Editing Dynode

[[File:Dynodes.jpg|thumb|right|300 px|Two horizontal rows of arc-shaped dynodes in a photomultiplier tube.]]
A '''dynode''' is an [[electrode]] in a [[vacuum tube]] that serves as an [[electron multiplier]] through [[secondary emission]].  The first tube to incorporate a dynode was the [[Dynatron oscillator|dynatron]], an ancestor of the [[magnetron]], which used a single dynode.<ref name="Hull 1922">Albert W. Hull, E. F. Hennelly and F. R. Elder, The Dynatron Detector -- a new heterodyne receiver for continuous and modulated waves, [https://books.google.com/books?id=pwZEAAAAYAAJ&pg=PA320 Proceedings of the Institute of Radio Engineers] Vol. 10, No. 5 (Oct. 1922), pages 320-343</ref>  [[Photomultiplier]] and [[video camera tube]]s generally include a series of dynodes, each at a more positive [[electrical potential]] than its predecessor. [[Secondary emission]] occurs at the surface of each dynode. Such an arrangement is able to amplify the tiny current emitted by the [[photocathode]], typically by a factor of one million.<ref name="Hull 1922" />

==Operation==
The [[electron]]s emitted from the [[cathode]] are accelerated toward the first dynode, which is maintained 90 to 100 V positive concerning the cathode. Each accelerated [[photoelectron]] that strikes the dynode surface produces several electrons. These electrons are then accelerated toward the second dynode, held 90 to 100 V more positive than the first dynode. Each electron that strikes the surface of the second dynode produces several more electrons, which are then accelerated toward the third dynode, and so on. By the time this process has been repeated at each of the dynodes, 10<sup>5</sup> to 10<sup>7</sup> electrons have been produced for each incident photon, dependent on the number of dynodes. For conventional dynode materials, such as BeO and MgO, a multiplication factor of 10 can normally be achieved by each dynode stage.<ref>Glenn F Knoll - ''Radiation Detection and Measurement 3rd ed'', 1999, P270, {{ISBN|0-471-07338-5}}.</ref>

==Naming==
The dynode takes its name from the [[Dynatron oscillator|dynatron]]. [[Albert Hull]] did not use the term dynode in his 1918 paper on the dynatron,<ref>Albert W. Hull, The Dynatron -- A vacuum tube possessing negative electric resistance, [https://archive.org/stream/proceedings06inst#page/n13/mode/1up Proceedings of the Institute of Radio Engineers], Vol. 6, No. 1 (Feb. 1918); pages 5-35.</ref> but used the term extensively in his 1922 paper.<ref name="Hull 1922"/>  In the latter paper, he defined a dynode as a "plate that emits impact electrons ... when it is part of a dynatron."

==See also==
* [[Microchannel plate detector]]
* [[Photoelectric effect]]
* [[Particle detector]]
* [[Photodetector]]

==References==
<references />

[[Category:Electronic amplifiers]]
[[Category:Particle detectors]]