Ionization chamber
Ionization chamber
The Ionization chamber is the simplest of all gas-filled radiation detectors, and is used for the detection or measurement of ionizing radiation. Conventionally, the term "ionization chamber" is used exclusively to describe those detectors which collect ion pairs from gases
An ionization chamber is an instrument constructed to measure charge from the number of ions within a medium (which we will consider to be gaseous, but can also be solid or liquid). It usually consists of a gas filled enclosure between two conducting electrodes (the anode and cathode). The electrodes may be in the form of parallel plates (Parallel Plate Ionization Chambers: PPIC), or coaxial cylinders to form a convenient portable detector; in some cases one of the electrodes may be the wall of the vessel itself.
When gas between the electrodes is ionized by any means, such as by alpha particles, beta particles, X-rays, or otherradioactive emission, the ions and dissociated electrons move to the electrodes of the opposite polarity, thus creating an ionization current which may be measured by a galvanometer or electrometer. 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, depending on the application, can be applied between the electrodes. The applied voltage allows the device to work continuously by mopping up electrons and preventing the device from becoming saturated. The current that originates is called a bias current, and prevents the device from reaching a point where no more ions can be collected.
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