There has been impressive progress in the theoretical treatment of electron collisions with atoms in the last decade. As a result, the fundamental collision problems of electron-hydrogen or electron-helium scattering are now understood fairly well. For heavier atoms, an accurate treatment of atomic ionization remains more elusive than atomic excitation due to the final-state three-body Coulomb problem. For higher impact energies, the first-order distorted-wave Born approximation is typically in reasonable agreement with fully differential cross sections ͑FDCS͒ for ionization. However, FDCS measurements are starting to be reported for lower incident electron energies and here agreement between experiment and theory is not good. In this paper we examine the importance of exchange distortion and the final-state electron-electron interaction on these collision processes.

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The triple-differential cross section for electron impact ionization of the 4s orbital of krypton (binding energy 27.5 eV) has been measured in coplanar symmetric kinematics. The experimental results are presented for outgoing electron energies of 85, 50, 20, 10 and 4 eV. The results are compared with two distorted wave Born approximation calculations; the influence of post-collision interaction (PCI) on the cross sections is investigated by incorporating correct final state boundary conditions in one of the calculations. The influence of PCI is found to be very important at the lower energies. Inclusion of the three-body final state boundary conditions improves the agreement between theory and experiment, but there are still significant discrepancies, indicating that additional physical effects (such as higher-order interactions) are important at lower energies.

The process of electron scattering from heavy target atoms is of considerable interest due to the enhanced role of relativistic effects and distortion of the electron trajectories resulting from the large value of nuclear charge. Here we present ͑e,2e͒ ionization measurements and distorted-wave Born approximation calculations for the scattering of spin-polarized electrons from xenon atoms in which the fine-structure levels of the residual ion are resolved. Comparison of measurements performed using a high-sensitivity toroidal analyzer spectrometer with the predictions of sophisticated calculations provide an improved understanding of the ionization dynamics of heavy target atoms and the treatment of electron exchange processes.

Even though spin-dependent effects are naturally associated with relativistic effects, it has been known for some time that significant spin asymmetries for electron-impact ionization are possible in a completely non-relativistic model if the J-state of the residual ion can be experimentally resolved. In the lowest order implementation of the same model, the spin asymmetry would vanish if the J-states of the ion are not experimentally resolved (i.e., summed over). Consequently, it is perhaps possible to search for relativistic effects by looking at asymmetries for which the final ion J-state is not resolved. There is also some experimental evidence that relativistic effects might be important for large scattering angles which are inaccessible to current experimental set-ups. If this is the case, relativistic effects might be seen in a double differential cross section measurement which integrates over all angles. Very recently, some significant experimental spin asymmetries for electron-xenon scattering have been reported for a doubly differential spin-asymmetry measurement in which the final J-state was not resolved. The purpose of this paper is to investigate whether or not these experimental results indicate relativistic effects.