An estimate of migration of 137Cs in a vermiculite column by measuring the surface dose rate with TLD

The surface dose rate of the vermiculite column was measured during about two years with TLD to predict the migration of 137Cs in the adsorbent layer. The vertical distribution of the surface dose rate was obtained from the data measured at intervals of five centimeter in vertical direction. From this dose rate distribution we estimated the length of the 137Cs adsorbed layer and calculated Kf value and distribution coefficient Kd of 137Cs using Inoue's method. And we calculated the surface dose rate of the vermiculite column considering the 137Cs adsorbed layer as a volume source of a uniform activity distribution. For this calculation, we simplified the shape of the vermiculite column to triple layer cylinder. The core of this cylinder is vermiculite which is surrounded with rubber and mild steel shells. Broder's equation is used to calculate a build-up factor for multi-layer materials. The result of this calculation shows good agreement with the measured values with TLD, thus we can estimate the migration of 137Cs in a vermiculite column by measuring the surface dose rate with TLD. (author)