DETECTORS AND DATA PROCESSING: OPTIMISED ANOMALOUS SCATTERING, HIGH RESOLUTION AND DYNAMICAL STUDIES. J R Helliwell, Chemistry Department, University of Manchester, M13 9PL, U.K.

The last 20 years has seen an important evolution of position sensitive detectors for crystallography data acquisition. Film densitometry, MWPC's, TV detectors, image plates and CCDs have been exploited. These devices all have strengths (true counting accuracy/sensitivity, MWPCs; wide wavelength response and high count rate, TVs/IPs/CCDs; large size, IPs) and weaknesses (wavelength range and count rate limits, MWPCs; detector noise, TVs; limited aperture, TVs/CCDs; poor duty cycle, IPs). In recent years very impressive results have been obtained with on-line IP devices, very large IP (Weissenberg) off-line devices, and on-line CCD devices. It has become possible, for e.g., in conjunction with cryoprotection against radiation damage of the protein sample, and/or intense, tunable synchrotron radiation, to readily measure multiple wavelength data sets, reach atomic resolution and record time-slicing dynamical protein crystallographic data. Examples include a brominated oligo-nucleotide MAD study on station 9.5 at Daresbury (IP), a seleno hydroxy methyl bilane synthase (HMBS) MAD study (collaboration with Dr A Haedener) at 9.5 (IP) and ESRF BL19 (CCD), a time-resolved study, also on HMBS, at ESRF BL3 and BL19 (CCD) and data collection on cryocooled concanavalin A to 0.94A (CCD compared with IP) at CHESS. In chemical crystallography examples include use of high photon energy (24 keV) and a CCD at CHESS with a nickel octahexylphthalocyanine and a temperature dependent space group transition. In neutron crystallography the use of IP's has started (e.g. neutron Laue of concanavalin A). Further evolution of detectors is important; the combination of the large aperture of IPs with the better duty cycle of CCDs might be possible with the 'pixel detector', a silicon based device with independent pixel counting chains. The ultimate diffraction measurement scheme of reflections measured only during their active range (seconds of arc rocking widths for lysozyme protein crystals have been realised using microgravity crystal growth) can yield optimal peak to background ratios. New sources beckon. Detector investment needs to be enhanced. Finally data processing at increased reflection measuring rates will be vital for full exploitation of both source and detector developments.