Coherent bremsstrahlung and channeling radiation from MeV electrons in silicon and gold

We report the observation of coherent bremsstrahlung in the range 1-25 keV from electrons incident at small angles to prominent crystal planes of thin silicon and gold crystals. We also find x radiation produced by electrons making transitions between bound quantized axial-channeling orbits in silicon and gold. We find no radiation above 1 keV from any bound planar-channeling states for either silicon or gold at electron energies up to 3.0 MeV.