Scintillation Counters

Scintillation counters are used to detect gamma, X-ray and neutron radiation. They consist of a detector for sensing incident radiation and a photomultiplier for producing countable pulses. Gamma radiation detectors are used to detect high-energy, short wavelength electromagnetic radiation of nuclear origin. X-ray radiation detectors detect X-rays, electromagnetic radiation that is similar to light but much higher in energy and frequency. Neutron radiation detectors are used to detect free neutrons that are emitted during nuclear fission, nuclear fusion, or other reactions in which a nucleus absorbs and alpha particle and emits a neutron. All three types of scintillation counters are used in a variety of applications, from medical imaging applications to dark matter detectors. They are also used aboard spacecraft to observe and measure sources of cosmic background radiation.

Scintillation counters consist of various components, the most important of which is the scintillator crystal. As a rule, these scintillator crystals emit low-energy photons when they are struck by the high-energy particles of a gamma-ray. The low-energy photons are collected by the photomultiplier tubes (PMTs) of the luminescence counter to determine the energy of the gamma ray radiation. The scintillator crystal used in a scintillation detector may be made from a variety of materials, depending upon the application. For use in a gamma-ray detector, the crystals are typically made of inorganic materials such as sodium iodide or cesium iodide with the addition of an activator or impurity such as thallium. Note that electroluminescence detectors are also used to detect gamma rays, and typically use pressurized xenon to detect the scintillation signals. Other types of scintillation counters are also available.

Scintillation dcounters include liquid detectors, devices which count flashes of luminescence that result from the interaction of the radiation with a liquid. Liquid-based scintillation counters involve a liquid medium rather than a scintillator crystal. A liquid detector is useful for detecting low energy emissions. Liquid detectors typically use two luminescence detectors that are positioned in opposition to each other. Each luminescence detector has a view of the flask or vial containing the liquid scintillator. When the liquid scintillator emits radiation, both luminescence detectors must detect the light for the count to be tallied. Liquid detectors and other scintillation counters may also be used for medical imaging applications such as positron emission tomography.

• Application Note: Liquid Scintillation (.pdf)
  Liquid scintillation provides a method for analyzing the concentration of radioactivity in an unknown sample. Detection is achieved by converting the kinetic energy of a nuclear emission into light...
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• Scintillation Detectors
  Scintillation dectectors use a solid or liquid material whose atoms are easily excited by the incoming radiation. These excited atoms emit visible light when they return to their ground state. Common...
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• Position Sensitive Detector (PSD)
  Position sensitive detectors (PSD) are proportional counters that use gas ionization and a localized electron-avalance process to amplify the signal from a detected X-ray. Both linear (1-D) and area...
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