Cross section formulae for ionization and excitation of atoms by high energy electrons

Abstract

In the Bethe-Born approximation the cross sections for ionization or excitation of atoms by electrons of high energy E1, are given by σ=A/E1 ln cE1 for optically allowed transitions and by σ=B/E1 for disallowed transitions. Here A, B and c are constants for a given transition. For ionization or excitation processes to which both types of transitions contribute, the total cross sections are given by

These formulae are frequently simplified using the approximation cU ≈ c'U ≈ 4, where U is the ionization or excitation energy. It is shown that great deviations from these latter approximations occur.