238 series. In the soil, rocks, and water. Hence, radon is found naturally in certain geological formations like Cave, limestone etc., where 238 U occurs naturally. It is an unstable gas that escapes from the soil and dissipates in the air.
The study area is a region of Yadgir district lies in the northern part of Karnataka between 16° 11'-16° 50' N Latitudes and 76° 17'-77° 28' E Longitudes, which is a plateau, typical of Deccan Trap terrain and is deeply indented with ravines.  The study area selected is of importance because; the soils in these areas contain uranium, naturally-occurring radioactive materials (NORM).  Hence, in the present work, it is reported the radon, thoron and progeny concentration levels inside the dwellings of Gogi region, Yadgir District within the 5 km range from the Uranium mining area for the month April to July, 2013. The data obtained in the present study will be useful for the future researchers to carry out the work in the present region.
| Materials and methods|| |
Exposures were carried out in Gogi region covering the six villages namely Gogi (K), GogiPeth, Singanahalli, Karkalli, Rabanalli, Kanchinakavi. In these villages, a total of 100 dwellings were selected with the different type of houses Reinforced Concrete Construction (RCC), Mud, Rock + wood, Tin and RCC + wood. Measurements were carried out using pin holes-based dosimeters for radon and thoron gas measurements and deposition based and wire-mesh based Direct Radon/Thoron progeny sensors for progeny measurements.
Measurement of radon and thoron activity concentration
Measurement of radon and thoron activity concentrations was carried out using pin holes-based dosimeter, which basically has a single entry for radon and thoron gas, and two chambers for radon and thoron discrimination. LR-115 type Solid State Nuclear Track Detectors (SSNTDs) of 3 × 3 cm 2 is lodged in both the chambers, such that LR-115 in first chamber detects the tracks due to both radon and thoron, while that in the second chamber detects the tracks only due to radon gas. The reason is that only the radon gas enters the second chamber through 4 pin holes of 2 mm length and 1 mm diameter made on a circular disc.
Radon and thoron progeny concentration
For the determination of radon and thoron progeny concentrations, the deposition based and wire-mesh based Direct Radon Progeny Sensor (DTPS)/Direct Thoron Progeny Sensor (DRPS) badges were used. It has two slots for simultaneous measurement of radon and thoron progenies separately. The detector consists of aluminized mylar mounted on an LR-115 detector which acts as a deposition surface for both radon and thoron progeny. In DTPS, a film with a mylar of 50 μm selectively detects the 8.78 MeV alpha particles emitted from 212 Po; while the DRPS has an absorber combination comprising of aluminized mylar and cellulose nitrate with effective thickness of 37 μm to detect mainly 7.69 MeV alpha particles from 214 Po. In a similar way, the films were loaded in the wire-mesh capped DTPS/DRPS badges which selectively detect the attached fraction of the progeny concentration of both radon and thoron separately.
Deployment details and analysis
The dosimeters both pinhole as well as DTPS-DRPS were deployed in indoor environments of 6 villages in Gogi region, such that they were at least 2 m above the ground level and at least 30 cm away from any of the wall/surfaces. The measurements were carried out for a period of 3 months from April to July, 2013. After the exposure of 3 months, the detectors were retrieved and etched in 2.5 N NaOH solution at 60°C for 90 minutes without stirring. ,, The films were then cleaned in running water, dried, peeled and the track counting was done using a spark counter with a voltage of 500V. The track density is converted into activity concentration using appropriate calibration factors.
The calibration factors used for the pinholes dosimeters are, for radon + thoron chamber was 0.010 Tr cm -2 d -1 /Bq m -3 and that for only radon chamber was 0.017 Tr cm -2 d -1 /Bq m -3 .  For deposition based DTPS and DRPS, the calibration factors were 0.94 Tr cm -2 d -1 /Bq m -3 and 0.09 Tr cm -2 d -1 /Bq m -3 respectively.  For wire-mesh capped DTPS and DRPS, the calibration factors were 0.33 Tr cm -2 d -1 /Bq m -3 and 0.04 Tr cm -2 d -1 /Bq m -3 respectively. 
Estimation of inhalation dose (D) and equilibrium factor (F)
The annual inhalation dose in the present study region is calculated using the following relation
where, CRn and CTn are the concentration of radon and thoron in Bq/m 3 , EECRn and EECTn are the respective radon and thoron progeny concentrations. 0.17 and 0.11 (nSv/Bq/m 3 /h) are the dose conversion factors for radon and thoron gas, 9 and 40 (nSv/Bq/m 3 /h) are the dose conversion factors for radon and thoron progenies, 8760 h/y is the indoor occupancy time, 0.8 is the Indoor occupancy factor. 
The equilibrium Factor for radon and thoron in the present study region was calculated using the following relation
where, FR and FT are the equilibrium Factor for radon and thoron respectively, CRn and CTn are the concentrations of radon and thoron respectively calculated using track density from Pin hole compartment and EECRn and EECTn are the Equivalent Equilibrium Concentration of radon and thoron respectively. ,
| Results and discussion|| |
The mean values of 222 Rn, 220 Rn, and their progeny activity concentrations along with dose rates exposed for 3 months in the different locations of Gogi region are summarized in [Table 1]. The arithmetic mean of 222 Rn concentration (CRn ) of Gogi region varies from 25.3 ± 4.8 to 38.7 ± 8.5 Bq/m 3 with a mean of 31.4 ± 6.8 Bq/m 3 , whereas for 220 Rn concentration (CTn ) of Gogi region it varies from 21.0 ± 5.0 to 33.7 ± 9.2 Bq/m 3 with a mean of 26.7 ± 7.0 Bq/m 3 . The result obtained shows that radon and thoron concentrations are comparable in this region. The study area was selected mainly because the soils in these areas contain uranium, naturally-occurring radioactive materials (NORM) and it was 5 km within mining region. Yet, in the indoor environments no such high activity concentrations were recorded. In fact, the radon, thoron gas concentrations were found to be similar to anywhere in India.  The mean equilibrium factor for radon in the present region was found to be ranging from 0.32-0.37 with a mean of 0.35.  The mean equilibrium factor for thoron in the present region was found to be ranging from 0.03 to 0.04 with a mean of 0.04. ,
|Table 1: The mean 222Rn, 220Rn and their progeny concentrations in the dwellings of Gogi region |
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The arithmetic mean of 222 Rn progeny concentration (EECRn ) of Gogi region varies from 8.6 ± 1.3 Bq/m 3 to 14.2 ± 4.7 Bq/m 3 with a mean of 11.0 ± 3.4 Bq/m 3 , whereas for 220 Rn progeny (EECTn ) of Gogi region varies from 0.7 ± 0.1 Bq/m 3 to 1.3 ± 0.4 Bq/m 3 with a mean of 1.0 ± 0.3 Bq/m 3 . The arithmetic mean of annual inhalation dose due to radon, thoron and their progeny in Gogi region varies from 0.8 ± 0.1 Bq/m 3 to 1.3 ± 0.4 Bq/m 3 with a mean of 1.0 ± 0.3 Bq/m 3 .
The attached fraction of progeny concentration marked as EECWRn for radon and EECWTn for thoron in [Table 1] was also found to be very close to the total progeny concentration. This indicates very low unattached fraction.  Further the studies on the seasonal variation in Gogi and other villages will be carried out. The lower values of 222 Rn, 220 Rn and progeny activity concentrations were observed in Singanahalli village whereas higher at the Gogi (K) village.
| Conclusions|| |
In the present study, the mean value of radon concentration is well within the Indian average (42 Bq/m 3 ) and world average (40 Bq/m 3 ) values.  The 2 nd set of simultaneous long time averaged radon, thoron and progeny concentration measurements were carried out in around 100 dwellings of Gogi region during April to July, 2013. The thoron concentrations were found to be comparable with radon gas concentrations [Figure 1]. The progeny concentrations were found to be in the same range as reported in other regions [Figure 2]. These results show a higher concentration of radon in comparison with thoron. Here the radiation doses resulting from exposures to thoron and its progeny cannot be neglected in epidemiological studies because sometimes they can be more significant contributors than radon due to their high concentration and dose conversion factors.  The globally assumed value of F-factor and our experimentally obtained value are in good agreement. The average annual inhalation dose in the present study found to be 1 mSv, which is within the UNSCEAR limits.  A detailed study is in progress in order to find the possible health effects to the people living in the area.
|Figure 1: The mean 222Rn and 220Rn concentrations in the dwellings of Gogi region|
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|Figure 2: The mean 222Rn and 220Rn progeny concentrations in the dwellings of Gogi region|
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| Acknowledgements|| |
The authors are thankful to Board of Research in Nuclear Science (BRNS) for providing the financial support to carry out this work. The authors are also thankful to the members of Radon/Thoron Progeny Research Laboratory, RP and AD, BARC, Mumbai for their help in carrying out intercomparison exercises. The cooperation extended by all the residents of Gogi region is highly appreciated.
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[Figure 1], [Figure 2]