scintillations

Scintillation refers to the emission of light by a material after it absorbs ionizing radiation or is excited by high-energy processes. The term covers phenomena in both astronomy and radiation detection, though the underlying physics and applications differ.

In astronomy, scintillation describes rapid fluctuations in the apparent brightness of a distant light source caused by moving or varying refractive indices in a medium such as Earth's atmosphere or interstellar plasma. Atmospheric scintillation, often called twinkling, results from turbulence that alters the focusing of starlight as it travels through the atmosphere. The effect depends on wavelength, telescope aperture, observing altitude, and wind, and it can limit precision photometry. Adaptive optics and larger apertures are among common mitigation methods.

In radiation detection and nuclear instrumentation, a scintillator is a material that absorbs ionizing radiation and re-emits part of its energy as visible or near-visible light. The emitted light is detected by photomultiplier tubes or solid-state photodetectors, converting the light into an electrical signal. Scintillators are evaluated by light yield (photons per unit energy), emission spectrum, decay time, density, effective atomic number, and afterglow. Widely used inorganic scintillators include NaI(Tl), CsI(Tl), CaWO4, BGO, and newer crystals such as LSO. Applications span medical imaging (PET and gamma cameras), radiation spectroscopy, homeland security, and high-energy physics experiments.

Mechanistically, scintillation light arises when excitation relaxes through luminescent centers, often with multiple decay components from nanoseconds to microseconds. This distinguishes scintillation from longer-lived phosphorescence and from other luminescent processes not driven by ionizing radiation. Temperature, impurities, and material quality influence light yield and decay behavior.