Intensity of Forbidden Neutron Reflections Simulated by Multiple Bragg Reflection

Abstract

Exploratory measurements have been made of the intensity of several forbidden neutron reflections simulated by multiple Bragg reflection in large single crystals. The (0003) and (0001) reflections were studied in a beryllium crystal with mosaic 0.25\ifmmode^\circ\else\textdegree\fi{} and the (200) in a germanium crystal with mosaic 0.02\ifmmode^\circ\else\textdegree\fi{}. Double-crystal methods were used with a triple-axis spectrometer. Large amounts of order contamination were treated by means of resonance absorption filters and least-squares analysis of overdetermined equations. To minimize the effect of peculiarities of individual specimens, the results are presented as intensity ratios. Simulated reflections were observed to have 1/60 to $\frac{1}{5}$ the intensity of ordinary Bragg reflections. No conclusive evidence was found for an intrinsic component due to the forbidden reflections themselves; the Be simulations were at least 200 to 700 times, and the Ge simulations at least 15 to 60 times, more intense than the corresponding intrinsic components. Caution must be used in applying these results to other specimens.