Importance of second-order effects in large-angle, coplanar symmetric (e,2e) triple differential cross sections

The triple differential cross section for the ionisation of atomic hydrogen by fast electrons is analysed in the case of a coplanar symmetric, energy-sharing geometry. It is shown that at large scattering angles the second Born term of the scattering amplitude is more important than the first Born term, and that is governed by the contributions of the initial and final target states, acting as intermediate states. As a result of these second-order effects, the triple differential cross section exhibits a striking behaviour in the large-angle region.