Elastic first Born matrix elements and systems containing large numbers of electrons

It is argued that the more electrons a target atom or molecule has, the higher one has to go in energy before the first Born approximation (FBA) to elastic electron scattering can be relied upon. For excitation processes, on the other hand, the FBA should be useful in roughly the same kind of energy range for a system containing a large number of electrons as for a system containing a small number of electrons, provided that the excitation processes considered are similar. Ramifications of these two results in the theory of heavy particle collisions are pointed out. Electron loss by hydrogen atoms passing through Ar is taken as an example. It is shown how the presently existing discrepancy between the Dmitriev and Nikolaev (1963) free scattering approximation to this process and the available experimental data can be corrected. Large differences between FBA calculations of heavy particle collision processes involving targets containing large numbers of electrons and experimental data are also explained and a solution proposed.