Differential partial ionization cross sections for 10–24 keV electrons colliding withhelium andneon atoms

Abstract

The relative differential partial ionization cross sections of helium and neon atomsfor 10–24 keV electron impact have been measured by using an ejectedelectron–ion coincidence technique. Measurements were accomplished byemploying a time-of-flight mass spectrometer for charge analysis of the ionsand a channel electron multiplier working in a pulse-counting mode fordetecting the slow electrons of non-discriminated energies ejected at 90°to the incident electron beam direction. The charge state fractionsFn of ions withcharge states nare found to be nearly invariant with the impact energy. The present resultsshow that the multiply charged ions of the target atoms are produced bydifferent mechanisms, namely by a direct multiple ionization or by inner shellionization followed by non-radiative transitions, for instance, by an Augerprocess combined with shake-off transitions. A good agreement is obtainedbetween our experimental results and the calculations based on inner shellionization cross sections folded with charge state abundances, which resultfrom the decay of the corresponding initial inner shell vacancies.