Screening effects and total cross sections of single, double and triple ionization of neon by fast electrons

Abstract

The Bethe–Born theory is applied to estimate the effective charges experienced by the ejected electrons at single, double and triple ionization of neon by fast electrons. The expansion coefficients appearing in the asymptotic expressions for total cross sections σn+ ~ [an+ln(Ei/In+) + bn+]/Ei are determined by fitting to these expressions the experimental data for single and multiple ionization of neon. Coefficients an+ and bn+ are seen to decrease exponentially with increasing number of ejected electrons. Empirical formulae are found to describe this behaviour. Analytical expressions for coefficients an+ are derived within the Bethe–Born approximation for single, double and triple ionization of neon. The effective charges are determined by assuming that the derived analytical expressions for an+ can be reduced to the empirical formula. It is shown that, in order to obtain the reasonable values for the effective charges, coefficient bn+ should be taken into consideration. It is also revealed that the inclusion of interaction between the ejected electrons in the final state in calculation improves the results.