Quasi-Channelling: Nonfinite Periodic Motion of Particles along Atomic Planes in Crystals

Abstract

The motion of fast charged particle (electron or positron) through a single crystal along densely packed crystallographic planes can be adequately described as a motion in a periodic averaged smooth potential formed as a sum of potentials of parallel atomic planes. Here we consider the motion of particles with transverse energies ε ~ еU₀ close to the energy of potential barriers separating planar potential channels. Such motion is characterized by the possibility to move from one channel to another, as well as by the band quantum structure of allowed values of transverse energy. It is demonstrated that characteristics of motion, as well as parameters of accompanying electromagnetic radiation, are changing with a gap when a particle changes transverse energy from under-barrier level ε < еU₀ to over-barrier level ε > еU_0. Namely, the direction of particle drift in crystal deviates from the direction of channels and the frequency of its oscillations doubles. Simultaneously, the amplitude of deviations from the average drift direction decreases multiple times. As the result, the frequency of electromagnetic radiation emitted by the particle doubles and its intensity decreases abruptly. With further growth of transverse energy, the amplitude of oscillations decreases further, the frequencies of radiation emitted by the particle increase, but its intensity decreases.