40K, 137Cs and 226Ra Soil and Plants Content In Seminatural Grasslands in Central Argentina

JURI AYUB, J.; VELASCO, R. H.; RIZZOTTO, M.; QUINTANA, E. E.; AGUIAR, J. C.

AIP CONFERENCE PROCEEDINGS

American Institute of Physics

Año: 2008 p. 273 - 276

0094-243X

Activity concentrations of 40K, 226Ra and 137Cs have been analyzed in soil and plant samples, collected in permanent grassland in central Argentina. Two near areas (A1 and A2) under field conditions with soil undisturbed at least in the last four decades were selected. For each of the three studied radionuclides we do not find differences in the inventories between both areas. The inventories range from 143 kBq m-2 to 197 kBq m-2 for 40K and from 13 kBq m-2 to 18 kBq m-2 for 226Ra. The vertical distributions of 40K and 226Ra are uniform through de soil profile. For 137Cs the inventories range from 0.33 kBq m-2 to 0.73 kBq m-2. In spite of 137Cs inventories are similar in both areas the distribution through vertical profile is different. 137Cs activity concentration has a maximum for layers 5-10 cm depth in A1 and 10-15 cm depth in A2. For deeper layers both areas show similar activity concentrations. The diffusion coefficient (Ds) and convection velocity (vs) are estimated with a convection-diffusion model. Ds values are in the range reported in the bibliography, while vs values are one order of magnitude higher. After 40 years most 137Cs fallout is still in the layer 10-15 cm depth. The great penetration of 137Cs (25 cm) in these soils may be the result of a high sand and low fine materials content. 137Cs and 226Ra were not detected in grass samples. Activity concentration of 40K in vegetal samples ranges from 116 Bq kg-1 to 613 Bq kg-1. The TF values obtained for 40K show a lognormal distribution and ranges from 0.05 to 0.42.