Dynode

A dynode is one of a series of electrodes within a photomultiplier tube. Each dynode is more positively charged 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 by typically one million. The electrons emitted from the cathode are accelerated toward the first dynode, which is maintained 90 to 100V positive with respect to the cathode. Each accelerated photoelectron that strikes the dynode surface produces several electrons, that are then accelerated to dynode 2, which is held 90 to 100V more positive than dynode 1. By the time this process has been repeated at each of the dynodes, 10⁵ to 10⁷ electrons have been produced for each incident photon. )