An ‘‘on’’-gated photomultiplier circuit for the determination of phosphorescence lifetimes

An ‘‘on’’-gated photomultiplier circuit is described which possesses a cutoff ratio >103 by switching dynodes 1 and 3 of a nine-stage side-on phototube (Hamamatsu models 1P28, R955, etc.). ‘‘On’’-gate delay and gate-width times are continuously variable between 150 ns and 10 ms. The ‘‘ringing’’ usually observed after the gate opening in similar circuit designs, due to the propagation delay in the dynode chain and the capacitive coupling between the anode and the switched dynodes, has been greatly reduced using a ‘‘spike compensator’’ circuit. When −1000 V was applied to the anode of the phototube, the resulting output of the circuit was linear 80 ns after the unit was triggered. The circuit will also operate as an ungated photomultiplier.