Indian Journal of Pure & Applied Physics Vol. 48, July 2010, pp. 527-529

Natural radioactivity in and Taluks of coastal

Gerald Pinto †, N Karunakara +*, H M Somashekarappa +, Chetan Rao +, Ujwal Prabhu + & I Yashodhara + +University Science Instrumentation Centre, University,Mangalagangotri 574 199, †Willagress College, Kallayanapura, Udupi, India *E-mail: [email protected] Received 22 April 2010; accepted 3 June 2010 The gamma radiation levels, 226 Ra, 232 Th and 40 K concentrations in soils of Udupi and Karkala Taluks of coastal Karnataka region of India have been studied in the present paper. The gamma absorbed dose rates were measured using portable GM survey meter. The soil radioactivity was measured by gamma spectrometry method using an HPGe detector. The results show that the 226 Ra concentration varies in the range 2.6-78.0 Bq kg −1 with a mean of 34.4 Bq kg −1, 232 Th in the range 2.3-166.2 Bq kg −1 with a mean of 45.3 Bq kg -1 and 40 K in the range 72.9-493.5 Bq kg −1 with a mean of 198.6 Bq kg −1 in the 0-5 cm soil profile. The gamma absorbed dose rates, measured using the GM survey meter, show that the dose varies in the range 70.0-123.0 nGy h −1. The regression analyses performed between the measured dose rates and that calculated from the primordial radionuclide activities show a poor correlation between the measured and calculated dose. Keywords : Radioactivity, Gamma radiation levels, Radionuclide

1 Introduction Ltd., Hyderabad, India). Soil samples were collected The two prominent sources of external radiations from 0-5 cm profile from 29 sampling station. Samples are cosmic rays and terrestrial gamma rays. Terrestrial were processed and concentrations of 226 Ra, 232 Th and gamma rays derive essentially from 40 K and the 40 K were determined by gamma spectrometry using a 238 232 radionuclides belonging to U and Th series that HPGe detector (41% efficiency n-type detector, are present in earth’s crust. Apart from these natural Canberra, USA) coupled to a DSA-1000 with 16K sources, modern scientific and technological activities MCA. The detector was enclosed in a 10 cm thick also contribute to the radiation level in the graded lead shield (Model 747, Canberra, USA). The environment, which would be significant if proper 226 Ra activity was evaluated from the weighted mean precautions are not taken. Therefore, studies aimed at of the activities of three photopeaks of 214 Bi (609.3, establishing the baseline data on radiation levels and 1129.3 and 1764.5 keV) after subtracting the radionuclides distribution in various environmental background counts and applying Compton matrices of a region is important because such a study corrections. In the case of 232 Th, one photopeak of would help to assess, in future, the impact of our 228 208 Ac (911.2 keV) and two photopeaks of Tl (583.1 scientific and technological activities on the and 2614.5 keV) were used in the same way. The environment. Hence, detailed studies were carried on activity of 40 K was derived from the 1460.8 keV the background radiation levels and natural radionuclides concentration in soils of Udupi and gamma line of this isotope. The detector efficiency Karkala taluks of Coastal Karnataka region of India. calibration was performed using the IAEA quality The region, known for its splendidly beautiful assurance reference materials: RG U-238, RG Th- environment, is now witnessing a rapid 232, RG K-1 and SOIL-6. The Minimum Detection industrialisation with setting up of many major Levels (MDL) for the gamma spectrometer system used in the present study were 0.2, 0.3 and 1.2 Bq industries including Thermal Power Stations. The − results of gamma radiation levels and 226 Ra, 232 Th and kg 1 for 226 Ra, 232 Th and 40 K, respectively for a 40 K activities in the soil are presented in the paper. counting time of 60,000 s and a sample weight of 0.3 kg. Details of the measurements technique were 2 Experimental Details published 1. The external gamma dose rates in air were measured in different locations of the study area using 3 Results and Discussion a portable GM tube based Environmental Radiation Radionuclides distribution in soil — The results of Dosimeter (model ER709, Nucleonix Systems Pvt. measurement of 226 Ra, 232 Th and 40 K activities in 528 INDIAN J PURE & APPL PHYS, VOL 48, JULY 2010

surface soils of Udupi and Karkala Taluks are the entire study region with results of individual presented in Table 1. The overall range and mean locations fluctuating around the mean value. The values for the entire study region are also presented in mean value of dose rates prevailing in south west Table 1. The activity of 226 Ra is in the range 2.6-78.0 coast of India is comparable to the mean values of Bq kg −1 with a mean value of 34.4 Bq kg −1, 232 Th in 80.7 nGy h −−−1 and 88.7 nGy h −−−1 repoted by others 5,6 for the range 2.3-166.2 Bq kg −1 with a mean value of different regions of India. The dose rates are also −−− 45.3 Bq kg −1 and that of 40 K in the range 72.9- comparable with the world range 28-120 nGy h 1 and −−− 493.5 Bq kg −1 with a mean value of 198.6 Bq kg −1 in the average value 56 nGy h 1 reported for normal the surface (0-5cm) soils. These values are background areas 4. comparable to those reported for other normal From the results of 226 Ra, 232 Th and 40 K activities in background regions of India 2 and the world 3, 4 . soil the gamma dose rates in air were calculated using Gamma absorbed dose rates — The results of the dose coefficients 7 (nGy h −−−1 per Bq kg −−−1) 0.462, gamma absorbed dose rates in air measured using the 0.604 and 0.0417 for 226 Ra sub-series, 232 Th series and GM survey meter, which includes both terrestrial and 40 K, respectively and by assuming secular equilibrium cosmic ray components, are presented in column 7 of between 238 U and 226 Ra. The results of these Table 1. The absorbed dose rates vary from calculations are summarized in column 6 of Table 1. 70-123 nGy h−−−1, with a mean value of 97 nGy h −−−1. The It may be noted that calculated dose rates does not dose rates were found to be more or less uniform in include the cosmic ray component. The dose Table 1 — Radionuclides concentration in soil and gamma absorbed dose rates

Region Place Activity of radionuclides (Bq kg −1) Gamma Absorbed dose rates (nGy h −1) 226 Ra 232 Th 40 K Calculated * Measured

Udupi Kodavoor 34.9±0.9 26±1.0 73.0±4.1 35 79 Taluk Cherkady 26.1±0.9 44.9±1.2 219.2±6.6 48 79 Kakkunje 42.9±1.1 43.6±1.3 128.8±6.0 52 105 Karje 6.1±0.7 14.8±0.8 493.5±10.1 32 105 Kukke Halli 19.7±0.7 24.8±0.9 108.6±4.6 29 105 Dupadakatte 44.2±1.0 51.7±1.3 124.5±5.4 57 88 Kemmannu 12.83±0.7 18.9±0.9 366.5±8.5 33 96 Barhmavar Sugar Factory 29.4±0.8 25.28±0.9 89.9±4.3 33 88 54.8±1.1 49.9±1.2 190.5±6.4 63 105 Pamboor 34.7±0.9 41.3±1.2 199.5±6.4 49 114 Shivally 55.1±1.1 38.9±1.1 183.8±6.1 57 123 Nejar 63.5±1.1 51.4±1.3 194.8±6.5 69 96 Tenkanidiyur 17.9±0.8 26.9±0.9 222.6±8.2 34 79 Hebri (Near Karje) 48.6±1.2 79.3±1.7 202.3±8.3 79 70 Yedthady 21.4±0.8 21.3±0.9 137.0±5.2 28 114 Kukkehalli North 23.0±0.7 28.1±0.9 119.7±4.7 33 123 Kokkarne 15.1±0.6 29.3±0.8 72.9±3.7 28 105 Hebri Nisargadama 30.8±0.9 47.2±1.2 254.1±7.0 53 105 Perampalli 48.9±1.0 40.7±1.2 92.8±4.9 51 123 Herror 43.5±0.8 27.0±0.8 105.1±4.2 41 88 Cherkady 26.2±1.0 53.4±1.4 256.6±7.8 55 79 Sand 2.6±0.4 2.31±0.5 231.7±6.3 12 70 Hoode sand 41.1±1.0 88.8±1.6 84.3±4.7 76 70 Nandikoor 21.8±1.0 6.9±1.6 171.1±6.7 21 88

Karkala Nakre 38.9±1.0 118.9±1.8 213.9±6.6 99 114 Taluk Ajekar 78.0±1.4 166.2±2.2 323.1±8.6 150 112 Karkala 53.9±1.3 60.9±1.3 230.6±7.1 71 114 Bailur 33.8±1.0 47.0±1.2 477.1±10.3 64 114 Nitte 28.4±0.9 37.1±1.1 190.6±6.6 43 70

Range 2.6-78.0 2.3-166.2 72.9-493.5 12-150 70-123 Mean 34.4 45.3 198.6 52 97 SD 17.4 33.6 107.6 27 18

*Total gamma dose calculated from the activities of 226 Ra, 232 Th and 40 K. This does not include cosmic ray component

PINTO et al .: NATURAL RADIOACTIVITY IN KARNATAKA 529

delivered by these radionuclides, in total, range from reported for other normal background regions of India 12 to 150 nGy h −−−1 with a mean value of 52 nGy h −−−1. and the world. This value of total absorbed dose rate is comparable with the reported 3 world average value of 44.4 nGy Acknowledgement h−−−1. The regression analyses performed between the The authors are thankful to University Grants measured dose rates and that calculated from the Commission (UGC), New Delhi for sponsoring the primordial radionuclide activities did not show a good research project to undertake this study. correlation between the measured and calculated dose References with regression equation being Y=0.3X+22.1 (where 1 Karunakara N, Somashekarappa H M, Narayana Y, Avadhani Y is the measured dose with GM survey meter and D N, Mahesh H M & Siddappa K. Health Phys , 80 (5) (2001). X is the dose calculated from the measured 2 Kamath R R, Menon M R, Shukla V K, Sadasivan S & Nambi concentrations of 226 Ra, 232 Th and 40 K in soil) with K S V, In : Fifth National Symposium on Environment (Sastry, R=0.2 for n=29. V N, Bapat, V N and Desai, M V M, Eds ), VECC and SINP, Calcutta, India, Feb 28-March 1, (1996) 56. 3 United Nations Scientific Committee on the Effects of Atomic 4 Conclusions Radiation ( UNSCEAR ) Sources, Effects and Risks of ionising The study has established the baseline data on radiation, Report to the General Assembly (United Nations, New 226 Ra, 232 Th and 40 K in the soils of Udupi and Karkala York), (1988). 4 United Nations Scientific Committee on the Effects of Atomic Taluks. The database would help in assessing, in Radiation (UNSCEAR) Forty-second session of UNSCEAR future, the environmental impact of operation of A/AC 82/R 526 United Nations, New York, (1993) major industries, including thermal power stations 5 Mishra U C & Sadasivan S, Health Phys, (1971). that are coming up in the region. The activities of 6 Nambi, K S V; Bapat, V N; David, M; Sundaram V K; Sunta these radionuclides in soil and the gamma absorbed C M; Soman S D HPD, BARC, India, (1986). 7 United Nations Scientific Committee on the Effects of Atomic dose delivered by these radionuclides to the Radiation (UNSCEAR). Annex B. Exposures from natural population of the region are comparable to those radiation sources,. (2000) 84-156.