Some Measurements of the Efficiency for Observing Photoelectrons in Image Intensifiers

A method is described for measuring the efficiency with which photoelectrons can be detected in an image intensifier system. A weak light is shone onto the first cathode and the photoelectron current measured. The light is then attenuated by a large known factor and compared with the number of spots observed in a given time. A simple system was used to demonstrate this method; a maximum efficiency of 85% was achieved. The results of experiments with a filament scintillation chamber and a Cerenkov detector using image intensifiers are discussed and yield some information about the electron detection efficiency. A simple method of finding the detection threshold is also mentioned with two typical examples of its results.