Area detector design Part II. Application to a modular CCD-based detector for X-ray crystallography

Abstract

The performance of laboratory and synchrotron CCD-based detectors for X-ray crystallography is modeled using expressions which describe both the detector and the experiment. The detectors are constructed from an array of identical modules, each module consisting of a phosphor X-ray-to-light convertor, a fiberoptic taper and a CCD. The performance is characterized by the detective quantum efficiency (DQE) and dynamic range (DR), and by four additional expressions; the detective collective efficiency (DCE), experimental detective quantum efficiency (XDQE), experimental detective collection efficiency (XDCE) and experimental dynamic range (XDR). These additional expressions provide a means for including experimental constraints in the design of the detector. For a crystallography detector, these constraints include the requirements that the detector a) integrate Bragg peaks to maximum precision, and b) efficiently collect data to high resolution (large Bragg angle). Results obtained using these expressions demonstrate the need for a detector with a relatively large area. In order to build a such a detector from a reasonable number of modules using currently available fiberoptic tapers and CCDs, tapers with a demagnification ratio of > 3:1 are required. A different conclusion would be arrived at if the DQE alone were considered, demonstrating the importance of this method.