3.5.2  Scintillator Detectors

The scintillators have the appearance of plastic. Toluene, anthracene, and sodium iodide, are some used substances to build them. The physicists build them in many forms. These depend on the particular practical necessities. For example: The beam detector is a square of $5~cm$ by $5~cm$; and hodoscope could be some square meters.

When a particle pass through a material excites its atoms and molecules; in a time of the order $1 \times 10^{-6}$ seconds the atoms decay emitting light -normally in the ultraviolet wave length-. The pass of the particles is registered by the luminous signal in the scintillator. The light is transmitted, through the same material, to a photomultiplier. There the signal is registered and amplified.

As the luminous signal is in the ultraviolet region and is weak, it is amplified before it is used. First a shifter of wave length is used to displace it to the visible region and after that a photomultiplier is used to amplify it.

Figure 5: Elementary particles; the structure of matter.

Figure 6: The structure of matter. Layers inside layers.

The most common used scintillators are organic monocrystals, plastics, and organic liquids. Also there are gaseous scintillators. The terrestrial atmosphere is as example.

The Figure 8 shows the typical array of a scintillator, the photomultiplier, and the electronics.

The spatial resolution of the scintillators, or array of scintillators, is very poor. They are used basically to detect the pass of particles. With them there are built systems to measure the time of flight of the particles. And knowing the distance of separation, measure the velocity of the particles. This is just the method of Galileo. With the modern electronics, the method works perfectly, even when the separation of the scintillators is of a few meters. The instruments are very precise. And they are completely automatized.