THE CHARGING OF RADIOACTIVE AEROSOLS

The processes whereby radioactive aerosols become charged are examined and their rates are specified in terms of the amount and type of radioactivity present. General equations are obtained for the aerosol charge distribution and ion concentrations. Mean charges found from calculated distributions agree well with more approximate equations used previously by Reed et al. (1977, J. Aerosol Sci. 8, 457-463). The steady-state charge distribution for a monodisperse beta-decaying aerosol reduces to an analytic form, and gives a simple result for the mean charge when ion concentrations and mobilities are equal. Mean aerosol charges are found to be large when ion-ion recombination is the dominant ion removal mechanism, and when the aerosol is larger than a critical size. This size is only weakly dependent on the total aerosol mass concentration. Calculations are performed for a beta-decaying Au-198 aerosol and an alpha-decaying (PuO2)-Pu-238 aerosol, and reasonable agreement is obtained with experiment.