Figure 7.1 shows the output for a back-illuminated device with 1000 1keV photon events and 10 particle events, assuming the uniform illumination one would expect in subassembly calibrations. Note that most of the photon events are spread among several pixels at this energy. Most of the photon events are contained in a single pixel. This effect may have a power-law dependence with energy. The assumptions made in this X-ray CCD frame simulator limit its ability to reproduce actual CCD output.
Several enhancements are possible.
The complex geometry of the gate structure and the channel stops, and their similarly compicated electric field structure, should be included, especially for front-illuminated devices where photons must pass through these top layers of the detector in order to be recognized. Once an empirical estimate of these dependencies is available, it should be incorporated into the algorithm. In spite of its limitations, the current incarnation of the frame simulator is useful for addressing timely issues in CCD characterization. The program requires the user to supply a list of incident photons, providing each photon's energy and optionally its position, if the user wishes to simulate something besides uniform illumination.