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Proceedings of the Institute of Radio Engineers ' VoWfik 24, Number 3 March, 1936
THE SECONDARY EMISSION MULTIPLIER—A NEW ELECTRONIC DEVICE*
V. K. Zworykin, G. A. Morton, and L. Malter
(RCA Manufacturing Company, RCA Victor Division, Camden, New Jersey)
Summary—This paper describes the construction, theory, and performance of various types of fixed field secondary emission multipliers. Detailed consideration is given of multiplier phototubes employing crossed electrostatic and magnetic fields and of electron multipliers using electrostatic focusing alone, to serve as coupling and amplifying units for cathode-ray tubes such as the "Iconoscope."
It is shown that while the power required for the operation of the secondary emission multiplier is about the same as that for the conventional amplifier, it is superior to the latter from the standpoint of noise. In the case of the multiplier phototubejihe signal-to-noise ratio is essentially determined by the shot noise of the phe'toemission, and is therefore sixty to one hundred times greater than that for a thermionic amplifier and phototube under conditions of low light intensity.
Multiplier phototubes have been built with an amplification factor of several millions and serve to replace the conventional phototube and accompanying amplifier system.
Their low "noise" level, together with their excellent frequency response and extreme simplicity, make these electron multipliers a very satisfactory form of amplifier.
FOR MORE than thirty years it has been known that when certain surfaces are bombarded with cathode rays they emit electrons. This effect, known as secondary emission, has, from an early date, been extensively studied by a large number of workers such as Lenard, Hull, Von Bayer, etc.
The study of this phenomenon revealed that the number of electrons emitted is proportional to the bombarding current, the factor of proportionality ranging from a mere fraction to ten times as many secondary as primary electrons. The value of this ratio depends upon the surface used and on the velocity of the bombarding electrons. . Although these facts have been known for a long time, the effect was not put to any useful work, except in the case of the dynatron invented by A. W. Hull. In fact, secondary emission had chiefly been looked upon as a serious obstacle in the design of thermionic vacuum
* Decimal classification: R535.38. Original manuscript received by the Institute, October 18, 1935; revised manuscript received by the Institute, November 21, 1935. Presented before New York meeting, October 23, 1935.