The concentrations of radionuclides belonging to the natural radioactive series, K-40 and Cs-137, were determined from radioactive precipitation. Many physical, chemical, and biological parameters influence the vertical distribution of radioactivity within soils. These factors include the nature and characteristics of the soil; the amount of rain deposited; surface layer disturbances; and other peculiar properties of the soil, such as the contents and types of clay minerals, organic matter, etc. For measurements of radionuclide concentrations, the high performance gamma spectrometry technique was used. Ten samples of each type of soil were collected, up to 50 cm depth, with samples obtained every 5 cm. Analyzes were carried out to determine, among other parameters, pH, clay content,+ , Na + , Ca ++ and Mg ++ and extractable acidity. Data were also obtained on local rainfall, temperature and relief, and related to latitude, longitude and altitude. It was observed that the higher concentrations of Cs-137 in Bmq -2, are found in the three most superficial samples of each profile. Over 60% of the concentration is confined to the top 25cm of all sampling sites. A high linear correlation was found between the concentrations of Cs-137 in the soil surface samples of each profile and the organic carbon content and, until 50 cm depth, the contents of Ac-228 and Tl-208, for the different samples of each soil profile analyzed did not vary substantially. These data contribute to show the state of relative radioactive equilibrium in the six soil profiles studied. It is observed, therefore, that these soils did not suffer erosion, and that the leaching process is not important for these elements belonging to the natural radioactive families.
