Production of electrons with energy greater than 50 keV by heavy ion-atom collisions

Cross sections were measured for the production of electrons with kinetic energies from 50 to 150 keV by heavy ion-atom collisions. The beams of 40 and 70 MeV nickel and 70 and 120 MeV bromine ions were produced by a tandem Van de Graaff accelerator and were incident on targets of carbon, nickel, potassium bromide, silver and gold. The energy spectra were measured using a steering electron spectrometer capable of 7% transmission and 4 keV resolution. The observed cross sections were compared with the predictions of the plane wave Born approximation with particular attention to the variation of cross section with respect to the electron energy. In the electron energy region observed the cross sections exceed the Born predictions by factors of 2 to 10 with deviation becoming more pronounced at high electron energy. The variation of the cross section with the incident beam energy is consistent with the Born prediction of a 4th power law dependence. The deviation of the cross section from Born approximation indicates that it may be necessary to invoke quasimolecular effects to fully interpret the data