Conditions for generation of X-ray cherenkov radiation during motion of charges in realistic media

The influence of the spatial distribution of electrons, atoms, and nuclei in condensed media on a medium’s susceptibility and on the conditions for the formation of short-wavelength Cherenkov radiation are considered. It is shown that taking into account the inhomogeneous (atomic and electronic) structure of material media in which fast charged particles travel leads to a change in the effective susceptibility and permittivity in the X-ray range, as compared with cases of model homogeneous media with the same average concentration of electrons. The influence of the distribution functions of electrons and nuclei in a target on the conditions for Cherenkov radiation generation and its parameters and on the threshold energy of fast charged particles required to generate such radiation is studied. It is shown that the function of the spatial distribution of electrons and nuclei in a target affects the conditions for generating laser radiation in the X- and λ-ray ranges (on the problem of X- and λ-ray lasers). The obtained results show that using the Fresnel approximation in the X-ray range is insufficiently justified and can lead to significant errors.