Polarization of bremsstrahlung at electron scattering in an anisotropic medium

Bremsstrahlung from relativistic electrons is considered under conditions when some transverse direction of momentum transfer is statistically preferred. It is shown that in the dipole approximation all the medium anisotropy effects can be accumulated into a special modulus-bound transverse vector, N. To exemplify a target with N²~1, we calculate radiation from an electron incident at a small angle on an atomic row in an oriented crystal. Radiation intensity and polarization dependencies on the emission angle and frequency for constant N are investigated. Net polarization for the angle-integral cross section is evaluated, which appears to be proportional to N²/2, and decreases with the increase of the photon energy fraction. A prominent feature of the radiation angular distribution is the existence of an angle at which the radiation may be completely polarized, in spite of the target complete or partial isotropy; that owes to existence of an origin-centered tangential circle for polarization in the fully differential radiation probability kernel. Possibilities for utilizing various properties of the polarized bremsstrahlung flux for preparation of polarized photon beams and for probing intrinsic anisotropy of the medium are analyzed.