[Areal concentration and vertical migration of Cs-137 in some soils of the ninth and tenth region]
1992
Llanca G, Ardriana Olga
At nine sites located in the 9th and 10th Region of Chile, areal concentration and vertical migration of Cs-137 were determined on uncultivated soils for the past thirty years. Samples were collected at selected places from 1989 through to 1990 in 1-10 cm depth increments from the walls of a pit. Cs-137 concentration was determined by high resolution gamma spectrometry with a HP Ge detector in samples of 500 cm3. Physico-chemical soil characteristics were determined by traditional methods. The Cs-137 areal concentration determined ranged from 700 to 2440 Bq m-2, surpassing as much as three times the values estimated in previous reports for the cumulative deposit of the above mentioned radionuclide at the corresponding latitude. The Cs-137 cumulative areal concentration decreases exponentially with depth for unlabored soils. The Cs-137 migration at the soil profiles can be measured by the relaxation coefficient, defined as the depth at which the cumulative areal concentration decreases to 37%. There exists a significative positive correlation between the relaxation coefficient and the sand-silt fraction. As no Cs-134 traces were detected in the analyzed soils, it was established that the studied areas were not affected by deposition of radionuclides emitted during the Chernobyl nuclear accident. The maximum annual dose, 1 m from the soil surface, by effect of the measured Cs-137 areal concentration, is about 1 to 2% of the annual human dose
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