Photon pile-up
= Photon pile-up
{title2=$\mu_{\rm event}\ll1$}
Two or more <photons> detected within one unresolved spatial and temporal event cell can be registered as one event, have their energies combined, or be rejected by event grading. In an X-ray <CCD>, low mean occupancy per event island per frame is needed for reliable individual-photon <spectroscopy>. Reducing frame time or spreading the image can reduce this effect.