Potentiometers for stabilizing a photomultiplier at high and strongly varying counting rates

The requirements placed on photomultiplier potentiometers are examined, with particular reference to two specific types: (1) a passive potentiometer with high cross-current, with a resistance chain separated at the last dynode, and (2) a potentiometer that regulates the dynode potential with the aid of cold cathode tubes that vary the mean multiplier current. In order to stabilize the amplification changes of a photomultiplier, it is necessary to build a low-ohmic potentiometer for the dynode potential. The procedures needed to build this ohmic potentiometer are presented in detail, stressing the circuit diagrams and their functions. It is determined after comparing the two potentiometers, that the use of the cold cathode tube potentiometer leads to a greater reduction in cross-current than by using the passive potentiometer.