Increase in the activity concentration of uranium 238 in agricultural soil by fertilization effect and its environmental implications

摘要

The gamma spectroscopy is used in this work for determining the activities of radioelements contained in fertilized soil samples. The evaluation of ~(238)U activity is based on measures around energy peaks 63.3 keV and 92.38 keV emitted by ~(234)Th which is the first product of the ~(238)U decay by radio emission. To confirm the results found, further evaluation of the activity of ~(238)U was based on measurements of emissions of its fifth descendant (~(226)Ra). In normal circumstances, the natural content of ~(238)U in sediment or soil is typically of the order of 40 Bq/kg. For the soil samples studied, while the activity of radium 226 is normal (between 40 and 53 Bq/kg), that of ~(238)U is five times higher for fertilized soils (up to 316 Bq/kg). This shows that it is an industrial source of uranium supply (fertilization effect) in soil samples and not a uranium traces accumulation contained naturally in the atmosphere. The radiological hazards of the radium equivalent activity (Ra_(eq)), representative level index I_(γr), external (H_(ex)) and internal (H_(in)) indices and annual effective dose due to the presence of these radionuclides in the investigated samples were calculated from the activities of ~(226)Ra and then compared with values estimated from ~(234)Th.