Ionization cross section ratios of rare-gas atoms (Ne, Ar, Kr and Xe) by electron impact from threshold to 1 keV

Electron impact multiple ionization relative cross sections of rare gas atoms (Ne, Ar, Kr and Xe) have been measured using a pulsed electron beam and a pulsed ion extraction combined with a time-of-flight analysis of the charge. The measurements cover a larger range of energies and charges than in earlier experiments, from threshold to 1 keV and from charge n = 1 to 4 (Ne), 5 (Ar), 7 (Kr) and 6 (Xe). The average number (γ) of electrons ejected from the atom per ionization event is calculated and used to evaluate the contributions of the inner-shell processes. The results are also compared with those in the case of photon impact. As regards the major ions produced, relative uncertainty as low as 1.3% for the ionization cross section ratios is achieved for all the sample gases, except near threshold. As for the γ-values, relative uncertainty is estimated to be as low as 1.2%.