What is an Ionization Chamber and How Does it Work?

An ionization chamber is a type of gas-filled radiation detector used to detect and measure certain types of ionizing radiation, such as x-rays, gamma rays, and beta particles. It consists of two electrodes arranged on opposite sides of a gas-filled volume. When a voltage difference is applied between the two electrodes, an electric field is created inside the gas. This electric field causes the ion pairs formed by the incident radiation to move towards the cathode and anode, respectively.

This movement of charges creates an electrical current that can be measured in an external circuit. There are several types of gas-filled chambers, each with its own mode of operation. Ionization chambers are filled with a noble gas or liquid in which the ionizing particle creates ion-electron pairs. The ions and electrons then travel under the applied electric field to the cathode and anode, respectively, where they are collected. If the electric field is increased, the electrons have enough energy to ionize the gas on their own and a gas multiplication region is reached.

Detectors using this mode of operation are called proportional counters. If the electric field increases further, for example, in a Geiger-Mueller meter, the electrons are so energetic that UV photons are emitted when they reach the anode. At the lower end of the voltage scale for gas-filled detectors are ionization chambers or ion chambers. By the end of the exposure period, the voltage in the chamber will have dropped since the ionization charge that is collected serves to partially discharge the stored charge CV0. This can also be achieved chemically with a cooling gas, such as halogen, that absorbs the additional photons created by an ionization avalanche without ionizing itself. To demonstrate its usefulness, liquid argon contamination can be studied using an α cell.

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