Scintillation

Scintillation is the emission of light by a material called a scintillator when it absorbs ionizing radiation or energetic particles. The emitted light is typically in the ultraviolet to visible range and can be detected to infer properties of the interacting radiation.

The process involves the rapid transfer of deposited energy into excited states of the scintillator, which de-excite by emitting photons. The light yield, measured as photons produced per unit energy absorbed, and the decay time of the light (often with fast and slow components) are key performance characteristics. Materials are chosen for high light yield, suitable emission wavelengths, fast response, and good energy resolution.

Common scintillators include inorganic crystals such as sodium iodide doped with thallium NaI(Tl), cesium iodide doped with thallium CsI(Tl), bismuth germanate (BGO), and lutetium oxyorthosilicate (LSO); organic scintillators such as plastic scintillators and liquid scintillators. The emission spectrum and decay characteristics depend on the material and its dopants or composition, influencing detector design and coupling to photodetectors.

In detection systems, the scintillator converts radiation energy into light, which is then collected by photodetectors such as photomultiplier tubes or avalanche photodiodes and transformed into electrical signals. These signals enable measurements of energy, timing, and sometimes particle type (with techniques like pulse-shape discrimination). Performance is affected by light yield, optical coupling, detector geometry, and temperature; afterglow can introduce background signals.

Applications span gamma-ray spectroscopy, positron emission tomography (PET), radiation safety and monitoring, high-energy physics experiments, and astrophysical or environmental detectors. In astronomy, a related use of the term refers to atmospheric scintillation—the rapid, random fluctuations in starlight caused by refractive index variations in Earth’s atmosphere.