Model of the CCD indicating all different layers. X-rays entering from the top will be absorbed at a certain depth. An X-ray photon of low energy might be absorbed close to the field free region, losing part of its charge; higher energy X-rays will be absorbed closer to the gate structure and therefore the charge diffusion in the depleted region will be smaller (indicated by the flat mountain shaped area in the figure). At the right the potential in the CCD is indicated.