328 Chapter 6. Scintillation Detectors and Photodetectors
decrease in light output due to temperature increase is generally referred to as ther-
mal quenching. However only a few scintillators show a strong enough dependence
on temperature to be worried about.
D.4 EnergyQuenching
The light output of a scintillator depends on the energy delivered by the incident
radiation. However this process is not linear and eventually saturates at a certain
stopping power that depends on the material. Delivering more energy to the scintil-
lator beyond this point does not affect the light output. In such a state the material
is said to have suffered energy quenching. Since this effect is most pronounced in
organic scintillators, therefore it will be discussed in more detail later in the Chapter.
6.1.E DensityandAtomicWeight...................
Scintillation detectors are used to detect all types of radiation includingγ-rays,
electrons, neutrons,α-particles, and neutrinos. Efficient detection of these particles
depends on how well and how quickly they loose their energy in the scintillation
medium. These factors are characterized by the stopping power of the material,
which depends not only on the atomic weights of the constituents of the material
but also on their densities. for example detection of light particles such as photons
requires the material to have high effective atomic weight and high density.
Density and atomic weight are therefore important factors that are used to assess
the effectiveness of scintillation material for a particular kind of radiation and the
energy range of interest. There is no universal material that is good for all types of
radiation.
Although density and atomic weight are important parameters, but the reader
should note that they are not the only parameters that need to be considered. Other
factors such as opaqueness of the material to the scintillation photons may make an
otherwiseidealscintillation material worthless for use in a scintillation detector.
6.1.F Mechanical Properties and Stability
Vulnerability of scintillators to atmospheric conditions is well known. for example
due to moisture and temperature fluctuations the optical properties of some scintil-
lator deteriorate. Similarly changes in pressure may cause cracks. Hence mechanical
stability of solid scintillators is a major concern for detection systems.
Another important point is that the solid scintillators have to be cut, machined,
and polished after being produced. If they are not mechanically stable, they can not
be properly prepared for use in detectors. As we will see later, the plastic scintillators
have the kind of mechanical stability needed for mechanical manipulations.
6.1.G OpticalProperties
Most scintillators are developed such that they produce light in the visible region of
the electromagnetic spectrum. Since the photons thus produced have to be guided
to a photodetector to be detected therefore they must be able to travel through
the material without significant attenuation. Attenuation of photons causes loss