A comprehensive theoretical treatment for the inelastic scattering of
fast electrons in a crystalline environment is applied to account for
variations in characteristic x-ray emission rates from spinel and chro
mia under zone-axis diffraction conditions for 300-keV electrons. X-ra
y counts as well as backscattered-electron contrast are recorded as th
e beam is tilted by about 70 mrad on a two-dimensional scan raster. Ca
lculated K-shell ionization and backscattering cross sections, based o
n a model which takes into account interaction delocalization, thermal
diffuse scattering, and the consequent thickness-dependent channeling
effects in a realistic way, are in good agreement with experiment.