An ionization chamber is an electrical device that detects various types of ionizing radiation. It consists of a gas-filled cavity surrounded by two electrodes of opposite polarity and an electrometer. As charged particles (radiation) pass through the gas, gas molecules ionize to produce ions and electrons. The electric field established between the electrodes accelerates the ions produced by the radiation to be collected by the electrodes. This charge is read by the electrometer and can be converted into an absorbed dose.
A proportional counter is a modified ionization chamber, one in which a higher voltage is applied, making the electric field near the axial cable strong enough to accelerate approaching electrons to such high energies that their collisions with gas molecules cause further ionization. The electric field allows the ionization chamber to operate continuously by cleaning electrons, which can cause ion pair recombination, resulting in a reduction of ion current.
A positively charged electret is used together with an ionization chamber made of electrically conductive plastic. This type of detector is ideal for use in uncontrolled environments, as its response has been proven to be consistent over wide temperature ranges (20 to 170 °C).
Ionization chambers are preferred for high radiation dose rates because they have no “dead time”, a phenomenon that affects the accuracy of the Geiger-Mueller tube at high dose rates. They also provide excellent energy resolution, which is mainly limited by electronic noise.
For data analysis, diffraction patterns are corrected for uneven detector response and normalized to the ionization chamber. Smoke detectors also have two ionization chambers, one open to the air and a reference chamber that does not allow particles to enter.
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