Multiple Bragg reflections of neutrons in an elastically deformed single crystal

The large positive diffraction intensity changes on forbidden (222) planes, which are produced by simultaneous diffraction, were observed when a perfect Si single crystal was excited into vibration. The excited Umweganregung effect is of the same order as the diffraction intensity obtained on (111) planes under the same experimental conditions. The theoretical consideration is an extension of the lamellae model usually used in the two-wave approximation. Both the theory and the experimental results demonstrate that such an effect may cause very large errors especially in diffraction experiments with non-perfect single crystals. (Auth.)