A voltage is applied between the electrodes. Negative charges are attracted by the anode, positive charges by the cathode. Operation as an ionization chamber involves the use of an applied voltage that is large enough to collect all ion pairs (positive ion and removed electron) produced in the gas by a radioactive source, but not large enough to cause any amplification of the gas. Small ventilated air ionization chambers with a volume of 0.01 to 0.3 cm3 are considered suitable for the measurement of field parameters up to 2 cm × 2 cm.
Multi-channel xenon ionization chambers pressurized up to 20 bar were developed in the 1970s and 1980s (Drost and Fenster, 1982, 198) and were successfully used on several clinical computed tomography (CT) scanners, such as the Philips 768-channel LX CT, the General Electric model CT 90000 Series II, and the Siemens Somatom CR model. Ionization chambers are widely used to assess the activity of artificial radionuclides during processing. The transmission ionization chamber generally consists of layers of PMMA coated with conductive material. An instrument that detects and measures ionizing radiation by measuring the electrical current that flows when radiation ionizes gas in a chamber, making the gas a conductor of electricity.
A more recent application of primitive total ionization chambers (such as the electroscopes used, for example, by Rutherford in the early 20th century), is based on the use of an electret, which maintains a charge for an extended period and is discharged by exposure to radiation. Ionization chambers with transparent X-ray plates made of aluminized plastic or thin metal mesh are used for the detection of fluorescent radiation. Proportional meters are more sensitive than ionization chambers and are suitable for measurements in low-intensity radiation fields. The ionization chamber is the only gas-filled detector that allows direct determination of the absorbed dose.
A positively charged electret is used together with an ionization chamber made of an electrically conductive plastic. After exposure to radiation for a period of time, the ionization produced in the chamber discharges the condenser; the exposure (or air kerma) is proportional to the discharge, which can be read directly against the light through a built-in eyepiece. When ionization chambers are not the most appropriate detectors for side profile measurements, an alternative is to use 2D detectors such as scintillation detectors14,15 and Gafchromic films. The electric field allows the ionization chamber to work continuously by cleaning electrons that can cause ion pair recombination, which can result in reduction of ion current.
An ionization chamber measures charge from the number of ion pairs created within a gas caused by incident radiation. Ionization chambers consist of a pair of charged electrodes that collect ions formed within their respective electric fields.