Channeling of fast positrons on a crystal surface in a uniform magnetic field

The conditions of channeling of relativistic positively charged particles near the surface of a crystal in the presence of a magnetic field parallel to the surface are studied. It is shown that the emission spectrum of a single particle is discrete. The frequency of the first harmonic and the number of harmonics, making a significant contribution to the spectrum depend strongly on the initial coordinates and velocities of the particles. When averaged over the initial coordinate of the particle, the spectrum becomes continuous. The spectral range in which the radiation of parallel beam of particles is generated, does not depend on the magnetic field and is determined only by the energy of the particles and the averaged potential of the surface atomic layer. Radiation is concentrated in a narrow cone in the direction of the average velocity of the particles and polarized essentially in the plane orthogonal to the crystal surface.