A Review of the EMI Development of Photomultiplier Tubes

The structures of both production and developmental type photomultiplier tubes made by EMI are described and their characteristics presented. A departure from previous EMI tubes which has taken place in the past two years has been the development of a small box and grid structure system and recently a focused dynode system. The dark current characteristics of the EMI tubes are discussed particularly from the point of view of low energy counting. In the limit, a single beta particle of low energy in a scintillating phosphor may cause the emission of only 1 or 2, or 3 photoelectrons, and these are difficult to distinguish from the thermionic electrons emitted from the cathode. The problem is, therefore, to design and use photomultipliers so that as few thermionic electrons as possible are emitted from the cathode, and to reduce the collection of unwanted electrons from other parts of the cathode-Dl space. The results of development along these lines are presented.