THE AUSTRALIAN DIFFRACTOMETER AT THE PHOTON FACTORY

Outlined are design features of a versatile high-resolution two-axis diffractometer that is being constructed for operation at the Photon Factory as an Australian national facility. The instrument features optional use of multiple-imaging plates on a translating cassette to allow rapid recording of an almost complete range of data covering both the high-angle and small-angle scattering regime or alternatively the use of electronic detectors. The instrument will be capable of operation in various modes including the following: (i) high-resolution powder diffraction with single-channel counter and crystal analyzer, (ii) high-resolution, high-speed powder diffraction in the Debye-Scherrer mode with imaging plates as recording medium, either stationary or translating (for time-dependent studies), (iii) small-angle x-ray scattering with imaging plates as recording medium, (iv) protein crystallography in screenless Weissenberg mode, and (v) two- or three-axis single-crystal diffractometry. The salient features of the instrument are the use of a double-crystal sagittal focusing monochromator as primary monochromator together with the optional use of a condensing-collimating channel-cut (CCCC) monochromator or other channel-cut monochromator as secondary monochromator. The use of CCCC monochromator enables fine tuning of beam position on sample, harmonic suppression, beam-condensation, and variation of wavelength bandpass. Further features include the use of high-precision incremental encoders on both axes, together with the capability of operating the whole diffractometer, including secondary monochromator and detectors, in vacuum of order 10(-3) Torr in order to reduce absorption and parasitic scattering, and the use of a large camera radius (approximately 0.57 m) for the imaging plate cassette in order to increase angular resolution and signal to noise.