Experimental study of ionhyphen;induced nucleation by radon decay

摘要

In the environment, the presence of ions from natural radioactivity may increase the rate of new particle formation through ionhyphen;induced nucleation. A thermal diffusion cloud chamber (TDCC) has been built to experimentally study ionhyphen;induced nucleation where the ions are produced by gaseous radioactive sources. The critical supersaturation values and nucleation rates for methanol, ethanol, 1hyphen;propanol, and 1hyphen;butanol vapors on ions produced within the volume of the chamber by alpha decay of222Rn have been measured quantitatively at various radioactivity concentrations and supersaturations. The presence of ion tracks and the effect of an external electric field were also investigated. The alpha tracks and ionhyphen;induced nucleation formed by222Rn decay become visible at the critical supersaturation that is below the value needed for homogeneous nucleation. At this supersaturation, the nucleation rates increase substantially with increasing222Rn at low activity concentrations, but attain limiting values at higher concentrations. The experimental results indicate that the ionization by radon decay will promote ionhyphen;cluster formation and lower the free energy barriers. The formation of visible droplets is strongly dependent on the supersaturation. This study also confirms that the external electric field has a significant effect on the observed rates of nucleation.