PROFILES AND DOWNWARD MIGRATION OF CS-134 AND RU-106 DEPOSITED ON ITALIAN SOILS AFTER THE CHERNOBYL ACCIDENT

After the Chernobyl accident, several radionuclides were deposited on the soil of the Piemonte Region in Italy. Contamination values were monitored and the initial vertical soil profiles of Cs-134 and Ru-106 were determined. For both radionuclides, more than 60% of the total activity remained in the upper 1-cm layer of soil during the first 7 mo after the accident. The time history of the soil profiles was studied over a period of 3 y in two Piedmontese localities. A compartmental model was also developed to describe downward migration of Cs-134 and Ru-106. The results indicated a low mobility for both radionuclides. The change in their vertical profiles may be described using a box model with a transfer constant of 0.2 y-1 for Cs-134 and 0.3 y-1 for Ru-106 between 1-cm-thick layers. A strong association between the soil fine fraction and the mobility of both radionuclides was also found.