|Year : 2011 | Volume
| Issue : 1 | Page : 55-59
Natural radioactivity levels in some environmental samples of Shahpur Region of North Karnataka, India
BR Kerur1, T Rajeshwari1, NM Nagabhushana1, S Anilkumar2, K Narayani2, AK Rekha2, B Hanumaiah3
1 Department of Physics, Gulbarga University, Gulbaga, India
2 Radiation Safety Systems Division, BARC, Mumbai, India
3 Vice-Chancellor, Babasaheb Bhimrao Ambedkar University, Lucknow, India
|Date of Web Publication||17-Mar-2012|
B R Kerur
Department of Physics, Gulbarga University, Gulbaga
Source of Support: None, Conflict of Interest: None
The natural radioactivity due to Radium, Thorium and Potassium in environmental samples such as soil and building materials contributes to the radiation dose received by human beings significantly. For assessing the environmental radiological impact to public it is essential to evaluate the activity levels of these nuclides. Using high-resolution Gamma ray spectrometry system the soil and few building material samples viz., granite, sand, brick collected from Shahpur region of North Karnataka were analysed and the radioactivity levels were estimated. The absorbed dose rate due to natural radionuclides was also calculated and the results are reported in this paper. The results obtained were observed to be normal in comparison with the World literature values for almost all samples whereas granite samples showed relatively higher activity and hence higher dose. This study provides a baseline data of radioactivity background levels in the Shahpur region of Gulbarga district and will be useful to assess any changes in the radioactive background level due to various man made processes.
Keywords: Natural radioactivity, radionuclide, radioactive equilibrium
|How to cite this article:|
Kerur B R, Rajeshwari T, Nagabhushana N M, Anilkumar S, Narayani K, Rekha A K, Hanumaiah B. Natural radioactivity levels in some environmental samples of Shahpur Region of North Karnataka, India. Radiat Prot Environ 2011;34:55-9
|How to cite this URL:|
Kerur B R, Rajeshwari T, Nagabhushana N M, Anilkumar S, Narayani K, Rekha A K, Hanumaiah B. Natural radioactivity levels in some environmental samples of Shahpur Region of North Karnataka, India. Radiat Prot Environ [serial online] 2011 [cited 2020 Jan 28];34:55-9. Available from: http://www.rpe.org.in/text.asp?2011/34/1/55/93956
| 1. Introduction|| |
Radiation is present everywhere in the environment of earth, below the earth and in the atmosphere. Man knowingly or unknowingly is continuously being exposed to the radiation, nature itself being the significant source of radiations. Radionuclides are found naturally in air, water and soil and even in human body. Natural radioactivity is common in granites, soil, sand, water and building materials present around us. Natural background radiation is of terrestrial and extraterrestrial origin (UNSCEAR, 2000). The main contribution to terrestrial background radiation is from naturally occurring radionuclides 226 Ra, 232 Th and their daughter products and singly occurring natural radionuclides such as 40 K, 87 Rb present in varying amounts in soil, rocks, granites and building materials. Some of the radionuclides from these sources are transferred to man through ingestion or inhalation, while the extraterrestrial radiation originates from outer space as primary cosmic rays. Furthermore, because of the occurrence of radionuclides in soil and in vegetation, exposures will occur as a result of ingestion (El-Arabi, 2007).The environmental radioactivity and associated external exposure due to gamma radiation from the environmental materials like soil, rock, water etc., depend mainly on the geological formation and composition of the region (Ramola et al., 2008). Hence it is present everywhere within us and surrounding environment in different concentrations. Also it is found by many researchers that the accumulated dose can be high even though activity of these materials is at low level (low level radioactivity). Around the world there are some areas with sizable population that have high background radiation levels. The high background radiation areas are found primarily in Brazil, India and China (Nambi et al., 1994; Baranwal et al., 2006). Due to the advanced technology and modernization a person is prone to the internal and external radiation and knowledge of natural radioactivity and the determination of amount of radiation dose received become important.
Soil and other environmental materials are important components of environment that not only contains compounds that support life but also contains significant quantity of various radionuclides such as 232 Th, 226 Ra, 222 Rn, 40 K etc. the gamma radiations emitted from which are harmful to the life. External gamma dose rates depend on the activity concentrations of the natural primordial radionuclides 232 Th, 226 Ra and their decay products and 40 K present in soil and rock, which in turn depend on the rock formation and geological composition of the region.
In this context, the present work involves the estimation of activity of the primordial radionuclides and associated radiation dose received from soil and building material (granite, sand, brick) samples collected from Shahpur region of Gulbarga district of North Karnataka. The study will provide a baseline data of natural background radiation level of the region, which is essential for understanding the future changes in natural background radiation of the region, as there are no earlier results.
| 2. Geology of The Area Under Study|| |
The area under study represents a part of N-E Karnataka, which is well known for granite production and also taking part in iron, manganese and gold ore mining operations. The present work has been carried out in Shahpur region of Gulbarga district of North Karnataka, India. The Shahpur region lies in the North latitude 15° 50' and East longitudes 74° 34'. The study region is rich in granitic rocks which demarcate the Archaean nucleus. A large deposit of uranium has been found in one of the villages Gogi of Shahapur and it is important to study the distribution of radionuclides in the surrounding regions.
| 3. Materials and Methods|| |
Standard procedures were followed for sample collection and preparation, where surface soil over an area 50 cm × 50 cm and 5 cm depth was mixed thoroughly and about 2-3 kg of each sample was collected. The details of the collected samples were noted and then coded. The first two letters correspond to the type of sample, next two digits correspond to district place (Gulbarga-01), next two correspond to taluk's place (Shahpur-07) and last two correspond to serial number. These samples were pulverized to a fine powder and then sieved. The samples were then placed for drying at 110°C for 24 hour to ensure that the moisture is completely removed. Each coded pulverized sieved sample was then transferred to a 250 ml cylindrical plastic container. The containers were then weighed and sealed carefully from outside using an adhesive and stored for four to five weeks to attain secular equilibrium between 226 Ra and 222 Rn and it's decay products.
The samples were analyzed using a high-resolution gamma spectrometry system. The system comprises of a high purity Ge (HPGe) detector with a relative efficiency of 50% and full width at half maximum (FWHM) of 2 keV for 1.332 MeV γ-ray line of 60 Co. The output of the detector was analyzed using a PC based 8k multichannel analyzer system (GAMMAFAST, Eurosys Mesures). The detector was surrounded by 3" lead shield on all sides to reduce the background radiations originating from building materials and cosmic rays (Anilkumar et al., 2001). Efficiency calibration for the system was carried out using the standard uranium ore (RGU, IAEA) in geometry available for the sample counting. The samples were counted for a period of 60,000 seconds and the spectra were analyzed for the photo peaks due to radium, thorium daughter products and 40 K. The net count rate under the most prominent photo peaks of radium and thorium daughter peaks were calculated and the background count rate was subtracted from the respective count rate. Then the activity of the nuclide was calculated from the prominent gamma energies viz., the 226 Ra activity was estimated using the 295.1 keV and 351.9 keV gamma energies emitted by 214 Pb and 609.3 keV and 934.0 keV emitted by 214 Bi and 186.1 keV emitted by 226 Ra and determination of the activity from 232 Th is based on the detection of gamma rays 238.6 keV from 212 Pb, 338.5 keV and 911.2 keV from 228 Ac and 583 keV from 208 Tl and 1620 keV from 212 Bi. The activity of 40 K is based on the detection of it's 1460.8 keV gamma ray. The integral counts under preselected photopeaks were determined by subtracting from the total counts under corresponding photopeaks obtained for the background (taken with an empty container under identical geometry). Then the activity of the nuclide was calculated from the prominent gamma energies using:
Activity (Bq) = (Net area under PP cps × 100 × 100) / (Efficiency (%) × BR (%))
| 4. Results and Discussion|| |
The results observed for the 226 Ra, 232 Th and 40 K activity concentrations obtained for each of the measured sample together with their corresponding total uncertainties are summarized in [Table 1]. The concentration of thorium, radium and potassium are in the range from 18.46 to 122.4 Bq/kg, 11.75 to 97.5 Bq/kg and 197.8 to 1340 Bq/kg respectively. The mean activity of the three radionuclides was observed to be 38.86 Bq/kg, 18.94 Bq/kg, and 546.3 Bq/kg respectively for the soil samples and 67.67Bq/kg, 45.28 Bq/kg and 806.6 Bq/kg for the building material samples of Shahpur region. A correlation was studied between 226 Ra and 232 Th for the soil samples of the study region shown in [Figure 1]. Radium and thorium activity demonstrated a positive correlation with a coefficient of 0.5733 which is low and predicts a slight geochemical incoherency between the samples collected from Shahpur region. The correlation plots between 226 Ra and 232 Th for all the building material samples showed a good positive linear correlation of value 0.9530 [Figure 2] which predicts that the radium and thorium activity are geologically and geochemically coherent in case of building materials of the study region. A correlation between the granite samples showed a good positive correlation of 0.9984 between three granite samples as in [Figure 3] which shows that radium is intrinsic in country rock at Shahapur and geochemical coherency is maintained.
|Figure 1: Correlation between 232Th and 226Ra activity for Shahapur region soil samples|
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|Figure 2: Correlation between 232Th and 226Ra activity for Shahapur region building materials' samples|
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|Figure 3: Correlation between 232Th and 226Ra activity for Shahapur region granite samples|
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|Table 1: Activity, total absorbed gamma dose rate and dose equivalents for the different soil samples|
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To assess the radiation hazard, the UNSCEAR (2000) has given the dose conversion factors for converting the activity concentrations of 226 Ra, 232 Th and 40 K into absorbed dose (nGy h -1 per Bqkg -1 ) as 0.462, 0.604 and 0.0417 respectively. Using these factors, the total absorbed gamma dose rate in air at 1m above the ground level is calculated by using the formula:
D = (0.604C Th + 0.462C Ra + 0.0417C K) nGyh-1
Where, C Ra , C Th and C K are the activity concentrations of Radium, Thorium, and Potassium in the samples in Bq/kg respectively. It is clearly observed from the [Table 1] that the mean gamma absorbed dose rate for soil is 55.01nGy h -1 and 92.03 nGy h -1 for building material samples. Annual effective dose equivalent received by a member is estimated using a conversion factor of 0.7 SvGy -1 , with an outdoor occupancy of 20% assuming that a person spends about 80% of his time indoors (UNSCEAR, 2000). In the present case the annual effective dose equivalent received from soil and building material samples of Shahapur region is estimated to be 267.5 μ Svy -1 and 453.6 μ Svy -1 . It can be observed from the table that the building material samples especially granite samples show a higher activity hence higher dose which is not ignorable and may pose radiological hazards in due future. The use of these materials for construction purposes has to be given a second thought from radiological point of view. In [Table 2] gives the comparison of the activity of radionuclides and dose rate measured from the study area with the national and international literature values. Our measured values are well within the national and UNSECAR 2000 reported values.
|Table 2: Comparison of the activities of radionuclides and dose rate in soil samples of Shahapur with other literature values of the world|
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| 5. Conclusion|| |
The results obtained have shown that the total effective dose rate due to natural radioactivity of soil varies from 223 to 572 μSvy -1 , which infer that the radiations are natural background radiations. The present study shows that the values obtained in the present study are well comparable with the national and international values. Hence the study of natural radiation background of this area is quite constant with other literature values (places) and also over the period of time i.e., these values practically independent of human practices and activities at present. Further work is continued on varieties of the samples in and around of this region (Rajeshwari, 2008 and Nagabhushan, 2009).
| 6. Acknowledgements|| |
The authors are thankful to Dr. D.N. Sharma, Head, RSSD, for his interest in this work and for analysing the samples at their Laboratory. Authors are also grateful to Shri D.A.R. Babu, Head, RMS and TS, RSSD, for his encouragement and support in this work.
| 7. References|| |
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]