Differential partial ionization cross sections for 10-24 keV electrons colliding with helium and neon atoms

The relative differential partial ionization cross sections of helium and neon atoms for 10-24 keV electron impact have been measured by using an ejected electron-ion coincidence technique. Measurements were accomplished by employing a time-of-flight mass spectrometer for charge analysis of the ions and a channel electron multiplier working in a pulse-counting mode for detecting the slow electrons of non-discriminated energies ejected at 90degrees to the incident electron beam direction. The charge state fractions F-n of ions with charge states n are found to be nearly invariant with the impact energy. The present results show that the multiply charged ions of the target atoms are produced by different mechanisms, namely by a direct multiple ionization or by inner shell ionization followed by non-radiative transitions, for instance, by an Auger process combined with shake-off transitions. A good agreement is obtained between our experimental results and the calculations based on inner shell ionization cross sections folded with charge state abundances, which result from the decay of the corresponding initial inner shell vacancies.