Features of the Emission Spectrum during Channeling of Ultrarelativistic Leptons

The probability of photon emission by a channeled particle is calculated in the nondipole case. The emission of hard photons with energies comparable with the energy of the incident channeled particle is studied. The quasi-Bloch energy spectrum is calculated for an oriented fast charged particle entering a crystal at angles both smaller and larger than the Lindhard angle. The initial and final spectra of the channeled particle belong to different sets of the wavefunctions of the bands corresponding to different energies. The generation of photons by a quantum particle oriented with respect to the crystal and entering the crystal at angles both larger and smaller than the Lindhard angle are considered on the same basis. It is shown that the emission spectrum of hard photons consists of a set of distinct emission lines.