A double area detector system for simultaneous small and wide-angle X-ray scattering

A novel area detector has been designed for material science SR studies, capable of simultaneously collecting the diffraction data in two angular regimes. The detector for collecting wide-angle X-ray scattering (WAXS) data consists of four taper-coupled CCDs arranged as a 2 x 2 mosaic with a central aperture about 40 mm in diameter, so permitting the inclusion of a distant on-axis CCD detector for small-angle X-ray scattering (SAXS). The distance of the SAXS detector from the sample can be varied over the range 0.27 m to about 2 m, The overall aperture of WAXS detector is approximately 200 x 200 mm(2) allowing the measurement of the diffraction patterns from 5degrees to 45degrees with an average angular resolution of 0.05degrees. The parallax error for large angles is substantially reduced as the individual WAXS CCDs are tilted towards the specimen location. Both WAXS and SAXS diffraction data are simultaneously collected at 30 MB/s data rate, which is equivalent to 6 complete frames per second. Each pixel value is digitised using low- and high gain Analogue-to-Digital Converters (ADCs) which effectively increase the detector's overall dynamic range. The detector will be used in the study of a whole range of time-dependent phenomena, most importantly reaction kinetics, materials processing and real-time deformation studies. This paper discusses the unusual geometry of the system, how it relates to design optimisation and the techniques for recovering combined SAXS/WAXS patterns. (C) 2002 Elsevier Science B.V. All rights reserved.