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 with one or more large unit-cell dimensions requires simultaneous resolution of many reflections that are tightly packed in reciprocal space. This optimization requires careful matching of detector and beam characteristics, including detector area and spatial resolution, beam intensity and beam size. Two types of photon-counting detectors have been developed at the University of Virginia for use with rotating-anode X-ray sources. One is a flat gas-filled multiwire proportional chamber (MWPC) 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. The MCP detector has significantly better resolution than the MWPCs but has a smaller sensitive area. As an example of a methodology for comparing the relative acquisition efficiencies of detectors used with rotating-anode X-ray sources, the relative capabilities of these two detectors are calculated. The comparison is made over a range of unit-cell sizes, Bragg resolutions and crystal sizes, taking into account the intensities of the X-ray beams that optimize each detector's performance for a given set of crystal parameters.