An ionization chamber is a type of radiation detection device 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. This instrument is the most common method used to measure the absorbed dose in radiation beams from X-ray generators and cobalt 60 sources. Parallel plane, sometimes called a parallel plate, ionization chambers are commonly used in low energy (. In an ionization chamber, two opposing electrodes are 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. Two types of amplifiers are used to make the pulse height proportional to the amount of ionization produced by the particle in the chamber. A protective electrode is typically provided in the chamber to further reduce leakage from the chamber and ensure improved field uniformity in the active or sensitive volume of the chamber, with advantages in charge collection. 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.
An ionization chamber consists of a gas-filled cavity surrounded by two electrodes of opposite polarity and an electrometer. 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. They also act as solid-state ionization chambers by applying reverse polarization to detectors and by being exposed to radiation. 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.
Open-air ionization chambers are the defining instrument of the Roentgen unit and, as such, are fundamentally linked to the absorbed dose. In medical physics and radiation therapy, ionization chambers are used to ensure that the dose delivered from a therapy unit or radiopharmaceutical is as intended. Ionization chambers with transparent X-ray plates made of aluminized plastic or thin metal mesh are used for the detection of fluorescent radiation. Ionization chambers operate in region II (see Figure 6-26, B) and are an important type of radiation dosimeter as the primary device used for calibration of radiation therapy beams. The gas amplification curve describes the behavior of an ionization chamber as a function of the applied voltage.
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. A gas ionization chamber measures charge from the number of ion pairs created within a gas caused by incident radiation. This makes open-air ionization chambers the preferred reference dosimeter for Accredited Dosimetry Calibration Laboratories (ADCL), but their large size makes them unsuitable for clinical applications.
