radiation detector that is triggered by a flash of light (or scintillation) produced when ionizing radiation traverses certain solid or liquid substances (phosphors), among which are thallium-activated sodium iodide, zinc sulfide, and organic compounds such as anthracene incorporated into solid plastics or liquid solvents. The light flashes are converted into electric pulses by a photoelectric alloy of cesium and antimony, amplified about a million times by a photomultiplier tube, and finally counted. Sensitive to X rays, gamma rays, and charged particles, scintillation counters permit high-speed counting of particles and measurement of the energy of incident radiation.