GaAs as a backscattering crystal

The first neutron backscattering instrument was developed about 30 years ag o, and since this time, mainly silicon wafers were used as monochromator- a nd analyser-crystals. GaAs is another candidate for backscattering. The int ernal strains of GaAs wafers with a diameter of 10 cm were studied at five points of the diameter and reached a value Delta a/a approximate to 2.5 x 1 0(-5). These strains could be removed by cutting the wafer in pieces of 8 m m x 8 mm, giving a homogenous lattice constant within an experimental accur acy of Delta a/a = +/- 10(-6). The experimental value of the integrated ref lectivity of the (200)-reflex was determined to be R = 0.2 cm/s, which is i n excellent agreement with the width of the plateau of the Ewald reflection curve. The energy resolution of GaAs is expected to be ten times better th an that of silicon. (C) 2000 Elsevier Science B.V. All rights reserved.