  Radiation from high energy electrons in an oriented crystal can be considered
in a frame of the quasiclassical operator method which appears to be a most
satisfactory approach to the problem. Under some quite generic assumptions the
general expression is derived for the probability of circularly polarized
photon emission from the longitudinally polarized electron in oriented crystal.
The particular mechanism of radiation depends on interrelation between the
angle of incidence $\vartheta_0$ (angle between the momentum of initial
electron and axis (plane) of crystal) and angle $\vartheta_v \equiv V_0/m$
($V_0$ is the scale of a potential of axis or a plane relative to which the
angle $\vartheta_0$ is defined). When $\vartheta_0 \ll \vartheta_v$ one has
magnetic bremsstrahlung type of radiation (with corrections $\propto
\vartheta_0^2$ which are due to inhomogeneous character of field in crystal).
When $\vartheta_0 \gg \vartheta_v$ one obtains the theory of coherent
bremsstrahlung, while for $\vartheta_0 \geq \vartheta_v$ one arrives to the
modified theory of coherent bremsstrahlung. At high energy radiation in
oriented crystals is strongly enhanced comparing with standard bremsstrahlung.
