SHORTENING OF DETECTOR SIGNALS WITH PASSIVE FILTERS FOR PILE UP REDUCTION: CALCULATIONS AND EXPERIMENTAL.

Abstract It is shown that the duration of detector signals does not set the ultimate limit to acceptable counting rates in linear systems. Unipolar signals shorter than the physical phenomenon taking place in the detector may be obtained by inserting a two-port, the transfer function of which approximates the inverse of the transfer function equivalent to the detector output. A system so compensated is termed “detector matched”. Iterative passive filters of bridged T type, most easy to construct, yielding a constant resistive impedance ( 50 Ω−50 Ω for instance ), may be inserted anywhere in the system. Results are shown for various devices: semiconductor detectors and scintillators, like plastics, anthracene and NaI(Tl). For fast scintillators the width of the signal may be reduced to nearly that of the photomultiplier SER. The effect on energy resolution is discussed.