Radionuclídeos naturais e artificiais em seis perfis de solos do estado do Rio Grande do Sul

Abstract

Concentrations of natural radioactive series radionuclides, of K-40, and of radioactive fallout Cs-137 are determined. Many physical, chemical and biological parameters influence the radioactivity vertical distribution in soils. Among these factors are soil type and characteristics; rainfall; superficial layers perturbations and other peculiar properties of the soil such as concentration and types of clay mineral, organic matter, etc. High performance gamma-ray spectrometry is used to determine radionuclide concentrations. Ten samples of each type of soil are collected, down to 50 cm with samples collected every 5 cm. pH, clay concentration, organic carbon and K+, Na +, Ca++ and Mg++ cations and total acidity are analyzed, among other parameters. Data on local pluviometry, temperatures and relief, latitude, longitude and altitude are also collected. It is observed that the highest concentrations of Cs-137 are found in the three uppermost superficial samples for every profile. More than 60% of the Cs-137 lays within the 25 cm uppermost layer for all sampling locations. It is observed for soil superficial samples of every profile, a high linear correlation between Cs-137 concentration and organic carbon concentration and that, down to a depth of 50 cm, Ac-228 and TI-208 concentrations do not vary appreciably for different equivalent samples. These results help showing the state of relative equilibrium within the six profiles studied. So it may be observed that these soils have not suffered from erosion and that lixiviation process is not important for these elements which belong to natural radioactive series.