Ratios of total cross sections for electron-impact ionization and photoionization in Ar, Kr, and Xe in the energy range from 140 to 4000 eV for electrons and from 16 to 1012 eV for photons were measured. Comparatively low relative standard uncertainties of 1.3–1.9 % were achieved using an apparatus combining two recent instrumental developments. The first is associated with a highly accurate device for the determination of soft-x-ray and vacuum-UV photon flux, a cryogenic electrical substitution radiometer. The second is an upgraded ionization chamber for the precise comparison of total-ion yields for electron and photon impact. On the basis of our measured cross-section ratios and well-known total photoionization cross-section data, we deduced absolute total electron-impact ionization cross sections of the rare gases with relative standard uncertainties as low as 2%.

• Received 15 July 1999

DOI:https://doi.org/10.1103/PhysRevA.61.022723