Adsorption of radioactive I2 gas onto fly-ash aerosol

The adsorption of radioactive elemental iodine (I2) gas onto fly-ash aerosol has been studied to provide basic data for the realistic and precise assessment of dose to the general public from radioiodine released from nuclear facilities. A mixture of fly-ash aerosol and 131I2 gas was passed through a cylindrical glass vessel so that particulate iodine was formed by adsorption of I2 onto aerosol. Then the concentrations of I2 and particulate iodine were measured. It was found that the adsorption reached an equilibrium state between 5 and 12 min and that the proportion of iodine which was adsorbed on the aerosol decreased with increasing initial I2 concentration ranging over 10-13 to 10-9g/cm3. The adsorption isotherm of the aerosol for I2 gas approximately followed Freundlich isotherm. Using the adsorption isotherm, a theoretical equation was derived to explain the adsorption on the basis of FUCHS' theory on the evaporation of droplets. A sticking probability in the equation decreased with increasing adsorbed amount. The calculated results were in good agreement with the experimental ones. (author)