Multiple scattering of axially channeled particles by thermal vibrations and electrons

Within the framework of the classical small-angle scattering theory a microscopic description of positively charged particle behaviour during axial channeling in a crystal is given. Assuming that statistical equilibrium in a transverse plane is established, the differential Fokker-Planck-type equation is obtained from the detailed-balance relation. The coefficients of this equation are determined by the atomic scattering potential and distribution function of scatterers and are studied at various relations between the amplitude of the thermal atom vibrations and their screening radius. It is shown that for relatively small depths (high transverse energies) the processes of direct particle knocking-out of a channel are predominant. At low transverse energies the scattering particle behaviour is determined by nuclear and electron diffusion processes. In this case, if the distance of closest approach of the particle to a chain exceeds considerably the amplitudes of atomic displacements, the corresponding coefficients are analogous to those obtained earlier. (author)