Radiation from polarized electrons in oriented crystals at high energy
  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. 
V. N. Baier and V. M. Katkov