Performance model for high spatial resolution CsI scintillator screens coupled to CCD detectors

Abstract

A performance model for an x-ray imaging camera that is currently being developed at York University for the recording of crystallographic diffraction patterns produced by synchrotron radiation is presented. The camera is based on charge coupled device (CCD) sensors which are coupled to a CsI(Tl) x-ray scintillator screen using 3:1 reducing fiber optic tapers. The model predicts the accuracy to which diffraction spot intensities can be measured over a range of incident x-ray flux. The effect of the point spread function of the scintillator and optics and the typical expected diffraction spot geometry is included in the model and shown to have the most significant effect on the system performance for low spot intensities, limiting the camera's effective dynamic range. However, it is shown that quantum limited performance for incident dose fluxes as low as 100 photons per spot can be readily achieved in this design. Finally, the camera performance is predicted for x-ray energies above the scintillator K absorption edges (>33 keV). The effects of energy loss through scintillation K shell fluorescent escape photons reduces the camera's detective quantum efficiency.