The Adsorption of Radon Daughters to Some Polydisperse Submicron Polystyrene Aerosols

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Abstract
The adsorption of radioactive materials to aerosols is an important consideration when assessing the hazard associated with the inhalation of radioactive materials. The adsorption of radon daughters to aerosols is of particular interest since it is probable that radon daughters attached to aerosols represent the primary hazard in uranium mining. In this investigation, the adsorption of radon daughters to polydisperse aerosols of polystyrene spheres in the diameter range from 0.04 to 0.5 μ was studied. Electron micrographs were used to characterize the aerosols. The Goetz Aerosol Spectrometer was employed with a new analysis method to relate the quantity of adsorbed radon daughters to aerosol particle size, after radon gas in concentrations around 2 × 10-8 Ci/l. interacted with aerosols in concentrations of about 104 particles/cc. The results showed that the relative quantity of adsorbed radon daughters on different size aerosol particles up to 0.5 μ in diameter was proportional to the surface area of the particles. A theoretical explanation of this phenomenon is developed which suggests that this effect is caused because the Brownian motion of the aerosol particles cannot be ignored even though their diffusion coefficients are relatively small and that the diffusion relationships for highly diffusable materials interacting with aerosols only apply for very high interaction rates. For low interaction rates the dynamical character of aerosols favors random surface interactions rather than diffusion gradients. This explanation implies that the adsorption of radon daughters is proportional to particle surface area for all aerosol particle sizes and for all but extremely high concentrations of radon gas.