Pile-up effect for a counting channel with amplitude selection and imposed non-cumulative dead time

The performance of radioactivity counting systems is limited by pile-up which causes counting losses, timing uncertainties and incorrect energy selection. The counting signals are either single pulses for which amplitude distribution is observable at low count rate, or more complex signals for which the amplitude distribution is, for the superposition of rectangular pulses, the self convolution of the single-pulse spectrum. Without amplitude selection, the effect on the count rate is small. It is the same as an extending dead time equal to the width of a single pulse. However, amplitude selection reveals a more important distortion. The output count rate has been derived for a single channel analyser followed by a non-cumulative dead time. These results are confirmed by computer simulations. (orig.)