Effect of X-ray energy and ionization time on the charging performance and nanoparticle formation of a soft X-ray photoionization charger

The present study is a detailed analysis of the charging performance of aerosol nanoparticles using soft X-ray photoionization. The study includes methods used to suppress the formation of unnecessary nanoparticles during ionization. Using a soft X-ray ionizer, the charging performance was evaluated at different emitting energies (3, 4 and 9.5 keV) and for ionization time and chamber type. The results were compared with the charging performance of an Am-241 α-ray ionizer. The experimental results showed that the total charging ratio for monodispersed nanoparticles is similar between X-ray and α-ray ionizers. However, a considerable amount of nanometer-sized particle formation caused by X-ray photoionization also was detected. Particle generation was significantly dependent on gas residence time in the ionization chamber, which was caused by ion-induced nucleation. Overall, the soft X-ray photoionizer is a more suitable bipolar diffusion charger because of a superior capacity for charging large numbers of dense aerosol particles in a relatively short residence time, which can be controlled in the ionization chamber.