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

Abstract

For powder diffraction, high resolution can be best achieved using the parallel beam geometry with a monochromator/analyzer combination. However experiments are long and a way to reduce this time without compromising resolution is to use several analyzer/ detector combinations mounted on a single (theta) <SUB>a</SUB>/2(theta) <SUB>a</SUB> goniometer. We have developed such a solution for the 'Powder Diffraction' BM16-ESRF beam line. This device comprises nine analyzer/detectors, with a fixed prealigned offset of two degrees between adjacent analyzer 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) <SUB>a</SUB>/2(theta) <SUB>a</SUB> 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-analyzer stage, only by positioning the goniometer at an ad-hoc (theta) <SUB>a</SUB>/2(theta) <SUB>a</SUB> angle, and inserting slits in front of the detectors. This multi-analyzer 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(111) monochromator on the BM16 ESRF beam line. Since the prealigned offset is small (2 degrees), the measuring time can be considerably reduced even for 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 compounds, where it provides efficient elimination of fluorescence 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.