J Radioanal Nucl Chem (2014) 302:1321–1326 DOI 10.1007/s10967-014-3608-x
Radon, thoron and their progeny concentration variations in dwellings of Gogi region, Yadgir district of Karnataka, India P. R. Avinash • S. Rajesh • B. R. Kerur Rosaline Mishra
•
Received: 25 August 2014 / Published online: 29 October 2014 Ó Akade´miai Kiado´, Budapest, Hungary 2014
Abstract The radiation dose due to inhalation of radon, thoron and their progenies constitute a major part (50 %) of the total natural background dose received by a man. Thus measurement of indoor radon in dwellings is very important. In the present study, radon, thoron and their decay product measurements were carried out using passive detector systems, namely the pinholes dosimeters and Direct Radon (Thoron) progeny sensors. These measurements were carried out in indoor environments (different dwelling types) during January–April 2013 for 90 days, in the Gogi region. The timeaveraged mean radon, thoron and decay product concentrations were found to be within the permissible UNSCEAR limits. Keywords Indoor radon Thoron Progeny LR-115 Annual inhalation dose Type of houses
Introduction 222
Rn, a decay product of 226Ra in the naturally occurring U series, is a radioactive inert gas and contributes about half the natural radiation dose. Individuals are subjected to radon exposure through inhalation of air containing radon. Radon is present in soil, water, building materials and in the atmosphere. The concentrations of radon and thoron are higher in indoor than outdoor areas. Among all natural sources of radiation dose to human beings, inhalation of
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P. R. Avinash S. Rajesh B. R. Kerur (&) Department of Physics, Gulbarga University, Gulbarga 585106, India e-mail:
[email protected] R. Mishra Radiological Physics and Advisory Division, BARC, Mumbai 400085, India
radon and its daughter products contributes a significant portion of dose to the general population. The energetic alpha particles emitted from 222Rn and two of its daughter elements viz. 214Po and 212Po are highly effective in damaging the tissue and are considered to be a causative agent for lung cancer in human beings [1]. In a lifetime a living house is at the action level of 200 Bq/m3 carries a 3–5 % risk of fatal cancer [2, 3]. The worldwide mean annual effective dose due to the inhalation of radon, thoron and their decay products is estimated to be 1.2 mSv [4]. Radon (222Rn) and thoron (220Rn) are two main sources of natural radioactivity in the atmosphere out of which radon contributes more than half of all non-medical exposure to ionizing radiation dose received by general population [5]. The measurement of radon in man’s environment is of interest because of its emitting nature of alpha particles. Due to its short half-life (T1/2 = 3.82 d) it diffuses through soil and into the air. Inhalation of the short-lived progeny of radon is responsible of about half of the total effective dose received by humans from all natural sources of ionizing radiation. As these are inert gases therefore it can easily disperse into the environment as soon as it is released. About 90 % of Mean radiation dose received by human from natural sources and about 50 % is due to inhalation of radon, thoron and their progeny present in the dwellings [6]. In dwellings radon and thoron level enter through the cracks, sump, and joints. In poorly ventilated spaces the radon concentration may reach levels of great concern. Radon, thoron and its decay products (218Po and 214Po) attach to aerosols and get trapped in the trachea, bronchial system during inhalation thereby irradiating the bronchial tissues. It constitutes a significant radiation hazard to human lungs and occurrence of lungs cancer [6]. The study area is a region of Yadgir district lies in the northern part of Karnataka between 16° 110 –16° 500 N
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Latitudes and 76° 170 –77° 280 E Longitudes, with a geographical area of 5,234.4 Sq. km. The northern part of the district represents a plateau, typical of Deccan Trap terrain and is deeply indented with ravines. The soil types in the district are deep black, medium black soil, shallow soil and lateritic soil. The deep and medium black soil covers practically the entire district’s area, except a small portion towards the northern part of the district. Lateritic soil occurs in small extent towards the northern part of the district [7]. The data obtained in the present study with pin holes based dosimeter deployed side by side with direct radon progeny sensor (DRPS) and direct thoron progeny sensor (DTPS) badges will provide the future researchers a baseline data for comparison and further environmental radioactivity research of the study region.
Materials and methods The experimental method for the radon and thoron detection and measurements are based on the alpha counting of radon, thoron and their daughter products. Hence the active and passive devices are available in the literature for this purpose. In the present investigations, the passive technique using the solid state nuclear track detectors (SSNTDs) developed by Bhabha Atomic Research Centre (BARC), Mumbai, were used for the survey which is a most reliable technique for the integrated and long-term monitoring of radon has been utilized for the comparative study of the indoor radon level. The LR-115 Type II (Pelliculable) SSNTDs are made of cellulose nitrates which are sensitive to alpha particles. SSNTDs also have the advantage to be mostly unaffected by humidity, low temperatures, moderate heating and light [5]. Selection of indoor environments The present study covers the Gogi region of Yadgir district different types of houses were selected for deployment like reinforced concrete construction (RCC), Mud, Rock ? wood, Tin and RCC ? wood. In this region, the Gogi(K), Gogi Peth, Singanahalli, Karkalli, Rabanalli and Kanchinakavi villages were covered, and 32, 30, 09, 10, 15, 04 houses were selected respectively. So, a total of 100 houses were selected. The study was conducted by measuring the cumulative exposure for a minimum period of about 90 days in each house during Jan– April 2013. Detectors used For indoor radon/thoron measurement, SSNTD based dosimeter known as pinholes dosimeter is used. The LR115 (Type II, pelliculable) films made of Cellulose nitrate
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Fig. 1 Schematic diagram of the pinholes dosimeter
Fig. 2 Photograph of DTPS/DRPS
are used as detectors. The experimental procedure comprise of controlled exposure of LR-115 detector loaded pinholes dosimeters which has a single entry, where gas enters into the 1st chamber (radon ? thoron) through a glass fiber filter paper and then into the 2nd chamber through discriminating pin-hole disc which separates the two chambers. The 1st chamber is the reference chamber and the 2nd one is the pin-hole chamber. Each chamber has a length of 4.1 cm and radius of 3.1 cm [8]. On the other side of the compartment only radon gas was allowed to enter which has a circular disc with a four pin holes of 2 mm length and 1 mm diameter in it (Fig. 1). This pin hole is designed in size and thickness of cap so as to block thoron from entry inside by considering the diffusion length and half life of thoron [9]. For radon and thoron decay products, DTPS-DRPS dosimeters (Fig. 2) were used [10]. It consists of aluminized mylar mounted LR-115 detector which acts as
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for only radon chamber was 0.017 Track/cm2/d/Bq/m3 [8]. For DTPS, the calibration factor was used as 0.94 Track/ cm2/d/Bq/m3 [10] and for DRPS was 0.09 Track/cm2/d/Bq/ m3 [13]. For wire-mesh capped DTPS and the DRPS the calibration factors were 0.33 Track/cm2/d/Bq/m3 and 0.04 Track/cm2/d/Bq/m3 respectively [11]. The annual inhalation dose [14] of the present study region is calculated using the following relation AID ðmSv/y) ¼ ðCRn 0:17 þ CTn 0:11 þ EECRn 9 þ EECTn 40Þ 8; 760 0:8 106 Fig. 3 Photograph of wire mesh capped DTPS/DRPS
deposition surface for separately measuring the radon progeny and thoron progeny, which selectively registers the tracks due to alpha emissions from 214Po and 212Po from the deposited atoms of radon and thoron progeny species, respectively. In order to register the attached component of the progeny atoms, wire-mesh capped DTPS/DRPS (Fig. 3) were used [11]. Dosimeters and DTPS/DRPS badges were together exposed adjacent to each other for the same duration.
where, CRn and CTn are the concentration of radon and thoron in Bq/m3, EECRn and EECTn are the respective radon and thoron progeny concentrations. 0.17 and 0.11 (nSv/Bq/m3/h) are the dose conversion factors for radon and thoron gas, 9 and 40 (nSv/Bq/m3/h) are the dose conversion factors for radon and thoron progenies [4], 8,760 h/y is the indoor occupancy time, 0.8 is the indoor occupancy factor.
Results and discussion Radon/thoron distribution in the indoor environment
Deployment details The pinholes dosimeters along with DTPS-DRPS dosimeters are hanged over on the ceiling of the selected dwellings of Gogi region with 50 cm distance from any wall at a height of more than 1.5 m above the ground level and about 50 cm below the ceilings and away from the walls [13]. Analysis After the exposure for 3 months the detectors were retrieved and some of the exposed films of the Gogi region were taken to the Radon/Thoron Progeny Research Laboratory, RP&AD, BARC, Mumbai for the analysis. The data obtained in this laboratory are verified in our laboratory. Intercomparison calibration exercises were also conducted to verify the correctness of the methodologies adopted. The data obtained using passive methods were also compared with that using active methods using commercially available instruments and were found to be comparable. The films were etched using 2.5 N NaOH solution at 60 °C for 90 min without stirring [5, 9]. Subsequently, the tracks were counted using a spark counter and these counted tracks are converted into the radionuclide concentrations by the use of appropriate calibration factors. For the pinholes dosimeters, the calibration factor for radon ? thoron chamber was used as 0.010 Track/cm2/d/Bq/m3 and that
In the present study, the work is done in the indoor environment where the concentrations of the radon, thoron and their progenies with the annual inhalation dose kept in the dwellings of the six different villages from the field of study have been calculated and are shown in the Table 1. The study was conducted by measuring the cumulative exposure for a minimum period of about 90 days in each house covering 100 houses where the 222Rn and 220Rn and their progeny concentrations were measured for the month Jan–April, 2013. These results support studies, showing equal concentration of thoron in comparison with radon in certain cases (Table 1). The 222Rn and 220Rn and their progeny concentrations have been measured in different type of dwellings located in the Gogi region and the values were found to be within the permissible UNSCEAR limits [4]. 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 graphs were plotted using the mean concentrations of radon, thoron and their progeny versus the no. of houses (Figs. 4, 5). The 222Rn, 220Rn and their progeny concentrations were measured in the dwellings of the Gogi region of Yadgir district. A total of six villages are selected namely Gogi
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Singanahalli Karakalli
Rabanalli
Kanchinakavi
3 4
5
6
SD standard deviation
Mean ± SD
Gogi (K)
Gogi peth
Rn,
1
222
2
Sample location
S. no.
Table 1 The mean
97–100
82–96
63–71 72–81
33–62
1–32
House no.
36 ± 7.1
34 ± 7
35 ± 7.1
29 ± 5.2 37 ± 8
37.3 ± 6.4
43 ± 9.2
Rn conc. in Bq/m3
222
Mean ± SD
11.8 ± 2.4
11.2 ± 2.4
12 ± 2.1
10.2 ± 1.7 12.3 ± 2.4
12 ± 2.6
13.6 ± 3.5
EECRn in Bq/m3
1.1 ± 0.3
1 ± 0.2
1.1 ± 0.3
0.8 ± 0.2 1.2 ± 0.3
1 ± 0.3
1.3 ± 0.4
EECTn in Bq/m3
Progeny gas concentrations (Bq/m3 )
32 ± 7.1
30 ± 7
32 ± 7.1
25.5 ± 4.7 33 ± 9
32.7 ± 5.5
38.1 ± 9.4
Rn conc. in Bq/m3
220
Rn and their progeny concentrations of Gogi region
220
12
10
8
6
4
1.2 2
1.0
0.8
0.6
0.4
0.2
0.0
0.04 ± 0.01
0.03 ± 0.01
0.04 ± 0.01
0.03 ± 0.01 0.04 ± 0.01
0.03 ± 0.01
0.03 ± 0.01
FT
Fig. 4 The mean
Fig. 5 The mean Gogi region
Gogi Peth
Gogi (K) 222
Rn and
222
10
0 33-62 63-71
1-32 33-62 63-71
Rn and
Kanchinakavi
20
Rabanalli
Month: Jan - April Karkalli
222
220
222
220
Month: Jan - April
72-81 82-96
Kanchinakavi
1-32 Singanahalli
30
Rabanalli
3
0.33 ± 0.03
Gas Concentration (Bq/m )
1.1 ± 0.2
0.33 ± 0.02
0.35 ± 0.02
0.35 ± 0.02 0.34 ± 0.02
0.32 ± 0.03
0.32 ± 0.04
FR
Equilibrium factor
40
Karkalli
Singanahalli
14
Gogi Peth
1 ± 0.2
11.4 ± 2.3
1.1 ± 0.3
1.1 ± 0.2
0.9 ± 0.2 1.2 ± 0.3
1.1 ± 0.2
1.3 ± 0.3
Annual inhalation dose (AID) in mSv/y
50
Gogi (K)
1 ± 0.3
0.7 ± 0.2 1.1 ± 0.3
9.7 ± 1.5 11.7 ± 2.3 0.9 ± 0.2
1 ± 0.2
10.9 ± 2.2
1.2 ± 0.3
13.2 ± 3.4 11.7 ± 2.6
11.5 ± 2
EECWTn in Bq/m3
EECWRn in Bq/m3
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Rn Concentration Rn Concentration
House No.
72-81 82-96 97-100
220
Rn concentrations of the Gogi region
Rn Progeny Rn Progeny
House No. 97-100
220
Rn progeny concentrations of the
(K), Gogi Peth, Singanahalli, Karkalli, Rabanalli, and Kanchinakavi, where the 100 pinholes dosimeter along with DTPS/DRPS are kept. The mean values of 222Rn, 220 Rn, and their progeny activity concentrations along with dose rates in the different locations of Gogi region are summarized in Table 1. It is observed that, the arithmetic mean of 222Rn concentration (CRn) of Gogi region varies from 29 ± 5.2 to 43 ± 9.2 Bq/m3 with a mean of 36 ± 7.1 Bq/m3, whereas for 220Rn concentration (CTn) of Gogi region it varies from 25.5 ± 4.7 to 38.1 ± 9.4 Bq/m3 with a mean of 32 ± 7.1 Bq/m3.
J Radioanal Nucl Chem (2014) 302:1321–1326 Table 2 The mean Type of houses
222
Rn,
220
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Rn and their progeny concentrations with type of houses
Mean ± SD 222
Rn conc. in Bq/m3
220
Rn conc. in Bq/m3
222
13.2 ± 3.1
Rn progeny conc. in Bq/m3
RCC
40.4 ± 8.6
35.7 ± 7.7
Rock ? Wood
32.5 ± 5.8
28.8 ± 5
Mud
40.6 ± 9.8
36.4 ± 10.7
11 ± 1.4 13.2 ± 3.4
220
Rn progeny conc. in Bq/m3
Attached radon progeny conc. in Bq/m3
Attached thoron progeny conc. in Bq/m3
Annual inhalation dose (AID) in mSv/y 1.2 ± 0.3
1.2 ± 0.4
12.7 ± 3.1
1.1 ± 0.3
1 ± 0.2
10.5 ± 1.4
0.9 ± 0.2
1 ± 0.1
1.2 ± 0.4
12.8 ± 3.3
1.1 ± 0.3
1.2 ± 0.3
Tin
33.8 ± 4.2
30 ± 5.6
11.1 ± 1.7
1 ± 0.2
10.6 ± 1.4
0.9 ± 0.2
1 ± 0.1
RCC ? Wood
35.3 ± 5.5
30.7 ± 4.9
10.9 ± 1.9
1 ± 0.2
10.6 ± 1.9
0.9 ± 0.1
1 ± 0.2
SD standard deviation
220
Month: Jan - April
Gas Concentration (Bq/m 3 )
40
222
Rn Concentration Rn Concentration
35 30 25 20 15 10 5 0
220
14
Progeny gas concentration (Bq/m3 )
222
Rn progeny Rn progeny
Month: Jan - April
12 10 8 6 4 2 1.2 1.0 0.8 0.6 0.4 0.2 0.0
RCC
Rock+Wood
Mud
Tin
RCC+Wood
RCC
Rock+Wood
Type of Houses 222
Fig. 6 The mean Rn and with type of houses
220
Rn concentrations of the Gogi region
The arithmetic mean of 222Rn progeny concentration (EECRn) of Gogi region varies from 10.2 ± 1.7 Bq/m3 to 13.6 ± 3.5 Bq/m3 with a mean of 11.8 ± 2.4 Bq/m3, whereas for 220Rn progeny (EECTn) of Gogi region varies from 0.8 ± 0.2 Bq/m3 to 1.3 ± 0.4 Bq/m3 with a mean of 1.1 ± 0.3 Bq/m3. The EECTn is low compared with EECRn due to the short half life of thoron (T1/2 = 55 s). The arithmetic mean of annual inhalation dose of the Gogi region varies from 0.9 ± 0.2 mSv/y to 1.3 ± 0.3 mSv/y with a mean of 1.1 ± 0.2 mSv/y. In the present study, the thoron concentration was also found to be higher as radon concentration. The higher value of thoron in the present region may be due to presence of high concentration of natural radionuclide minerals in the local geological formations. The high value of radon and thoron progeny concentrations with time-integrated measurements indicates that long time exposure of radon and thoron progenies to the human beings can produce high radiation doses. Simultaneously, the annual
Mud
Tin
RCC+Wood
Type of Houses 222
Fig. 7 The mean Rn and 220Rn progeny concentrations of the Gogi region with type of houses
inhalation dose rate was also measured in indoor environment of the study area. The mean annual inhalation dose in the present study was found to be 1.1 mSv. The mean equilibrium factor for radon in the present region was found to be ranging from 0.32 to 0.35 with a mean of 0.33. 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. This shows that, the data measured in the present region are in good agreement with the literature results [13, 16]. Radon/thoron distribution with construction types of buildings Also the graphs of 222Rn, 220Rn and their progeny concentrations of Gogi region were also been plotted versus the construction type of houses (Table 2). It can be observed that the RCC and mud type of houses have the
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highest concentrations of radon, thoron and their progeny [15] compared to Rock ? wood, Tin and RCC ? Wood type of houses (Figs. 6, 7).
Conclusion The results show that overall concentration of radon, thoron and their progeny in the study area are low compared to that of the level found in high background radiation areas like the western coast of Kerala [12]. The 1st set of simultaneous long time Mean radon, thoron and progeny concentration measurements were carried out in around 100 dwellings of Gogi region during the month Jan–April, 2013. The thoron concentrations were observed to be almost equal to radon gas concentrations. The progeny concentrations were found to be in the same range as reported in other regions. The analyses of the successive sets are in progress. The mean annual inhalation dose in the present study is found to be 1.1 mSv which is within the UNSCEAR limits. These results support studies, showing higher concentration of radon in comparison with thoron. The contribution to the total dose by thoron was also found to be more. This shows that the radiation doses produced by 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. Acknowledgments The authors are thankful to Board of Research in Nuclear Sciences (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&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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