FOUR-CIRCLE DIFFRACTOMETER AND SMALL AREA POSITION SENSITIVE DETECTOR Meyer, M.; Paciorek, W. A., Chapuis, G. Universit de Lausanne, Institut de cristallographie, BSP, CH-1015 Lausanne (Switzerland), Phone: +(41) 21 692 37 81, Fax: +(41) 21 692 36 05, E-mail: Mathias.Meyer@ic.unil.ch

Single crystal X-ray reflections are intrinsically three-dimensional in nature. Conventional scanning (1-dimensional or [[omega]]-scanning) with a fairly large, finite aperture obscures the contributions of mosaic spread, spectral dispersion and source divergence by convolution of those entities. High-resolution 1-dimensional position sensitive detectors (PSD) allow an efficient implementation of the so-called [[omega]]/2[[theta]] slice scans as standard scanning technique. The fine 2[[theta]] resolution of the PSD along with the fine scanning in [[omega]] allows partly an experimental deconvolution of the aforementioned contributions. This idea was introduced by Mathieson (1982, Acta Cryst. A38, 378-387).

Based on these ideas we implemented a high resolution fibre-optically coupled 2-dimensional CCD-detector on a 4-circle Kappa-geometry diffractometer with an active area of 6.5 x 27mm². A 1-dimensional PSD can be simulated with the CCD detector by choosing an appropriate electronic and/or software binning ratio. An arbitrary subwindow of the active area may be defined. The detector resolution and data flow can thus be adapted to the particular problem of interest. The implementation allows thus an arbitrary combination of continuous, step or step-continuous scans with 0-, 1- or 2-dimensional detector windows. The short readout time for 1-dimensional images (60ms/image) allows the execution of [[omega]]/2[[theta]] slice scans as standard integration technique.

Experimental examples will include normal, incommensurate and twinned crystals and the sampling of diffuse scattering. The problem of extraction of integrated intensity from 2- and 3-dimensional slice scans will be addressed in this presentation.