Development and applications of the reverse neutron time-of-flight method with Fourier-type beam chopper: Dissertation

The neutron powder diffraction method has been applied to the crystal structure analysis of high temperature superconductors such as La1.8SrO.2Cu04-y, YBa2Cu307-y and Bi2Sr2CaCu208+y, optically active yttriumformate Y(HC00)3, and ß phase of deuterated acetonitrile, CD3CN. The structural information, containing symmetry, positional and thermal parameters, occupation factors and the order parameter, was obtained by measuring the coherent elastic scattering cross-section. The Rietveld profile refinement method was used for the extraction of structural parameters from experimental data. The diffraction spectra were obtained by measuring the time of flight distribution of neutrons with a Fourier type beam chopper. The neutron diffraction spectrum is created by the on line synthesis of the cross-correlation function between the beam modulation function and the detector intensity. Such an operational mode, called the reverse time- of flight method, has many unique properties. The possibility of filtering out a low frequency part of a diffraction spectrum, eg. incoherent background, by a properly selected band pass filter has been studied. One of the practical applications of the reverse time of flight method, the Mini Sfinks facility, is described with technical details, and its operational characteristics are compared with other high resolution instruments.