Gain stabilization of scintillation and Cerenkov spectrometers at high counting rates

A photomultiplier gain stabilization system, capable of operation at rates well over 5×10⁴ pulses/s, is described. Pile-up and dead-time effects, which hamper conventional systems at such rates, are minimized through the use of a fast-gated charge sensitive integrator directly coupled to the photomultiplier anode. Deviations in the time-averaged response to a reference light pulser are fed back to control the high-voltage supply. Rapid fluctuations due to variations in average dynode current are reduced through the use of active voltage divider chains. Stability, tested with a large NaI(Tl) crystal viewed by five photomultiplier tubes, is better than 0.7% over 24 h, and for counting rates charging from a few hundred counts/s to over 2×10⁵ counts/s.