The ability of ionizing radiation to produce condensation nuclei aerosols in filtered air is well known. Recent studies have indicated that radiolysis results initially in the production of highly diffusive, nanometer-sized (<2 nm) clusters. Aerosols in the 1-10 nm range are also produced by other processes mostly involving nucleation, e.g. for purposes of materials synthesis. Radiolytic nuclei can be formed by the binary ion-induced nucleation of the precursor vapors, such as sulfuric acid and water; ultrafine particles (>5 nm) can then evolve by coagulation and growth processes. The nanometer nuclei are, however, poorly detected by condensation nuclei counters (CNCs) since CNC efficiencies drop sharply for particle sizes <5 nm. In this work, the formation of: (1) PoOx molecular cluster aerosols from the decay of radon, and (2) sulfuric acid nanometer nuclei and ultrafine aerosols from the radiolytic oxidation of SO2 in radon-air mixtures, were studied through wire screen-based size distribution measurements of the 218Po radioactivity associated with the aerosols. Comparisons with conventional diffusion battery-CNC derived number size distributions are also presented.