A dynode is one of a series of electrodes within a photomultiplier

Photomultiplier

Photomultiplier tubes , members of the class of vacuum tubes, and more specifically phototubes, are extremely sensitive detectors of light in the ultraviolet, visible, and near-infrared ranges of the electromagnetic spectrum...

 tube. Each dynode is at a more positive electrical potential than its predecessor. Secondary emission

Secondary emission

Secondary emission in physics is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some material, induce the emission of secondary particles. The primary particles are often charged particles like electrons or ions. If the secondary...

 occurs at the surface of each dynode. Such an arrangement is able to amplify the tiny current emitted by the photocathode

Photocathode

A photocathode is a negatively charged electrode in a light detection device such as a photomultiplier or phototube that is coated with a photosensitive compound...

, typically by a factor of one million.

Operation

The electron

Electron

The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

s emitted from the cathode

Cathode

A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

 are accelerated toward the first dynode, which is maintained 90 to 100 V positive with respect to the cathode. Each accelerated photoelectron that strikes the dynode surface produces several electrons, that are then accelerated to the second dynode, which is held 90 to 100V more positive than dynode 1. For conventional dynode materials, such as BeO and MgO, a multiplication factor of 10 can normally be achieved by each dynode stage. By the time this process has been repeated at each of the dynodes, 10⁵ to 10⁷ electrons have been produced for each incident photon, dependent on the number of dynodes.

Naming

The dynode is so named because it acts as a middle point between the (photo)cathode

Cathode

A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...

 and the anode

Anode

An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....

.

See also

• Microchannel plate detector
  Microchannel plate detector
  A micro-channel plate is a planar component used for detection of particles and impinging radiation . It is closely related to an electron multiplier, as both intensify single particles or photons by the multiplication of electrons via secondary emission...
  
  
• Photoelectric effect
  Photoelectric effect
  In the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as photoelectrons...
  
  
• Particle detector
  Particle detector
  In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify high-energy particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a...
  
  
• Photodetector
  Photodetector
  Photosensors or photodetectors are sensors of light or other electromagnetic energy. There are several varieties:*Active pixel sensors are image sensors consisting of an integrated circuit that contains an array of pixel sensors, each pixel containing a both a light sensor and an active amplifier...