7Be vertical distribution in Argentinean and Brazilian soils,

MUNIZ, M.; MEIGIKOS DOS ANJOS, R.; LOHAIZA F.; J. JURI AYUB; H. VELASCO; RIZZOTTO, M.

Sao Sebatiao

Congreso; XXXV Reunião de Trabalho sobre Física Nuclear no Brasil; 2012

Sociedade Brasileira de Fisica

7Be is a cosmogenic radionuclide produced by cosmic ray spallation of nitrogen and oxygen in the atmosphere. This radionuclide enters continuously to the ecosystems through wet and dry deposition, being wet deposition the principal mechanism for incorporation of 7Be to the surface soil. This radionuclide has been extensively used as a tracer for the study of several environmental processes. In the last years, its application for the evaluation of erosion and sedimentation phenomena has been increased. In a previous work the atmospheric input of 7Be through precipitations and soil deposition were assessed in two sites, nearby to Niteroi (Brazil) and San Luis (Argentina) cities. With the aim to explore the possibilities of applying this radionuclide to estimate erosion and sedimentation processes in these regions, the vertical distribution of 7Be on the soil profile was analyzed. The soil samples were collected using plastic tubes of  10 cm diameter. These tubes were driven into the soil and then, the soil profile was extracted without disturbance. In laboratory the soil profile was divided in layers of different depths. For each sampling time, 2 - 5 soil cylinders were taken, and the layers for a same deep interval homogenized, with the aim to obtain the mass sample needed to - spectrometry analysis. Soil samples were dried in stove (120 oC) to constant weigh, sieved through a 2 mm mesh and conditioned in Petri dish, for - spectrometry. For Brazilian soils the 7Be areal activity density ranged from 186  74 Bq m−2 to 727  290 Bq m−2 for the summer months; while for Argentinean soils ranged from 51  25 Bq m−2 to 438  114 Bq m−2 (annual cycle). The changes in 7Be soil content among months of the year could be explained by the asymmetric input from the atmosphere through precipitations. The vertical distribution of 7Be areal activity density on the soil profile was fitted to an exponential decreasing function. The results obtained for each site are comparatively discussed.