scintillation counter A detector of high energy photons or particles. It employs the property of fluorescence produced in some materials when particles or photons traverse them. Large clear crystals of sodium iodide or potassium iodide are used in conjunction with a photomultiplier as gamma ray detector. For fast neutrons liquid phosphor containing boron compound is used. The magnitude of the output pulse from photomultiplier is proportional to the energy of the particles incident upon the phosphor. These pulses are amplified, and fed to a scalar circuit that counts the number of pulses. A pulse height analyzer can give the energy spectrum of the incident particles. As many as 10⁶ particles per second can be counted which is 200 times more than a GM counter*. Efficiency of gamma ray counting is much higher.