Table of contents

The review treats the problem of radiation of relativistic charged particles in matter. The radiation of fast particles in an external field is considered from a unified point of view for an amorphous medium and for a single crystal. The basic attention is paid to the process of radiation in a single crystal where an enhancement of the radiation occurs as compared with an amorphous medium. This effect is shown to be due to the coherent and the interference mechanisms of radiation of relativistic particles in single crystals. First we outline the Born theory (quantum and classical) of coherent radiation of fast particles and show that this theory is valid if the particle propagates through the crystal far from the directions of channeling and if the scattering angle of the particle is small compared with the typical radiation angle of a relativistic particle. Then we show that a violation of these conditions leads to new effects in radiation such as, e.g., the effect of intense radiation of superbarrier and channeled particles, and the effect of suppression of coherent radiation. The comparison of theoretical and experimental results confirms the existence of new effects in the radiation. In conclusion, we review briefly new physical effects that must take place in single crystals at high energies in several other electrodynamical processes.

Several mechanisms for emission of electromagnetic radiation by relativistic electrons in various media which are of interest for generating intense ultraviolet, x-ray, and γ radiation are examined. Theoretical and experimental results on ultraviolet and x-ray Cherenkov radiation, quasi-Cherenkov radiation in artificial periodic structures, radiation from crystals which results from the diffraction of virtual photons, and radiation accompanying channeling are discussed.

The development of high-pressure technology has in recent years permitted obtaining extensive new information on the properties of hydrides of group VI–VIII transition metals. In this review, the experimental procedures for compressing macroscopic quantities of hydrogen to record high pressures, phase transitions, and structures of new high-pressure phases in Me–H systems are briefly described. Special attention is devoted to the magnetic properties of solid solutions of hydrogen in 3d metals and their alloys, whose study has yielded definite conclusions concerning the effect of hydrogen on the band structure and exchange interaction in these materials. The role of structural instabilities in the formation of superconducting properties of hydrogen solutions in 4d metal alloys based on palladium is examined.

The elementary effect of induced transition interaction of a moving charge crossing the boundary between two dielectric half-spaces with the field of a monochromatic wave scattered at this boundary is studied. The quantitative relation between this effect and the corresponding collective process of excitation of charge density waves at the same nonuniformity, i.e., the modulation of the flux of charged particles by the field of a counter-propagating wave, is found. The contribution of the physical phenomena under investigation to the development of beam instabilities and electromagnetic wave generation is discussed.