ALFA, BETA AND GAMMA MEASUREMENTS OF NATURAL OCCURRING RADIONUCLIDES AND ASSOCIATED DOSE RATES IN SOIL OF SOUTHERN ITALY

Since the Earth was formed, some chemical elements present in the environment are naturally radioactive. The terrestrial component of the natural background is related to the members of the radioactive decay chains of 232Th, 235U and 238U, along with 40K, which are present in variable quantities in the rocks forming the Earth's crust. Naturally occurring unstable radioactive elements are found in all rocks, soils and waters. The exposure to these cosmic and terrestrial sources cannot be avoided and everybody receives some radiation dose from this radioactivity. When a biological system comes exposed to an ionizing radiation field, it becomes the site of a series of chemical, physical and biological processes, originating from the transfer of energy by radiation, which can induce direct damage to tissue cells and there is no threshold below which can be said that the stochastic risk is zero. In this study, a, b and g radiation and their associated equivalent dose rate of natural radionuclides were estimated in 99 surface soils samples collected randomly from soils scattered on the Crati basin, in Calabria region (southern Italy), where a high climatic variability due to its position in the Mediterranean area occurs. A high sensitivity detector up within a Geiger-Muller tube and with an external probe NaI (Tl) was used for the survey. The mean equivalent dose rate for surface soils is 97.92 ?Sv/h, with a maximum value of 147 ?Sv/h and a minimum of 31 ?Sv/h. The mean value in soil samples was higher than the worldwide mean equivalent dose rate values reported by UNSCEAR, but the present result was not statistically significant to cause fatal cancer risk to population in the study area. These evidences can be ascribed to the presence of plutonic and metamorphic crystalline rocks in the Sila Massif, located to the east of the Crati basin, of crystalline rocks of the Coastal Chain to the west, and of carbonate and siliciclastic sedimentary rocks of the Pollino group to the north. Primary minerals constituting rocks which contain K, U, and Th, such as monazite, zircon, are responsible of the apparent activity of the radionuclides. In addition, peculiar soil properties and pedogenetic processes play a prominent role in radionuclide release from primary minerals and on their mobilization and/or retention in the soil system. This radioactivity survey represents a preliminary study to characterize the background levels of naturally occurring radionuclides in soil from the Crati basin (Calabria region, southern Italy) and thus to contribute improving world radioactivity database.