A method and apparatus have been developed for precise measurements of the ratios of total cross sections for electron-impact ionization and photoionization in rare gases based on the comparison of the total ion yields of the two ionization processes. Low uncertainties for the cross-section ratios are achieved above all by using a cryogenic electrical substitution radiometer as a primary detector standard in the soft-x-ray and vacuum ultraviolet spectral ranges in order to determine the impinging photon flux. On the basis of our measured cross-section ratios and well-known total photoionization cross sections we deduce absolute total electron-impact ionization cross sections of rare gases. As a result we present ratios of total electron-impact ionization cross sections to total photoionization cross sections and deduce total electron-impact ionization cross sections of neon in the energy range of electrons from 140 to 4000 eV and of photons from 100 to 1500 eV. Relative uncertainties as low as 1.3% for the cross-section ratios and 2.8% for the total electron-impact ionization cross sections have been achieved. A comparison of our cross-section data with published experimental and theoretical data is presented.

• Received 10 April 1998

DOI:https://doi.org/10.1103/PhysRevA.58.2900