Coplanar symmetric (e,2e) cross section on helium and neon

Triple differential cross sections measured in a coplanar symmetric geometry on helium and neon at 100 eV and 500 eV incident energy are compared with a distorted-wave Born approximation of Zhang et al. (1989). The agreement is better for 500 eV than for 100 eV and better for helium than for neon. Additionally, measurements on helium at lower energies have been performed. The angular correlations strongly vary with the impact energy. At 500 eV, the peak around 45' which has its origin in binary collisions is largely dominating. With decreasing energy, its relative importance diminishes while the peak around 120' takes over. Both peaks are nearly equal at 50 eV and the distribution reduces to a single peak around 95' at 26.6 eV. There are no theoretical results for comparison at these energies.