Scintillators and Photomultipliers

Spark chamber and its associated electronics

The scintillators are devices that produce light whenever a particle goes through it. This light is sent to a photomultiplier tube which converts this light to a flux of electron, an electric signal. The output of the photomultiplier is an analog signal w hich is converted to digital NIM by the discriminators. Both signals are fed in an AND gate which output a pulse whenever the signals are simultaneous. This signal goes to the spark gap driver amplifier and then to the spark gap itself.

Scintillator materials are made out of fluorescent plastic. Fluorescent materials have the special property to spontaneously emit energy, i.e. light, when their atoms are excited. This is exactly what happens when a charged particle hits the scintillators . They also have to be wrapped with black tape to avoid that external light interacts with the light emitted by the scintillators and hence sends false signals to the photomultipliers.

The photomultipliers use the photoelectric effect to produce electrons from photons. This small electric current is then amplified using a series of voltage drop and the output is an analog signal that can be used by other electronic devices. Light from the scintillator is brought to the photomultiplier (PMT) using light guides.