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ARTICLE
Year : 2011  |  Volume : 34  |  Issue : 4  |  Page : 267-269  

Radiation levels and radionuclide distributions in soils of the gogi region, a proposed uranium mining region in north Karnataka


1 University Science Instrumentation Center, Mangalore University, Mangalagangothri, Mangalore, India
2 Department of Soil Physics, Agricultural University, Bhimarayanagudi, Shahpur, India
3 Environmental Assessment Division, BARC, Mumbai, India

Date of Web Publication17-Jan-2013

Correspondence Address:
N Karunakara
University Science Instrumentation Center, Mangalore University, Mangalagangothri, Mangalore
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.106196

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  Abstract 

This paper reports the results of systematic studies aimed at generating a baseline database on the radiation levels and radionuclide distribution in the Gogi region, which has been identified as a prospective uranium mining region. A total of 39 villages in a 0-30 km radius zone of the Gogi region were covered under this study. The ambient gamma absorbed dose rates were measured using portable gamma dosimeters. The activity concentrations of 226 Ra, 232 Th, and 40 K in the soil samples were measured by the HPGe gamma spectrometry method. The ambient gamma absorbed dose rate varied in the range of 126-428 nGy h -1 , with a median value of 143 nGy h -1 . The activities of 226 Ra, 232 Th, and 40 K in the soil varied in the range of 5-176 Bq kg -1 , 9-687 Bq kg -1 , and 81-1493 Bq kg -1 , with the corresponding median values of 36 Bq kg -1 , 85 Bq kg -1 , and 859 Bq kg -1 , respectively. The study showed a highly non-uniform distribution of primordial radionuclides in the soil, with activity concentrations varying significantly within a small area. The results observed in the present study were compared with the literature values reported for other parts of India and the worldwide average values, and discussed.

Keywords: Gamma-absorbed dose, gamma spectrometry, Gogi, natural radioactivity


How to cite this article:
Yashodhara I, Karunakara N, Kumar K S, Murthy R, Tripathi R M. Radiation levels and radionuclide distributions in soils of the gogi region, a proposed uranium mining region in north Karnataka. Radiat Prot Environ 2011;34:267-9

How to cite this URL:
Yashodhara I, Karunakara N, Kumar K S, Murthy R, Tripathi R M. Radiation levels and radionuclide distributions in soils of the gogi region, a proposed uranium mining region in north Karnataka. Radiat Prot Environ [serial online] 2011 [cited 2020 Jul 7];34:267-9. Available from: http://www.rpe.org.in/text.asp?2011/34/4/267/106196


  1. Introduction Top


Gogi (16° 44' 00" N, 76° 45' 00 E), a village in the Shahapur taluk in the Yadgiri district of Karnataka, India, has been identified as a prospective uranium mining area. A preoperational study to establish a baseline database on radioactivity and trace element concentrations in different environmental matrices around the proposed uranium mining area is essential, because such a study would help to assess the radiological impact of long-term mining operations on the environment, in future. Hence, a detailed study aimed at generating a baseline database has been initiated. This article presents the results of external gamma radiation dose rate measurements and activity concentrations of 226 Ra, 232 Th, and 40 K in the soil samples of the Gogi region.


  2. Materials and Methods Top


To start with, the Gogi region was divided into three different zones (0-5 km zone, 5-15 km zone, and 15-30 km zone), [Figure 1], with the proposed mining site as the center, for sampling purpose. Sampling locations were identified in all the three zones and the latitude and longitude were noted using the Global Positioning System (GPS). The ambient gamma absorbed dose rates were measured in the identified locations using three GM tube-based dosimeters simultaneously - (i) ER709 (Nucleonix, Hyderabad) (ii) RDS-31 gamma dosimeter (Mirion, France), and (iii) AlphaGuard (Genitron, Germany).
Figure 1: Map showing the study region and sampling locations

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Surface soil samples from 0-5 cm soil profile were collected from 39 locations. The samples were processed following the standard procedures (BARC, 2008) [1] and the activity concentrations of 226 Ra, 232 Th, and 40 K in these samples were determined by gamma spectrometry, employing a 42% relative efficiency, n-type, low-background HPGe detector, having an energy resolution of 2.0 keV at 1.33 MeV. The spectrum was acquired and analyzed by using a PC-based 16 K multichannel analyzer (DSA-1000, CANBERRA) and the GENIE-2000 software. The detector efficiency calibration was performed using IAEA quality assurance reference materials RGU-238, RGTh-232, and RGK-1. The minimum detection levels (MDL) for the detecting system used in this study were 0.9 Bq kg -1 , 1.2 Bq kg -1 , and 4.0 Bq kg -1 , respectively, for 226 Ra, 232 Th, and 40 K, for a counting time of 60,000 seconds and for a sample weight of 300 g.


  3. Results and Discussion Top


The gamma absorbed dose rates (measured in situ by using gamma dose survey meters) in the 0-30 km zone varied in the range of 126-428 nGy h -1 , with a median value of 143 nGy h -1 [[Table 1], Column 5]. The median value of the absorbed dose rates was higher in the 0-5 km zone when compared to the other two zones. This was due to the natural mineralization of heavy elements in this zone. The median value of the gamma absorbed dose rates observed in the 0-30 km region of Gogi was higher when compared to the mean values of 80.7 nGy h -1 (Mishra and Sadasivan, 1971) [2] and 88.7 nGy h -1 (Nambi et al., 1987), [3] reported for the different regions of India. The dose rates were also higher when compared to the average value (56 nGy h -1 ) reported for normal background areas of the world (UNSCEAR, 2008). [4]
Table 1: Gamma absorbed dose rate in Gogi region

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The concentrations of 226 Ra, 232 Th, and 40 K in the soil samples varied in the ranges of 5-176 Bq kg -1 , 9-687 Bq kg -1 , and 81-1493 Bq kg -1 , respectively, taking into consideration all the locations in the 0-30 km region [Table 2]. The study revealed a highly non-uniform distribution of these natural radionuclides in the region, with activity concentrations in the soil varying significantly within a small area, which was due to highly localized natural mineralization. The median values of 226 Ra and 232 Th activities were found to be higher in the 0-5 km zone and lowest in the 15-30 km zone. [Figure 2] shows the correlation plot of 226 Ra and 232 Th activities in the soil. A significant positive correlation was observed between these radionuclides and the value of the correlation coefficient was R = 0.877 for N = 100 [Figure 2]. The correlation between the activity concentrations of 226 Ra and 40 K was also found to be significant with R = 0.47 (N = 100) and between 40 K and 232 Th, with R = 0.45 (N = 100).
Figure 2: Correlation between activity concentrations of 226Ra and 232Th

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Table 2: Activity concentrations of 226Ra, 232Th and 40K in soil samples of Gogi region

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From the values of activity concentrations of 226 Ra, 232 Th, and 40 K, the absorbed dose rates were calculated using the dose coefficients given in UNSCEAR (2008). The total absorbed dose rate, thus calculated, was found to vary in the range of 14-541 nGy h−1 , with a median value of 106 nGy h−1 . The dose calculated from the primordial radionuclide activity concentrations did not include the cosmic ray component.

The annual effective dose (AED) was also calculated from the gamma absorbed dose (D), calculated from the radionuclides activity concentrations in soil, using the conversion coefficient of 0.7 Sv Gy -1 and an outdoor occupancy factor of 0.2 (UNSCEAR, 2000) as:

AED (μSv y -1 ) = D (nGy h−1 ) × 24 hours × 365 days × 0.2 × 0.7 (Sv Gy -1 ) × 10 -3 (1)

The annual effective dose (AED) was found to be in the range of 17-663 μSv y -1 , with a median value of 128 μSv y -1 . The relative contribution of the primordial radionuclides to the annual effective dose were in the order 40 K > 232 Th > 226 Ra.

A countrywide survey of the outdoor natural gamma radiation levels in India by Nambi et al., (1986), [4] has yielded a national average absorbed dose of 32 nGy h -1 , due to the cosmic ray at sea level. Furthermore, if this value is added to the gamma absorbed dose calculated from the primordial radionuclide concentrations in the soil of Gogi, the total dose turns out to be 160 nGy h−1 , which is comparable to the mean value of the dose measured in situ, using the portable gamma dosimeters.

A comparison of the activity concentrations of primordial radionuclides observed in Gogi region, with those reported for the other regions of India and worldwide average values [Table 3] shows that the 226 Ra concentration was comparable to the average value reported for India (Kamath et al., 1996, Mishra and Sadasivan 1971). [2],[5] The median values of the 232 Th and 40 K activities were higher when compared with the average value reported for India, as also the worldwide average values.
Table 3: Comparison of activity concentrations of 226Ra, 232Th and 40K in soil

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  4. Conclusion Top


Uranium mining has not yet started in Gogi, and therefore, the observed higher concentration of natural radionuclides and the gamma absorbed dose rates in some of the locations is not due to the mining/exploration activities, but primarily due to the natural geological formations of the region. The data presented here represent the baseline levels of radionuclide distribution, as the measurements have been carried out well before the mining activity has started in Gogi. The data generated from this study would help in the assessment of the impact of mining activities in the region.


  5. Acknowledgements Top


The authors would like to thank the Board of Research in Nuclear Science, Department of Atomic Energy, India, for providing financial assistance for the research project. Investigators would like to thank the Chairman and all the members of the BRNS-NRFC Committee for many useful suggestions. The authors are thankful to all the officials and scientific staff of NFC, Hyderabad, and AMD, Hyderabad, for their help and cooperation. The authors are also thankful to the teaching staff of the Department of Soil Physics, Agricultural University, Bhimarayanagudi, Shahpur, and the administrative staff of this University, for permitting the use of the laboratories for sample processing.

 
  References Top

1.Hegde AG, Varma PC, Rao DD. Standard protocol for evaluation of environmental transfer factors around NPP sites. BARC, 2008.  Back to cited text no. 1
    
2.Mishra UC, Sadasivan S. Natural radioactivity levels in Indian Soils. J Sci Ind Res 1971;30:59-62.  Back to cited text no. 2
    
3.Nambi KS, Bapa, VN, David M, Sundaram VK, Santa CM, Soman SD. Country wide environmental radiation monitoring using thermoluminescent dosimeters. Radiat Prot Dosimetry 1987;18:31-8.  Back to cited text no. 3
    
4.United Nations Scientific Committee on the Effects of Atomic Radiation, (UNSCEAR-2008), Report to the General Assembly, Vol. 1, Annex B.  Back to cited text no. 4
    
5.Kamath RR, Menon MR, Shukla VK, Sadasivan S, Nambi KS. Natural and fallout radioactivity measurement of Indian soils by gamma spectrometric technique. Calcutta, India: In: 5 th National Symposium on Environment; 1996. p. 56-60.  Back to cited text no. 5
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]


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