Use of multiple Bragg reflections in a bent perfect single crystal for high resolution monochromatization of neutrons

Abstract

The effectiveness of the method of obtaining a highly monochromatic and collimated beam based on the well-known “Umweganregung” effect may be considerably improved when an elastically deformed single crystal is employed. In such a way a strongly excited multiple reflection effect produces a beam the intensity of which seems to be of practical use. For this purpose a very intensive umweg-effect simulating the 222 forbidden reflection of an elastically bent silicon single crystal at λ=0.156 nm was treated. The variable curvature of such a monochromator enables one to obtain a beam having a precisely fixed wavelength λ with a bandwidth Δλ λ in the range from 10 −4 to 10 −3 and collimation of the order of minutes of arc. Experimental and theoretical treatment has proved that in an elastically deformed crystal the double diffraction simulating a forbidden reflection (Umweganregung) can be assumed as a diffraction on a bicrystal system realized in one crystal.