Studies on Radon at Mysore City, India

Humans are continuously exposed to ionizing radiation from natural sources. The main contributors to natural radiation are high-energy cosmic radiation and radioactive nuclides that originate in the earth’s crust. Rn, a decay product of Ra, originates from the naturally occurring U decay series. Rn, the only gas in the U decay series, is chemically inert, but is radioactive and exposure to it and its decay products constitutes about half the radiation dose received by general population. The quantity of radon that escapes from the earth depends mainly on the concentration of radium in the soil along with other factors, like the type of the soil cover, porosity, etc. With this in mind, a systematic study of radionuclide in samples of soil, rocks and water and also in ambient air was measured at about 500 locations in Mysore City, India. Radon, thoron and its progeny concentration in the atmosphere were determined using solid state nuclear track detectors (SSNTD), LR-115 type II which were placed inside the dosimeters and were suspended at a height of 2.5 m above the ground. The Gamma ray spectrometry method was employed to estimate the activity of Ra, Th and K in the soil and rock samples. Radon in the soil gas and radon exhalation rates from soil and building materials were also measured using SSNTDs. A gamma ray scintillometer was used to measure the gamma absorbed dose levels. Uranium analysis in water samples was performed using a laser flurometer. Radium and Radon concentration in water samples was measured using radon bubblers and scintillation cells. Analysis of the samples found that the concentration of Rn, Rn and their daughters in the atmosphere occurred higher during winter and lower during summer. The geometric median activity of Ra, Th and K in soil samples is found to be 20.3, 64.0 and 396.7 Bq kg; and rock samples was found to be 46.4, 68.7 and 634.9 Bq kg respectively. The average gamma absorbed dose rate in dwellings varies from 46.2 to 286.5 nGy h. Radon exhalation rates varied from 8.3 to 196.3 mBq m h in different types of soil and rock samples. The Rn and Uranium concentrations in water samples were found to vary from 280 to 794,170 Bq L . and from 0.3 to 635.4 μg L respectively.