1. A nuclear imaging apparatus comprising: an array of radiation sensors; and analog circuitry which performs a method comprising: receiving a current pulse; branching the current pulse into at least two pulses, to yield a first pulse and a second pulse; in a first path associated with the first pulse: delaying the first pulse; and shaping the first pulse, to yield a shaped current pulse; in a second path associated with the second pulse: subjecting the second pulse to a low-pass filter, to yield a filtered current pulse; differentiating the filtered current pulse, to yield a first derivative signal; and applying peak hold detection to the first derivative signal, to yield a slew-rate voltage selecting a percentage of the slew-rate voltage as a trigger level; and comparing the shaped current pulse to the trigger level.