  The radiation emission spectra of polarized photons emitted from charge
particle in single crystal are obtained in semiclassical theory in
Baer-Katkov-Strakhovenko approximation for planar crystal orientation. The
range of applicability of this approximation is estimated by comparing the
results with calculations in exact semiclassical theory. Optimal crystal
orientations for producing unpolarized and polarized photon beams are also
founded.
