Impulse approximation for cusp electron production from targetKandLshells

The forward peak resulting from electron capture to the continuum of bare projectiles is investigated within the impulse approximation in both its prior and post form. It is found that the asymmetry of the peak as well as the peak intensity increases if a larger number of interactions between the electron and the projectile is included in the calculation. For strongly asymmetric systems with light projectiles, a peaking approximation becomes valid which factorizes the capture cross section into the ionization cross section times the projectile Coulomb normalization. Thus capture from excited states is easily included, and the factorization allows for a fast evaluation not only of the electron spectra but also of the impact-parameter distribution and the alignment. The theory is also extended to capture into Rydberg states. The collision systems He²⁺+He, p+He, and p+Ne are investigated, and comparison is made with available experimental data.