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ORIGINAL ARTICLE
Year : 2013  |  Volume : 36  |  Issue : 1  |  Page : 10-13  

Radioactivity measurements in the environment of Chamaraja Nagar area, India


Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore, Karnataka, India

Date of Web Publication21-Nov-2013

Correspondence Address:
M S Chandrashekara
Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore, Karnataka
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0972-0464.121812

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  Abstract 

The knowledge of distribution of radionuclides and radiation levels in the environment is important for assessing the effects of radiation exposure to human beings. Terrestrial radiation is due to the radionuclides present in different amounts in rocks, soils, building materials, water and atmosphere. Radon is the main natural radiation source of exposure of human beings and has been recognized as a carcinogenic gas. Radium ( 226 Ra) and its ultimate precursor uranium ( 238 U) are the parent sources of radon. In the present study, radon exhalation rate and radium concentration in soil and rock samples around Chamaraja Nagar area of Karnataka State, India are measured using solid state nuclear track detector's employing "can technique" and LR-115 Type-II detectors. The result from the present investigation shows that radium activity in rock sample varies from 2.9 to 39.5 Bq/kg with a geometric mean of 13.4 Bq/kg. Mass and surface exhalation rate of radon in rock samples varies from 8.0 to 119.7 mBq/kg/h with the geometric mean of 24.8 mBq/kg/h and 93.9-1787.3 mBq/m 2 /h with a geometric mean of 562.5 mBq/m 2 /h respectively. Radium concentration in soil samples has been found to vary from 3.6 to 34.1 Bq/kg with a geometric mean of 14.7 Bq/kg. The mass exhalation rate of radon in soil samples has been found to vary from 10.0 to 31.4 mBq/kg/h with a geometric mean of 18.6 mBq/kg/h. The surface exhalation rate of radon varies from 142 to 918.4 mBq/m 2 /h with a geometric mean of 391.5 mBq/m 2 /h.

Keywords: Chamaraja Nagar, radon exhalation, solid state nuclear track detector


How to cite this article:
Nagaraju K M, Chandrashekara M S, Pruthvi Rani K S, Rajesh B M, Paramesh L. Radioactivity measurements in the environment of Chamaraja Nagar area, India. Radiat Prot Environ 2013;36:10-3

How to cite this URL:
Nagaraju K M, Chandrashekara M S, Pruthvi Rani K S, Rajesh B M, Paramesh L. Radioactivity measurements in the environment of Chamaraja Nagar area, India. Radiat Prot Environ [serial online] 2013 [cited 2020 Feb 27];36:10-3. Available from: http://www.rpe.org.in/text.asp?2013/36/1/10/121812


  Introduction Top


Nearly 95% of human radiation exposure arises from natural sources, such as cosmic radiation, radon gas and terrestrial radiation. Radium ( 226 Ra) is a solid radioactive element, which decays in to radon by emitting alpha particles. Ionizing radiation exposure, experienced by the general population is mainly due to indoor radon. Exposure of persons to high concentrations of radon and its progeny for a long period may lead to pathological effects and occurrence of lung cancer. [1] The exhalation rate of radon from soil to atmosphere depends on the temperature gradient between the different layers of the soil and other meteorological conditions. [2] The bedrock have a high content of radium, when the bedrock gets destroyed and fissured, 222 Rn and 220 Rn gases diffuse into the dwellings. [3] The radon emanated from the grains of the sample, diffuses and migrated through the pores of the sample and exhaled from the sample surface. Fick's diffusion laws - explain this transport mechanism, by considering porosity of the sample and radon production rate through emanation. [4],[5],[6],[7] Emanation of radon gas signifies the presence of uranium ( 238 U) in the soil/rocks. The inhalation and ingestion of these radionuclides above the permissible levels become a health hazard. Therefore, the study and measurements of radium concentration and radon exhalation rate is necessary for, the assessment of public health risk. [8]


  The Study Area Top


The geographical area of Chamaraja Nagar district is about 5101 km 2 and has a population of about one million. The district is located in the southern tip of Karnataka State and lies between North latitude 11°40'58" and 12°6'32" and East longitude 76°24'14" and 77°64'55". It has an average elevation of 662 m. It consists of four taluks viz., Chamaraja Nagar, Gundulpet, Kollegal and Yalandur. The southern part of Chamaraja Nagar District is surrounded by Kerala and Tamil Nadu states. The district has a forest cover of about half of the total area and has vast reserves of black granite. Temperature varies from minimum 10°C to maximum 32°C. The district receives less rain fall with an average of 951 mm. Bandipura National Park, B. R. Hills, M. M. Hills and Gopalaswamy Hills are important Hilly areas of the district. This district is endowed with rich mineral resources, both metallic and non-metallic minerals. Major mineral is black granite production is about 10,254 tons. In most of the regions of Kollegal taluk, granite rocks were found and mining activities are seen. In the eastern region of this taluk, gneiss rocks were found and southern region is surrounded by M.M. Hills. B.R. Hill is one of the famous biodiversities and hill station in the world in Yelandur taluk, which is completely surrounded by gneiss rock.


  Materials and Methods Top


The radium concentration and radon exhalation rates from the soil and rock samples of some area of Chamaraja Nagar district, Karnataka India, have been measured using LR-115 Type-II solid state nuclear track detector (SSNTD), by employing can technique. [6],[9],[10],[11],[12],[13],[14],[15] Soil and rock samples were collected from different locations of Chamaraja Nagar District. These samples were crushed sieved, oven-dried and taken in a cylindrical plastic can of a known dimension of 10 cm height and 7 cm diameter. [6],[9],[16] LR-115 Type-II SSNTD was fixed inside surface of the lid of cylindrical can such that the sensitive part of the detector should face the specimen, contained in the cylindrical plastic can. Detector and specimen are sealed in a plastic can and allowed the specimen exposed to the detector for a period of 90 days. Thus, the sensitive part of the detector is exposed freely to the emergent radon from the samples in the can so that it could record the traces of alpha particles resulting from the decay of radon. [11],[12],[13],[14],[16] Activity of emergent radon can be calculated from the geometry of the can and time of exposure. After exposure, the detector were removed and etched in 2.5 N sodium hydroxide solution at 60°C for a period of 60 min in the etching bath. The effective radium concentration CR can be calculated using the formula mentioned below: [6],[9],[11],[12],[16]




  Results and Discussion Top


The results of radium concentration and radon exhalation rate in soil samples belonging to some areas of Chamaraja Nagar district, Karnataka state, India, are shown in [Table 1]. The radium activity in a soil sample varies from 3.6 to 34.1 Bq/kg, with an average value of 18.1 ± 9.8 (SD) Bq/kg. Mass exhalation rate of radon varies from 10.0 to 31.4 mBq/kg/h with an average value of 20.0 ± 7.4 mBq/kg/hand Surface exhalation rate of radon varies from 142.0 to 918.4 mBq/m 2 /h with an average of 439.9 ± 211.6 (SD) mBq/m 2 /h.
Table 1: Concentration of radium and exhalation rate of radon in soil samples

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The values of radium concentration in soil samples are found to be high at Kuderu (34.1 Bq/kg), Heggavadi (31.0 Bq/kg) and Kanakagiri Hill (27.3 Bq/kg). The average values of 226 Ra concentration reported for the normal background areas of Indian soil is 15 Bq/kg and the corresponding world average is 30 Bq/kg. [1],[15],[17] The effective radium content in sand samples of Kerala state varies from 45.6 to 226.1 Bq/kg. [18] Compared to these values concentration of radium in soil is lower in Chamaraja Nagar area. The surface exhalation rate of radon in soil samples is found to be high at Kanakagiri Hill-2 (918.4 mBq/m/h). Higher radon exhalation rate is mainly due to high radium concentration in the soil sample.

The radium activity in rock sample varies from 2.9 to 39.5 Bq/kg with an average value of 20.1 Bq/kg. Mass exhalation rate of radon in rock samples varies from 8.0 to 119.7 mBq/kg/h and surface exhalation rate of radon varies from 93.9 to 1787.3 mBq/m 2 /h respectively. The concentration of radium and exhalation rate of radon in rock samples is shown in [Table 2]. The concentration of 226 Ra in rock samples, in this region are low compare with the values observed in Bangalore region [3] and comparable with the values observed in Mysore region. [16]

The high radium concentration in rock sample is found at Suragi Hill and Santhemarahally village. The mass exhalation rate and surface exhalation rate in rock samples are found to be high at Kanakagiri Hill (37 mBq/kg and 1787.3 mBq/m 2 /h), Suragi Hill (119.7 mBq/kg and 1618.0 mBq/m 2 /h). The variation in exhalation rate of radon is due to nature of the samples, emanation factors of radon from them and diffusion coefficient of radon in different samples and radium content of the samples. [8],[9],[12],[15] Furthermore, the concentration of radium and radon depends on the type of rocks, geological formation of rocks, of the study area, stone cracks and due to breaking of bedrocks. The bed rocks have a high content of radium and when bedrocks gets destroyed and fissured radon gas can diffuse through the structure of bedrock and enhance the concentration of radium. [3],[6],[12]
Table 2: Concentration of radium and exhalation rate of radon in rock samples

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The predominant geological formations in the study area are granites. The higher concentration of radium in Kuderu and Heggavadi villages and at Kanakagiri Hill and Suragi Hill is due to the presence of granitic and gneiss type of rocks in these areas. The concentration of radium that governs number of radon atoms formed and emanate from the mineral sources. [8],[13],[16] The higher values of radium in soil samples can causes a significant increase in environmental radon in these areas.

Granites are major sources of radon due to the presence of a large amount of 238 U in its natural formation and hence exhalation rate of radon are higher in these regions. [14],[15],[19],[20] The major types of soil in these areas in the district are reddish brown forest soil, yellowish grey to grayish sandy loamy soils and mixed Soils. Red soil is present in upland areas and also noticed at the contact of granites and schist. The exposure of soil to stone dust containing high radium concentration also increases the activity of radium concentration in soil samples. The high permeability, porosity and grain structure is responsible for the exhalation rate of radon from the soil of the above mentioned area. [1],[13]

Kuderu and Heggavadi villages and Suragi Hill near Ramasamudra village are located in Chamaraja Nagara taluk, where gneiss and charnockite type of rocks are found. And Kanakagiri Hill is located in Gundlupet taluk, the entire taluk is comprised of gray to pink granitic and gneiss rocks. These granitic rocks are the significant sources of 238 U this may be contributing for the higher exhalation rate of radon in these areas. [15]


  Conclusion Top


The radium concentration and radon exhalation rates from the soil and rock samples of some area of Chamaraja Nagar District, Karnataka India, have been measured using LR-115 Type-II SSNTD. The radium activity in the soil sample varies from 3.6 to 34.1 Bq/kg, with an average value of 18.1 ± 9.8 (SD) Bq/kg. Mass exhalation rate of radon varies from 10.0 to 31.4 mBq/kg/h with an average value of 20.0 ± 7.4 mBq/kg/h and Surface exhalation rate of radon varies from 142.0 to 918.4 mBq/m 2 /h with an average of 439.9 ± 211.6 (SD) mBq/m 2 /h. The values of radium concentration in soil samples are found to be high at Kuderu (34.1 Bq/kg), Heggavadi (31.0 Bq/kg) and Kanakagiri Hill (27.3 Bq/kg). The concentration of 226 Ra in soil samples, in this region are low compare with the values observed in Bangalore and Mysore region.

 
  References Top

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    Tables

  [Table 1], [Table 2]


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Introduction
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