X-ray data collection from mineral crystals by means of a position-sensitive detector: advantages and disadvantages

In order to check for the accuracy of X-ray diffracted data collected with an area-detector diffractometer (FAST-Nonius), we have carried out several data collections on a good-quality pyrope crystal (space group <Ia(3)over b ar d>, a = 11.479 Angstrom) under different: experimental settings and comp ared the results with those obtained with the same crystal mounted on a con ventional Philips PW1100 diffractometer. Several parameters have been teste d (detector gain, crystal-to-detector distance, frame width, integration ti me per image, beam intensity, shoebox size and re-measuring of overflow ref lections), and four critical features of the system have been identified: t he low thermal stability of the detector. its narrow dynamic range, the imp ortance of the detector-to-crystal distance and the integration of the diff racted intensities. We are now able to select the best experimental setting s in order to obtain a refinement from FAST diffraction data good as that f rom Philips data, in terms of R-sym, R-obs and standard deviation of the re fined parameters.