What is an Ionization Chamber and How Does it Work?

An ionization chamber is 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. It is a type of radiation detection device that consists of two opposing electrodes placed in a gas-filled container and a high voltage is applied. As charged particles (radiation) pass through the gas, gas molecules ionize to produce ions and electrons. A well-type ionization chamber is composed of a cylinder containing the gas (nitrogen, argon, or gas mixture) under a given pressure and electrodes that will be used to collect electrical charges. Matsusada Precision offers a large number of high-voltage power supplies that can be used for ionization chambers with low ripple, compact body and 0 to 1 kV ratings.

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. Self-reading pocket dosimeters in the form of a pen, consisting of an ionization chamber that functions as a condenser, fully charged (corresponding to zero dose) before use. Gas ionization chambers measure charge from the number of ion pairs created within a gas caused by incident radiation. An ionization chamber and an electrometer require calibration before use and, with a triaxial connection cable, tools are required for calibration of the radiation beam. Proportional meters are more sensitive than ionization chambers and are suitable for measurements in low-intensity radiation fields.

Noble gas ionization chambers are simple, resistant to radiation, and are easily constructed in the 4π geometry used for accurate measurements of gamma-ray source activity (Suzuki et al.).This makes the output signal in the ionization chamber a direct current, unlike the Geiger-Muller tube which produces a pulse output. The transmission ionization chamber generally consists of layers of PMMA coated with conductive material. Regardless of their geometric design, ionization chambers used in diagnostic radiology must be of the ventilated type, that is, their volume of sensitive gas must communicate with the atmosphere. The ionization chamber is a radiation detector that is used to detect and measure charge from the number of ion pairs created within a gas caused by incident radiation. Therefore, a sufficient voltage of several tens to several hundred V is required in the ionization chamber.

Ionization chambers operate in region II and are an important type of radiation dosimeter as the primary device used for calibration of radiation therapy beams. Pressurized well type cylindrical ionization chambers are widely used for the determination of radioactive sample activity. Ionization chambers with transparent X-ray plates made of aluminized plastic or thin metal mesh are used for the detection of fluorescent radiation.

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