INFLUENCE OF PHYSICAL FACTORS ON RADIONUCLIDES CONTENTS IN SOILS FROMBISCAY (SPAIN)

The content of radioactive constituents in Biscay soils has been inves tigated in 15 cm cores, at three depth levels, for fourteen sampling p ositions. At the same time, each soil was characterized by physical pa rameters (depth level, geographical position, apparent density, and pa rticle, size distribution in clay+silt, fine sand and coarse sand frac tions). Radionuclides analyses were performed in Marinelli flasks with a gamma spectrometer (Ge-HP detector and 8000 channels analyser). Sev en natural radioisotopes (K-40, Ac-228, Bi-212, Tl-208, Ra-226, Pb-214 and Bi-209) and the artificial radiocaesium were identified and measu red. Relations among natural radionuclides and physical soil parameter s are mainly obtained by two statistical multivariate methods (linear multiple regression analysis and numerical taxonomy). Dependences of a ll radionuclides with apparent density and size fractions were found. Some specific relations with depth level (Cs-137, Bi-214 and Tl-208) a nd geographical position (K-40 because of the proximity to the sea) we re also detected. High relations were found among all natural radiosot opes, but a different behaviour is patent for the artificial radiocaes ium. Specific activities of size fractions of soils were determined fo r samples from two points, suggesting an accumulation of activity in t he clay+silt fraction.