Multiplier Phototubes for Single Electron Counting

Typical operating characteristics of ITT Industrial Laboratories' special purpose multiplier phototubes are described, with particular emphasis on the ability of these tubes to count single photoelectrons with minimum interference from dark noise. This ability, of particular significance in the detection of low energy quanta, including single photons, follows from the Poisson-like output pulse height distribution observed in the tubes in which a well-defined most probable pulse amplitude appears, compared to a more complex but lower amplitude dark noise pulse height spectrum. Other features of these tubes, such as adjustable cathode size and shape, electrical deflection for automatic gain calibration, alignment and image tracking, and reduction of dark noise with cooling, are also described.