Polarization approximation for electron cascade in insulators after high-energy excitation

The electron cascade after the absorption of a high-energy photon or collision of a high-energy particle is studied using the polarization approximation, which allows the peculiarities of the dielectric permittivity to be accounted for. The main effect of the frequency dependence of the dielectric function can be observed for secondary electrons with energies between the threshold of the inelastic scattering and a few plasmon energies. The expression for the threshold energy for Wannier-Mott exciton production is obtained in the parabolic band approximation. The competition of strongly inelastic scattering and phonon-assisted relaxation influences the total number of hot excitations produced by a fast particle. The role of dielectric properties is important for solids with a complicated electron energy structure, such as systems with d and f bands (e.g., rare earth compounds) and with high-lying outermost core bands (crystals with so-called crossluminescence, e.g. BaF2).