4.3.2 Scintillators

Scintillation counters consist of a scintillator crystal and a photomultiplier. An incident gamma ray photon interacts with the material of the scintillation crystal and produce a spark of light (scintillation). These photons of visible light induce the ejection of electrons from the photocathode of the attached photomultiplier (photo-effect). The ejected electrons imping in successive dynodes of the photomultiplier and their quantity multiplies leading to a final electron cloud that strikes the anode. This induces a negative voltage pulse as output, with amplitude proportional to the energy of the incident photon. Scintillation counters are widely used in gamma ray spectrometry.