A pulse shape discriminator for particle separation and pile-up suppression

Abstract

The double delay-line clipped pulses from a DD2 amplifier show a zero crossover point, which is constant within ≈2×10 −8 sec for a wide range of pulse amplitudes. Changes in the risetime of the input pulses due to different decay times of signals produced by particles with different ionization densities in a scintillation crystal result in a change of the zero crossover time. The same effect will take place due to pile-up of two pulses. The bipolar output pulses of the amplifier are analyzed in two channels: one for the positive going part of the pulses, another for the negative one. In both channels discriminators prevent triggering by suprious pulses. A variable delay of high resolution in the first channel brings the two output pulses to coincidence for a certain risetime of the detector pulses. A Garwin circuit detects the fast coincidence. The resolution of the coincidence is controlled by an output trigger stage, which delivers signals for the gate of a multi-channel analyzer. With (n,p) and (n,α) reactions produced by neutron bombardement of KI(Tl) and NaI(Tl) scintillation crystals, appreciable pulse shape discrimination was obtained. Pulse height spectra showing pulse shape discrimination and pile up suppression as well as the circuit schematics and its detailed description are given.