Regional Basic Professional Training Course in Korea

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2. Radiation Protection
“semiconductor”. There are other mechanisms by which insulators can return excited
electrons back to the valance band. Since these crystalline materials are more dense than
gas, they have an increased ability to interact with radiation. In addition, they have much
better energy resolution characteristics.
2.4.2.1. Scintillation Detectors
One of the oldest techniques for detecting ionizing radiation makes use of the scintillation
light produced in certain organic and inorganic materials. Modern scintillation detectors
were developed primarily in response to the need for detecting higher counting rates and
consequently having shorter resolving times. In addition, this technique allows
measurement of the energy spectrum of beta particles and photons particularly at
relatively high energy values.
A number of different materials are employed as scintillators. These include single solid
organic crystals, organic materials dissolved in organic liquids or solids, plastics, thin
films, single crystals of inorganic material usually doped with some impurity atoms,
inorganic powders, glass, and high purity gases, usually noble gases, such as xenon and
krypton.
It is important that all scintillation materials have a high efficiency for conversion of
energy deposited by ionizing radiation to light (or very near ultraviolet) photons. This
process is called fluorescence and indicates the prompt emission of visible light photons
from a material following excitation of some sort. Phosphorescence, on the other hand,
signifies that emission of a longer wavelength photon takes place and that the
characteristic emission time is significantly delayed. Delayed fluorescence indicates that
the photon emission energy is the same as in prompt fluorescence, but that the emission
time following excitation is long. A good scintillator for radiation detection purposes
should convert a large fraction of the incident energy to prompt fluorescence with a time