An electron multiplier or a continuous dynode electron multiplier, is a vacuum-tube structure that multiplies incident charges. The electron multiplier follows a process called secondary emission, in which a single electron can, produce emission of roughly 1 to 3 electrons when bombarded on metal or PbO coated surface. In this process, If an electric potential is smeared between the first metal plate and yet another, the emitted electrons will accelerate to the next metal plate and induce secondary emission of still more electrons. This process can very well repeated for a number of times. The result is a large shower of electrons all collected by a metal anode, all having been triggered by just one. This gets another name for electron multipliers that is avalanching ion detector. In a typical electron multiplier, 12 stages of acceleration will usually produce a gain in current of 10 million.
The electron multiplier can be triggered by any charged particle hitting the starting electrode with sufficient energy to cause secondary emission. Because of this reason the electron multiplier is often used as an ion detector. The electron multiplier can also be triggered by a photon causing vacuum photoemission of at least one electron. In case of a photomultiplier tube, a photo-emissive surface is followed by an electron multiplier with several sequential multiplying electrodes called dynodes. Because these electrodes are separate from each other, this might be called a "discrete-dynode" multiplier. A voltage divider chain of resistors is usually used to place each dynode at a potential 100-200v more positive than the previous one.
