True Zero-Crossing Fast Discriminator

This paper describes a discriminator for use with nuclear detectors that incorporates both a pulse height threshold and a true zero-crossing time detector. A negative doubly-differentiated signal is applied both to the base of an avalanche transistor and to a tunnel diode pulse height selector. The transistor is normally biased off but if the leading edge of the signal trips the tunnel diode, a pedestal is applied to the emitter of the transistor allowing it to avalanche when the input signal crosses zero. By driving the discriminator directly from the anode of a proton recoil scintillation detector, a total time shift of less than one nanosecond can be obtained for pulses ranging from 1.1 to 30 times threshold.