scintillators

Scintillators are materials that emit light when they absorb ionizing radiation. This luminescence arises from excited states created in the material, which relax by emitting photons. Scintillators are used to detect and measure radiation by converting high-energy particles into a light signal, which can be read out by a photodetector.

Common inorganic scintillators include thallium-doped sodium iodide (NaI(Tl)), thallium-doped cesium iodide (CsI(Tl)), bismuth germanate (BGO), and lutetium-based crystals such as LSO and LYSO. Organic scintillators include plastic and liquid types, based on aromatic hydrocarbons with fluor dopants. Inorganic crystals generally provide higher density and higher effective atomic number, improving gamma-ray absorption, while organic scintillators often offer faster response and lower cost. Emission spectra are typically in the blue to green region, depending on material and dopant; activators such as thallium, cerium, and gadolinium play key roles in luminescence.

During irradiation, energy deposition creates electron-hole pairs and excitons that transfer energy to luminescent centers. Photons are emitted as these excited states decay. Light yield, decay time, and spectral output depend on the material. Light yields are commonly expressed as photons per unit energy (e.g., per MeV). Decay times range from sub-nanosecond in some organic scintillators to tens or hundreds of nanoseconds in many crystals; afterglow can occur in some materials.

Collected light is detected by photodetectors such as photomultiplier tubes, silicon photomultipliers, or avalanche photodiodes and converted into electrical signals for energy and timing measurements. Scintillators underpin medical imaging (PET and SPECT), gamma spectroscopy, high-energy physics calorimetry, and security screening.