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•Esec. to 3 •~ 10-4 cm2/V•Esec. was observed during four hours. A small hump appeared in the spectrum of mobility ranging from 1 •~ 10-2 cm2/V•Esec. to 1 •~ 10-1 cm2/V•Esec. under the con dition 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.