Timing Slow Pulses for Fast Coincidence Measurements

The circuit described defines accurately the time of arrival of slow pulses. The circuit consists of a compensated delay univibrator generating a signal whose width increases with the input pulse height so that it ends at a time almost independent of the input trigger amplitude. The trailing edge of this signal shifts only 10 nsec when the input is varied from 0.5 to 10 V, and less than 5 nsec when it is varied between 1 and 9 V. The univibrator has been incorporated in a simple fast-slow coincidence circuit. Resolving times (2τ) of 10–30 nsec have been obtained with Co60 and NaI detectors without losing coincident events.