Most of the photon events are contained in a single pixel. Note how much more the particle events have bloomed - this is a result of the thick substrate assumed for this device. Radiation damage may also be included in the model, manifested by increased charge transfer inefficiency. 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 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. These traps have trapping times for electrons comparable to the row readout time. The key point is that the observed charge may no longer be strictly linear with incident X-ray energy, but may have a rate dependent effect.