Parametric X rays observed under Bragg condition: Boost of intensity by a factor of two

Parametric x rays (PXR) produced by bombarding silicon and diamond crystals with electrons of 30 to 87 MeV were detected at 180 degrees relative to th e direction of the electron beam. It was found that the dependence of the i ntensity on the orientation of the crystal agrees with the predictions of t he kinematical theory of PXR. The absolute intensity is twice as large as p redicted. These findings can be explained considering dynamical effects tha t govern the x-ray crystal interaction. Additionally, x,rays caused by self -diffracted transition radiation have been observed.