THE RESUSPENSION AND REDEPOSITION OF CS-137 IN AN URBAN AREA - THE EXPERIENCE AFTER THE GOIANIA ACCIDENT

In Goiania, Brazil, the accidental opening of a Cs-137 teletherapy sou rce led to the contamination of an urban area of approximately 1 km2. The restricted, local contamination patterns without any significant i nfluence from previous contaminations (Chernobyl reactor accident and atmospheric atomic bomb test fall-out) provided a unique opportunity t o study the resuspension and redeposition mechanisms in an urban area under tropical climate characteristics. Air, total deposition, rainwat er, surface soil and street dust were sampled over 2 years at a garden of a house and the surroundings and analysed for Cs-137. The local me teorological conditions were recorded. In addition, some size fraction ation measurements were performed. The data show a significant seasona lity and a very slow long-term decrease with time for the activity con centration in air and deposition rate. Resuspension factors in the ord er of 10(-8) to 10(-9) m-1 (based on the air activity data) were deriv ed. A wide range of values for nominal deposition velocities were foun d, averaging at 5-6 cm s-1. Impactor measurements indicate that about 30-60% of the total particulate matter in air is due to aerosol partic les above 15 mum diameter. The data as a whole suggest that in Goiania resuspension and deposition are mainly local phenomena and no evidenc e was found for a significant spreading of Cs-137 from the place of pr imary contamination.