Scintillation is a flash of light produced in a transparent material by an ionization event. The process of scintillation is one of luminescence whereby light of a characteristic spectrum is emitted following the absorption of radiation. The emitted radiation is usually less energetic than that absorbed. Scintillation is an inherent molecular property in conjugated and aromatic organic molecules and arises from the electronic structure of said molecules. Scintillation also occurs in many inorganic materials, including salts, gases, and liquids.
Scintillator is material which exhibits scintillation – the property of luminescence when excited by ionizing radiation. Luminescent materials, when struck by an incoming particle, absorb its energy and scintillate, i.e. reemit the absorbed energy in the form of light. Sometimes, the excited state is metastable, so the relaxation back out of the excited state is delayed. The process then corresponds to either one of two phenomena, depending on the type of transition and hence the wavelength of the emitted optical photon: delayed fluorescence or phosphorescence.
Scintillation Detector or Scintillation Counter
A scintillation detector or scintillation counter is obtained when a scintillator is coupled to an electronic light sensor such as a photomultiplier tube (PMT) or a photodiode. PMTs absorb the light emitted by the scintillator and reemit it in the form of electrons via the photoelectric effect. The subsequent multiplication of those electrons (sometimes called photo-electrons) results in an electrical pulse which can then be analyzed and yield meaningful information about the particle that originally struck the scintillator.
Applications for Scintillators
Scintillators are used by the government as Homeland Security radiation detectors. This application has a huge impact on Homeland security inspection. Scintillators can also be used in monitoring systems, neutron and high energy particle physics experiments, new energy resource exploration, X-ray security, nuclear cameras, computed tomography and gas exploration. CT scanners and gamma cameras in medical diagnostics are another way scintillators are used. A few more applications of scintillators are how they are used as screens in computer monitors and television sets. Nuclear material can be monitored using certain types of scintillators. Scintillators also generate light in fluorescent tubes.
Types of Scintillators
- Organic Crystal Scintillators – Organic crystal scintillators are aromatic hydrocarbon compounds which contain benzene ring structures interlinked in various ways. Their luminescence typically decays within a few nanoseconds.
- Organic Liquid Scintillators – Organic liquid scintillators are liquid solutions of one or more organic scintillators in an organic solvent. The typical solutes are fluors and wavelength shifter scintillators.
- Plastic Scintillators – The term plastic scintillator typically refers to a scintillating material in which the primary fluorescent emitter, called a fluor, is suspended in the base, a solid polymer matrix.
- Inorganic Crystal Scintillators – Inorganic crystal scintillators are usually crystals grown in high temperature furnaces, for example, alkali metal halides, often with a small amount of activator impurity.
- Gaseous Scintillators – Gaseous scintillators consist of nitrogen and the noble gases helium, argon, krypton, and xenon, with helium and xenon receiving the most attention. The scintillation process is due to the de-excitation of single atoms excited by the passage of an incoming particle.
- Glass Scintillators – Glass scintillators are sensitive to electrons and γ rays as well (pulse height discrimination can be used for particle identification). Being very robust, they are also well-suited to harsh environmental conditions.