A photocathode is a light sensitive device formed by a layer of a metallic substance such as cesium, sodium or antimony on a quartz or glass base and which discharges electrons when exposed to a certain level of luminosity. >
The electrons in the metal layer absorb the energy of the photons and send it to, for example, a photographic emulsion. This process is called photoemission. The number of electrons emitted by the photocathode is directly proportional to the amount of light that impinges on it. Therefore, the number of electrons is directly proportional to the amount of incident X-rays.
These devices are used in the construction of image intensifiers and television cameras.
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