3 Scintillation Detectors for Charged Particles and Photons
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lattice, which shields the luminescent centres. However, the transport of light
through the crystal may be affected by the production of colour centres, which
absorb part of the scintillation light on its way to the photodetector. The formation
of colour centres results from the trapping of electric charges by crystal structural
defects or impurities and is therefore directly correlated to the quality of the raw
material and of the growth technology. A large effort is needed to purify the raw
materials to the required quality and to minimize the amount of structural defects
during the crystal growth. However, in some cases, a specific doping of the crystal
has proven to be an efficient and economical way of significantly increasing the
radiation hardness [8].
3.1.3 Scintillator Requirements for Various Applications
The choice of a scintillator depends on the energy of the ionizing radiation to be
detected and on constraints specific to the application. It is therefore tailored to the
user requirements considering the relative importance of several parameters, such
as density, light yield, scintillation kinetics, emission spectrum, radiation hardness.
Ruggedness, hygroscopic behaviour and production cost are also important parameters. In practice, it is impossible to find a scintillator, which combines all the most
desirable properties. Besides a number of industrial applications for process control,
container inspection, thickness gauging, ore processing and oil well logging a large
fraction of the scintillator market is driven by X-ray and γ-ray spectroscopy in the
following areas:
• High and medium energy physics particle detectors;
• Astrophysics and space applications;
• Spectrometry of low energy γ-quanta;
• Medical imaging;
• Safety Systems and Homeland Security.
The most important user requirements for each of these categories are detailed
below.
3.1.3.1 High and Medium Energy Physics Particle Detectors
Scintillators are used in High Energy Physics for compact, high precision, homogeneous electromagnetic calorimetry. The purpose is to measure with the highest
achievable precision the energy of electrons and photons, generally the decay
products of unstable heavier particles, over the widest possible energy range.
The first important requirement is a high density material. High energy implies
a high particle multiplicity of the particle collisions and requires a high granularity
with good lateral containment of the particle initiated showers in order to minimize
overlapping showers and to ease event reconstruction. A small Moliere radius is
53
lattice, which shields the luminescent centres. However, the transport of light
through the crystal may be affected by the production of colour centres, which
absorb part of the scintillation light on its way to the photodetector. The formation
of colour centres results from the trapping of electric charges by crystal structural
defects or impurities and is therefore directly correlated to the quality of the raw
material and of the growth technology. A large effort is needed to purify the raw
materials to the required quality and to minimize the amount of structural defects
during the crystal growth. However, in some cases, a specific doping of the crystal
has proven to be an efficient and economical way of significantly increasing the
radiation hardness [8].
3.1.3 Scintillator Requirements for Various Applications
The choice of a scintillator depends on the energy of the ionizing radiation to be
detected and on constraints specific to the application. It is therefore tailored to the
user requirements considering the relative importance of several parameters, such
as density, light yield, scintillation kinetics, emission spectrum, radiation hardness.
Ruggedness, hygroscopic behaviour and production cost are also important parameters. In practice, it is impossible to find a scintillator, which combines all the most
desirable properties. Besides a number of industrial applications for process control,
container inspection, thickness gauging, ore processing and oil well logging a large
fraction of the scintillator market is driven by X-ray and γ-ray spectroscopy in the
following areas:
• High and medium energy physics particle detectors;
• Astrophysics and space applications;
• Spectrometry of low energy γ-quanta;
• Medical imaging;
• Safety Systems and Homeland Security.
The most important user requirements for each of these categories are detailed
below.
3.1.3.1 High and Medium Energy Physics Particle Detectors
Scintillators are used in High Energy Physics for compact, high precision, homogeneous electromagnetic calorimetry. The purpose is to measure with the highest
achievable precision the energy of electrons and photons, generally the decay
products of unstable heavier particles, over the widest possible energy range.
The first important requirement is a high density material. High energy implies
a high particle multiplicity of the particle collisions and requires a high granularity
with good lateral containment of the particle initiated showers in order to minimize
overlapping showers and to ease event reconstruction. A small Moliere radius is