Annihilation of Relativistic Positrons in Single Crystal with production of One Photon

The energy and momentum conservation laws prohibit positron-electron annihilation in vacuum producing the single photon only. It can produce two photons in vacuum, or the process is possible with a participation of the third body. The situation is different in a single crystal with one of the leptons (e.g. positron) moving in the channeling (or in the quasi-channeling) mode when the transverse motion of a particle is bound or sufficiently uneven. It may increase sharply the probability of the single photon annihilation process.