scintillation counter, device for detecting and measuring radiation by means of tiny visible flashes produced by the radiation when it strikes a sensitive substance known as a phosphor (see phosphorescence). Phosphors used in scintillation counters include zinc sulfide, sodium iodide, various liquids, and organic phosphors. The individual flashes are caused by absorption and reemission of radiation by the phosphor. They may be amplified by photomultiplier devices or amplified and converted to an electrical signal by photoemissive substances (see photoelectric effect). Scintillation counters may be used to detect the various types of radioactivity (alpha, beta, and gamma rays), cosmic rays, and various elementary particles.