(730i) Aggregation Characteristics of Radioactive Particles in the Atmosphere

Understanding the microphysics of radioactive components in air is important for the accurate prediction of radioactivity transport in the environment. Aggregation and deposition rates of radioactive particles depend mainly on surface forces. Radioactivity can modify the surface charge of the transport media (e.g., aerosol particles); however, radioactivity-induced charging and its effects on radioactivity transport are currently not considered in predictive atmospheric transport models. In this study, the mechanisms of radioactivity-induced charging and its influence on aggregation kinetics of radioactive particles are investigated. Radioactivity-induced charging has been investigated by using scanning surface potential microscopy. Radioactive particles can be charged through self-charging and diffusion charging mechanisms, and the radioactivity-induced surface charge can be heterogeneously distributed due to the coupled effects of the charging mechanisms. Modeling based on particle collision probabilities has been carried out to analyze the interaction between radioactive particles (e.g., ¹³⁷Cs and Cs¹³¹I particles; ¹³⁷Cs and nonradioactive particles), modified by the heterogeneous charge distribution. Simulation results have indicated that radioactivity-induced charging hinders aggregation of highly radioactive particles, but facilitates aggregation between radioactive and nonradioactive particles. The influence of environmental parameters on radioactivity-induced charging and aggregation of radioactive particles are investigated.