Semiempirical formulae for multiple ionization of neutral atoms and positive ions by electron impact

Semiempirical formulae for multiple-ionization (MI) cross sections sigma n of atoms and ions by electron impact are suggested for ejection three or more electrons n>or=3. The formulae have been deduced on the basis of available experimental data on sigma n and the assumption of the Born-Bethe dependence of sigma n on the incident electron energy E. The formulae suggested can be used for estimation of MI cross sections sigma n , n>or=3, from threshold up to high electron energies E approximately=10 5 eV for an arbitrary atomic or ionic target.