Mobility Spectra of Radon Daughter Aerosols Stored in a Vessel

The time variation in the mobility spectrum of radioactive charged particles, stored in a closed vessel, and the concentration ratio of positive to negative particles were studied by using a mobility spectrometer of parallel plates type. A remarkable variation in the mobility spectrum with the mobility ranging from 3 × 10-2 cm2/V·sec. to 3 × 10-4 cm2/V·sec. was observed during four hours. A small hump appeared in the spectrum of mobility ranging from 1 × 10-2 cm2/V·sec. to 1 × 10-1 cm2/V·sec. under the condition that the radioactive equilibrium state was held in the vessel. The concentration ratio in each fine range of mobility was distributed from 1 to 1.5.