No abstract

Human beings are exposed to background radiation that stems both from natural and manmade sources. Natural background radiation, which is equivalent to 2.4 mSv per person, makes up approximately 80% of the total radiation dose a person is exposed in a year (1). Soil radionuclide activity concentration is one of the main determinants of the natural background radiation. Volcanic geographic structures as well as rocks that are rich in phosphate, granite and salt contain natural radionuclides like 238 U, 232 Th and 40 K. When rocks are disintegrated through natural processes, radionuclides are carried to the soil by rain and .lows (2). The natural radioactivity in soil comes from 226 Ra, 232 Th and from natural 40 K. Some other terrestrial radionuclides, including those of the 235 U series, 87 Rb, 138 La, 147 Sm and 176 Lu exist in nature but at such low levels that their contributions to the dose in the humans are small. Arti.icial radionuclides can also be present such as 137 Cs, resulting from fallout from weapons testing. 137 Cs is a .ission product which is formed through nuclear tests and accidents. The deposition of 137 Cs in soil is important since its half-life is 30.2 years and it has a gamma emission of 661 keV (3). The radiological

No abstract