ANALYSIS OF TRADE-OFFS BETWEEN SPATIAL-RESOLUTION AND DETECTIVE AREA IN CRYSTALLOGRAPHIC DETECTORS FOR USE WITH LARGE-UNIT-CELL CRYSTALS

Efficient acquisition of X-ray crystallographic data from crystals wit h one or more large unit-cell dimensions requires simultaneous resolut ion of many reflections that are tightly packed in reciprocal space. T his optimization requires careful matching of detector and beam charac teristics, including detector area and spatial resolution, beam intens ity and beam size. Two types of photon counting detectors have been de veloped at the University of Virginia for use with rotating-anode X-ra y sources. One is a flat gas-filled multiwire proportional chamber (MW PC) with delay line read-out and the other uses a solid X-ray absorber and contains microchannel plates (MCPs) with a delay line read-out. T he MCP detector has significantly better resolution than the MWPCs but has a smaller sensitive area. As an example of a methodology for comp aring the relative acquisition efficiencies of detectors used with rot ating-anode X-ray sources, the relative capabilities of these two dete ctors are calculated. The comparison is made over a range of unit-cell sizes, Bragg resolutions and crystal sizes, taking into account the i ntensities of the X-ray beams that optimize each detector's performanc e for a given set of crystal parameters.