Origin of photoionizing radiation in corona discharges in air

A hypothesis by Akishev et al (1999 J. Phys. D: Appl. Phys. 32 2399-409), that the photoionizing radiation emitted by the positive corona discharge in air is soft x-rays generated by electron bombardment of the anode surface, is discussed. Absorption curves of the photoionizing radiation generated by positive and negative coronae in atmospheric air are compared. The coincidence of the shapes of these curves confirms the earlier, widely accepted opinion that the photoionizing radiation is emitted by gas molecules and atoms, which are excited via electron collision. Photographic detection of this photoionizing radiation performed by the method proposed by Akishev et al is found to be improbable, because of the very high attenuation of radiation by the light protecting envelope around the photographic film.