Theory of coplanar asymmetric (e, 2e) reactions in helium

The triple differential cross section for the ionisation reaction e-+He(11S) to He+(1s)+2e- is analysed in the case of the coplanar, asymmetric geometry within the framework of the eikonal-Born series theory. Detailed calculations are performed for incident electron energies of 256 and 600 eV, and compared with recent absolute measurements. The authors find that second-order effects are crucial in explaining both the position and magnitude of the binary and recoil peaks.