Charging of particles in unipolar coronas irradiated by in-situ soft X-rays: enhancement of capture efficiency of ultrafine particles

The charging of fine particles in unipolar coronas irradiated by soft X-rays (3.5–9.5 keV,λ=0.13–0.41 nm) was studied. Voltage–current characteristics were used to examine the corona inception voltage in presence and absence of X-ray irradiation and to estimate the ion concentrations. The capture characteristics of synthesized particles: iron oxide, sodium chloride, silica and titanium dioxide, were established in coronas, with and without X-ray irradiation. Enhanced charging of ultrafine particles in coronas was observed in conjunction with soft X-ray irradiation. A positive corona with X-ray irradiation resulted in the highest charging efficiencies, followed by a negative corona with X-ray, X-ray only, negative corona only and finally positive corona only. Particle charging theories available in the literature were used to qualitatively explain the observed trends.