Nine crystal multi-analyser stage for high resolution powder diffraction between 6 and 40keV

For powder diffraction, high resolution ran be best achieved using the parallel beam geometry with a monochromator/analyser combination. However experiments are long and a way to reduce this time without compromising ne resolution is to use several analyser/detector combinations mounted on a single theta(a)/2 theta(a) goniometer. We have developed such a solution for the "Powder Diffraction" BM16-ESRF beam line. This device comprises nine analyser/detectors, with a fixed prealigned offset of two degrees between adjacent analyser crystals, and can be used in the whole energy range of the powder diffraction instrument (from 6 to 40 keV). The only required adjustment is the classical theta(a)/2 theta(a) rotation of the supporting goniometer when the wavelength is changed. Moreover, the detector array can be used in the Debye Scherrer geometry without dismounting the multi-analyser stage, only by positioning the goniometer at an ad-hoc theta(a)/2 theta(a) angle, and inserting slits in front of the detectors. This multi-analyser system is mainly dedicated to high resolution experiments and a peak width (FWHM) of 0.006 degrees in 2 theta has been achieved with a Si(lll) monochromator on the BM16 ESRF beam line. Since the: prealigned offset is small (2(degrees)), the measuring time can be considerably reduced even fur scans of small angular ranges, for high energy experiments or for high resolution in-situ studies. This set-up has also been used for anomalous diffraction studies and experiments on amorphous coumpounds, where it provides efficient elimination of fluoresence scattering and background from ancillary equipment. This system is in operation on the ESRF powder diffraction BM16 beam line since 1996 and has been extensively used for more than 90% of the beam time.