THE PERFORMANCE OF THE AUSTRALIAN POWDER DIFFRACTOMETER AT THE PHOTON-FACTORY, JAPAN

Australian scientists have built and installed an X-ray powder diffrac tometer of an unusual design on the Australian beamline at the Photon Factory synchrotron-radiation facility within the National Laboratory for High Energy Physics (KEK), Tsukuba, Japan. The diffractometer is a Debye-Scherrer camera of 0.573 m radius. The place of the cylindrical film in a conventional camera of this type is taken by image plates. To minimize scattering and absorption by air, the instrument can be ev acuated. The instrument is now in operation and has been tested with a specimen of the rutile phase of TiO2. This material has been thorough ly studied previously and it has been demonstrated that time-of-flight neutron powder diffraction, conventional neutron powder diffraction, single-crystal neutron diffraction and single-crystal X-ray diffractio n lead to a consistent set of values for the anisotropic thermal param eters and the one positional parameter. The powder specimen of rutile for use at KEK was diluted with gum tragacanth and inserted into a gla ss capillary of 0.5 mm diameter. The beam from the synchrotron is inci dent on a silicon (111) channel-cut monochromator. Data were collected to +/-165 degrees 2 theta at wavelengths of 0.62, 1.10, 1.54 and 1.90 Angstrom. The exposure time for each data set was 10 min. The resolut ion of the instrument agrees with theoretical prediction and is such t hat the full width at half-maximum of a reflection varies from 0.04 de grees at 20 degrees 2 theta to 0.2 degrees at 160 degrees 2 theta for a wavelength of 1.54 Angstrom. The intensity from a 10 min exposure is more than sufficient for Rietveld refinement (R(exp) < 1%).