Local Dead-Time Effects In Microchannel-Plate Imaging Detectors

Three different pinholes are imaged onto the microchannel-plate imaging detector to observe the dependence of the dead-time effects on the size of the area of illumination. The independent paralyzable-counter model is used to compare with experimental results. It is seen that the dead time increases rapidly as the area of illumination increases. This indicates that the coupling between channels in the microchannel plate is rather important. Therefore a model which assumes that the whole detector behaves as a single paralyzable counter is also examined. Both models give good agreement with the experimental mean, however they do not fit well with experimental values obtained for the variance of photocounts except for low count rates.