Anomalous dispersion of slow neutrons in crystals

Studies of anomalous scattering of neutrons from CdI2 single crystals were continued over an energy range including the cadmium resonance peak at 0.178 eV. The complete (h 0 l) zone of reflections was measured at one wavelength (1.075 A) in order to permit a structure refinement which would simultaneously give a precise measurement of the complex scattering amplitude of cadmium at this wavelength. Selected reflections were also measured at several other wavelengths. In addition, a single crystal of 113CdI2 was grown, and Bragg intensities were measured for several reflections at 1.075 A. A complete least-squares refinement of the (h 0 l) zone was computed which included anisotropic thermal parameters as well as the complex scattering amplitude of cadmium. The latter is in remarkably good agreement with that calculated with the aid of the Breit-Wigner single level formulation using the neutron and gamma widths determined for cadmium by Brockhouse.