Resonance errors and partial coherence in the inelastic scattering of fast electrons by crystal excitations

Due to boundary conditions imposed by the finite thickness of crystals used in electron diffraction experiments the change in wavevector of the fast electron need not precisely equal the wavevector of the crystal excitation involved in the scattering process. It is shown that this does not, however, lead to resonance effects. The degree of partial coherence between different processes is calculated for a perfect crystal.