Light Yield

  The light yield (or light gain) is an important parameter of scintillation counters, in particular when signal detail is relevant like when scintillators are used for sampling hadron- or electromagnetic calorimeters. Only a small fraction of the energy loss of a charged particle in the scintillation counter is converted into visible light. This conversion factor is usually given relative to anthracene [Sangster56], whose light yield is of the order of 5% for blue light or about two photons/100 eV for high-energy particles. NaI has a light yield of about 230% of anthracene, while typical plastic scintillators give 50-60% [Bicron93].

For the effective light yield of scintillation counters, also the light collection, attenuation play an important role. When considering the number of photoelectrons on the photocathode of a photomultiplier in a typical electromagnetic calorimeter, the conversion efficiency on the photocathode must be taken into account. As the main fraction of energy loss occurs unobserved in the absorber sheets, one ends up with typically 1000 photoelectrons per GeV energy deposit in the calorimeter (see [Fabjan82].