Estimation of Po in Coastal Regions of Kannyakumari District of Tamil
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International Journal of Pure and Applied Physics. ISSN 0973-1776 Volume 7, Number 3 (2011), pp. 229-234 © Research India Publications http://www.ripublication.com/ijpap.htm Estimation of 210Po in Coastal Regions of Kannyakumari District of Tamil Nadu, India V. Sarojini1, K. Esaiselvan2, K. Sreekumar3 and T. Chithambra Thanu4 1Asst. Prof. Dept. of Physics, Lekshmipuram College of Arts and Science, Neyyoor-629802, Tamil Nadu, India E-mail:[email protected] 2Chemist, Indian Rare Earths Limited, Manavalakurichy, Tamil Nadu, India E-mail: [email protected] 3Scientific Officer, Health Physics Unit, Indian Rare Earths Limited, Manavalakurichy, Tamil Nadu, India E-mail: [email protected] 4Associate Prof. Dept of Physics, S.T. Hindu College, Nagercoil, Tamil Nadu, India E-mail: [email protected] Abstract The coastal regions of Kanyakumari district, Tamil Nadu in India between Midalam to Muttom stretch is witnessed as a naturally high back ground radiation area. Soil samples from the beach area were analysed for 210Po activity. The activity concentration of 210Po was measured by chemical deposition method in the beach soils along the coastal stretch from Muttom to Midalam. These studies were carried out from April 2010 to May 2010 in the Health Physics Unit of BARC located in the campus of Indian Rare Earths Limited, Manavalakurichy in Tamil Nadu. The activity of 210Po in the beach soil were found to be varying from 11.32 Bq/Kg to 54.53 Bq/kg. The maximum 210Po activity was found to be 54.53 Bq/Kg estimated at Chinnavilai and the minimum 210Po activity was found to be 11.32 Bq/Kg estimated at Colachel. The results of these studies are presented and discussed in this paper in detail. Keywords: Polonium activity, Chemical deposition method, beach sands. 230 V. Sarojini et al Introduction Radioactivity is the process of spontaneous emission of certain invisible radiation from nucleus which can ionize the atom. Radiation is the energy traveling in form of particles or waves in bundles of energy called photons. It is a process in which the nuclei of certain elements undergo spontaneous disintegration emitting active radiation. The elements which undergo spontaneous decay are called radioactive elements. Radioactivity present in the soil is mainly due to the presence of radioactive elements in the earths crust. Southwest coastal region in Tamil Nadu, India has been reported as high radiation area1 due to the existence of these elements. The radioactivity concentration of 210Po was measured by chemical deposition method2 in the beach soils along the coastal stretch from Muttom to Midalam, K.K district of Tamil Nadu in India. Polonium is a radioactive element that occurs naturally in very low concentration in the earth’s crust3. Although it can be produced by the chemical processing of Uranium ores or minerals. Uranium ores contain less than 0.1 mg 210Po per ton. As 210Po is produced from the decay of 222 Rn gas, it can be found in the atmosphere from which it is deposited on the earth’s surface. Although direct root uptake by plants is generally small, 210Po can be deposited on broad leaf vegetables. Deposition from the atmosphere on tobacco leaves results in elevated concentrations of 210Po in tobacco smoke4. 210Po is a radioactive decay product in the natural Uranium-238 decay series along with lead-210. 210Po has a half life of 138 days and it decays to stable lead-206 by emitting an alpha particle. The energy released by its decay is so large (140 w/g) that a capsule containing about half a gram reaches a temperature above 5000C. 210Po is highly radioactive and chemically toxic element. Direct damage occurs from energy absorption into tissues from alpha particles. As an alpha emitter 210Po represents a radiation hazard only if taken into the body. One of the prime sources of high background radiation level is the presence of radioactive monazite. Monazite sands are known to contain thorium, with some amount of 238U and 40K 5. The existence of monazite deposits in coastal areas of K.K. district and Kerala have been reported by several investigators. One of the regions where high radiation level has been reported is coastal areas of Muttom to Midalam in Kanyakumari district of Tamil Nadu, India. 210Po is a daughter product of 238U and is found in varying concentration in soil. Therefore an attempt is made in the present investigation to studies on the estimation of 210Po activity in the beach soils of coastal regions in K.K. district of Tamil Nadu, India. Materials and Methods Study Area and Sample Collection The study area is mainly the coastal stretch between Muttom to Midalam, in KK district of TamilNadu, India. The beach soils were collected from ten major sites namely Muttom, Kadiapattinam, Chinnavilai, Periyavilai, Puthoor, Kottilpad, Colachel, Simon colony, Kodimunai and Vaniakudi. The samples were collected in a polythene bag and brought to the laboratory. Estimation of 210Po in Coastal Regions of Kannyakumari District 231 Figure 1: Map of the Sampling Stations. Sample processing and Activity determination The chemical deposition method was employed for the determination of 210Po activity. The soil samples were dried in an oven at 1100C till a constant dry weight is obtained. About 3gms of samples were leached with 4N HNO3 and then organic matter present in the sample was destroyed by digestion by adding HNO3 + H2O2 mixture in a small increments to get a white residue. To the dried precipitate 20ml of 1:1 hydrochloric acid is added and heated to dryness. The precipitate was then dissolved in 0.5N hydrochloric acid and the solution is then ready for plating. A silver disc whose alpha count was previously determined is taken and concentration of 210Po in the sample was deposited into the silver disc by stirring it at 970C for 6 hrs with the help of a magnetic stirrer. The silver disc was then washed with distilled water and dried under an IR lamp. The silver disc was then counted on both the sides for α activity using Zns (Ag) detector for 2000 seconds. Results and discussion: The 210Po activity concentration in soil samples of different locations is given in table1. The activity was found to be varying from 11.32 Bq/Kg to 54.53 Bq/Kg. The highest 210Po activity was found in Chinnavilai and this may be due to higher monazite concentration in the soil of this area. The lowest activity was determined at Colachel. This may be due to low percentage of clay and organic matter in the soils of this region. Moreover in soil polonium also comes from the atmospheric precipitation due to decay of 222Rn present in the atmosphere in addition to the decay of 238U present in the soil. 232 V. Sarojini et al Table 1: Activity of 210 Po. No Sampling Station Activity of 210Po in Bq/Kg 1. Muttom 53.66 2. Kadiapattinam 41.04 3. Chinnavilai 54.53 4. Periyavilai 47.06 5. Puthoor 20.98 6. Kottilpad 14.33 7. Colachel 11.32 8. Simon Colony 37.87 9. Kodimunai 39.98 10. Vaniakudi 44.20 Figure 2: Variation of 210Po activity. Conclusion From the above analysis it is evident that the concentration of 210Po activity was higher at Chinnavilai (54.53 Bq/Kg) and the lower concentration of 210Po activity was reported at Colachel (11.32Bq/Kg). The presence of heavy minerals like ilmenite, rutile, garnet, Zircon, monazite, in the beach sands of coastal Kanyakumari district are the major contributions of radioactivity in this area. 232Th and 238U are reported from these regions, caused mainly due to the monazite bearing black sands. The presence of 210Po in surface of soil is due to the deposition from atmosphere, leaching from soil Estimation of 210Po in Coastal Regions of Kannyakumari District 233 and rock courses formed from dissolved 226Ra and 222Rn. The surface soil activity of 210 Po depends on the clay and organic matter of the soil. List of symbols and abbreviations Symbols Abbreviations 1. 210 Po – Polonium 210 BARC – Babha Atomic Research Centre 2. Bq/Kg – Becquerl per Kilogram K.K.Dist. – Kannyakumari District 3. 238U - Uranium 238 IR – Infra Red 40 4. K - Potassium 40 5. HNO3 - Nitric Acid 6. H2O2 - Hydrogen peroxide 7. α – Alpha 8. ZnS - Zinc sulphide 9. 222Rn – Radon 222 10. 232Th – Thorium 232 11. ml – Milli litre 12. W/g – Watt per gram References [1] Khanna D., Malathi J., Brahmanandhan, G.M.., and Selvasekarapandian, S., 2004. Measurment of Activity concentrations of 40K, 238U and 232Th in Soil samples of Agastheeswaram Taluk, Kanya kumari Dist, India., Paper presented in the Sixth Int.Conf. on High level Radiation Areas, Japan, September 5-9, 2004. [2] Iyengar M.A.R, Ganapathy, Kannan, Rajan S.V, Rajan M.P, Rajaram S, (1990) procedure manual workshop on Environmental Radioactivity held at Kaiga, India. [3] Pujol li., Sanchez- Cabeza, J.A., 2000. Natural and Artificial radioactivity in surface waters of the Ebo river basin (Northeast spain).Journal of Environmental Radioactivity 51, pp.181-210. [4] Carvalho F.P., 1995. 210Po and 210Pb intake by the Portuguese population: The contribution of Sea food in the dietary intake of 210Po and 210 Pb. Health Physics. 69(4). pp. 469-480. [5] Aswathanarayana U., 1964. 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