The Distribution Behavior of Stable and Radioactive Cs between the Clastic Grains and Water in the Isolated Undisturbed Mountain Pond

The concentrations of stable Cs and radioactive fallout ^<137>Cs were determined for the clastic grain of the isolated undisturbed pond "Yasha-ga-Ike", located at an elevation of 1100m near the ridge of mountain in Fukui Pref. The concentrations of both cesiums varied with particle size and increased with a decrease in diameter. Using the concentration data for the pond water, the in-situ distribution coefficient Kd defined by the ratio of the element concentration adsorbed on the particle to that of the water was obtained both for the stable Cs of eight samples, taken at different times from June 1999 to October 2001, and the radioactive ^<137>Cs of four samples. The values of Kd increased with a decrease in particle diameter and ranged from about 10 to 1000m^3/kg, and the Kd for the stable Cs were slightly larger than those of ^<137>Cs. The results suggest that the adsorption of the stable Cs was established before the fallout of the ^<137>Cs, and the isotopic exchange between both cesiums has been proceeding from the water to the adsorbed layer and the grain matrix