2. Photomultiplier tubes

A photomultiplier tube is a detector which, on the one hand, converts the photons emitted by the radiation source into electrons, and on the other hand, amplifies these electrons to produce a current proportional to the number of incident photons. This technology dates back to 1936. A photomultiplier tube consists of a vacuum chamber (10 ^–4 · Pa) comprising (figure 1 ):

• an entrance window transparent to the radiation to be studied;

• a photoemissive cathode that photoelectrically...