UNIPOLAR DIFFUSION CHARGING OF AEROSOL-PARTICLES AT LOW-PRESSURE

Experiments of unipolar diffusion charging of ultrafine aerosol particles (10-50 nm) at low pressure (0.2-0.5 atm) were performed. Aerosol charging was achieved using a novel unipolar charger which made use of a low-intensity alpha-ray radioactive source. The results of the experiments were compared with numerical solutions to the fundamental equations of charging. The Fuchs' limiting-sphere charging theory in the transition regime was used for the calculation of the combination coefficients between ions and particles. Good agreement was found between experimental results and numerical predictions of the charged fraction as a function of particle diameter.