Particle Detectors
. Particle Detectors, instruments used to detect and study fundamental nuclear particles (see Atom ; Nuclear Energy ). These detectors range in complexity from the well-known portable Geiger counter to room-sized spark and bubble chambers. A. IONIZATION CHAMBER One of the first detectors to be used in nuclear physics was the ionization chamber, which consists essentially of a closed vessel containing a gas and equipped with two electrodes at different electrical potentials. The electrodes, depending on the type of instrument, may consist of parallel plates or coaxial cylinders, or the walls of the chamber may act as one electrode and a wire or rod inside the chamber act as the other. When ionizing particles of radiation enter the chamber they ionize the gas between the electrodes. The ions that are thus produced migrate to the electrodes of opposite sign (negatively charged ions move toward the positive electrode, and vice versa), creating a current that may be amplified and measured d