Electron exchange in the collisional ionization of atoms with outer s electrons

The Born-exchange and Ochkur approximations are used to calculate cross sections for the electron impact ionization of the atoms He, Li, Be, Na and Mg in their ground states. In all cases where there exists comparison data, the inclusion of exchange leads to better agreement with experiment as compared to ordinary Born cross-section calculations. Of the two exchange approximations considered here, the simpler approximation due to Ochkur consistently gives the best results.