An ionization chamber is an instrument constructed to measure the number of ions within a medium. It usually consists of a gas filled enclosure between two conducting electrodes (the anode and cathode). When gas between the electrodes is ionized by any means, such as by gamma rays or other radioactive emission, the ions and dissociated electrons move to the electrodes of the opposite polarity, thus creating an ionization current which may be measured. Each ion essentially deposits or removes a small electric charge to or from an electrode, such that the accumulated charge is proportional to the number of like-charged ions. A voltage potential that can have a wide range from a few volts to many kilovolts can be applied between the electrodes; depending on the application. Ionization chambers are widely used in the nuclear industry as they provide an output that is proportional to radiation dose.
Ionization chambers are used in nuclear medicine to determine the exact activity of radioactive dose administered to the patients. Such devices are called 'radioisotope dose calibrators'.
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