Diffraction properties of deformed copper single crystals

This dissertation concerns the diffraction properties of deformed copper single crystals with emphasis on their behaviour as neutron monochromators. It presents an examination of the effect of crystal imperfection on the diffraction of gamma and neutron radiation, using transmission electron microscopy to determine the detailed defect structure. The basic diffraction equations for transmission geometry are studied as a function of wavelength and thickness for neutrons and γ-rays, and qualitative agreement between experimental and theoretical parameter is obtained. However the theoretical approach is dependent on an idealised defect structure, having a Gaussian distribution of lattice misorientations, which is rarely found in deformed copper single crystals. A relatively simple relationship between γ-ray and neutron rocking curves is only applicable to uniform defect distributions. The wavelength dependence of neutron absorption for the range 0.5 to 5.0Å is established theoretically for various neutron monochromator materials and experimentally for copper. The temperature dependence of this behaviour is also considered. The γ-ray diffraction is extremely sensitive to variations in the defect structure with position in the crystal, and this sensitivity is found to be dependent on both the dislocation density and the large-scale arrangement of dislocation structures. The dependence of the rocking curve width on the crystallographic direction of incidence could be reproduced qualitatively from a model in which bands of heavily deformed crystal are assumed to delineate regions of relatively perfect crystal. In order to determine defect densities and arrangements from γ-diffraction data x-ray theories were applied, but these also require a uniform microstructure, which was not found in the crystals examined. This is due to the neutron monochromator requirement of a large deformed single crystal. All crystals were deformed in compression, either as flat plates or as large rectangular blocks from which plates were cut.