Synopsis

Angular and energy distributions of electrons excited by a heavy charged particle penetrating an electron gas have been studied theoretically for a range of electron densities. The calculations are based on the self-consistent dielectric theory of Lindhard in which the properties of the electron gas are described by a frequency and wave-vector dependent dielectric function. The excitation cross section has been investigated in the present work for a broad range of incident projectile velocities, and numerical results are presented both for doubly and singly differential forms of the excitation spectrum. An analytical approximation is developed for the case of low projectile velocities, and comparison with numerical results indicates that the analytical form is quite adequate for velocities up to near the Fermi velocity. For higher incident velocities the emitted energy spectrum is char-acterized by a resonance for electron energies in the range — 1-4 times the Fermi energy; at electron energies about 10 times the Fermi energy the spectrum approaches that given by the Rutherford cross section. The electron energy at which the resonance occurs is independent of the projectile velocity, but is a slowly varying function of the electron density. The angular position of the reso-nance is, however, a strong function of the projectile velocity, occurring first in the forward direction at a critical velocity, u0, moving to higher angles with increasing projectile velocity, and limitin