Modified reflection of X-rays

Abstract

As stated in an earlier communication, quantum theory leads to the remarkable conclusion that the reflection of X-rays in crystals is of two types; first, the classical or unmodified reflections associated with the normal structure amplitudes of the crystal; and secondly, the quantum or modified reflections which arise when the vibrations of the crystal lattice are quantum-mechanically excited by the incident X-radiation. The direction and intensity of the reflections of the second kind have been considered theoretically in a recent paper. It is shown that when the energy taken up by the crystal lattice is in the form of acoustic waves, the recoil of the photon is observable as a diffuse scattering of the incident X-radiation, while on the other hand, when the optical vibrations of the crystal lattice are excited, the resulting effect is a regular reflection of the incident radiation.