Ionization chambers are electrical devices used to detect and measure the charge from the number of ion pairs created within a gas caused by incident radiation. They are preferred for high radiation dose rates due to their lack of “dead time”, a phenomenon that affects the accuracy of the Geiger-Mueller tube at high dose rates. The response of an ionization chamber depends on the voltage applied between the outer electrode and the center electrode, and they provide excellent energy resolution, mainly limited by electronic noise. High-pressure xenon ionization (HPXe) chambers are ideal for use in uncontrolled environments, as their response has been proven to be consistent over wide temperature ranges (20 to 170 °C).
Multi-cavity ionization chambers can measure the intensity of the radiation beam in several different regions, providing information on the symmetry and flatness of the beam. 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. Smoke detectors also use ionization chambers, one open to the air and a reference chamber that does not allow particles to enter. The detector voltage is adjusted so that the conditions correspond to the ionization region, and the voltage is insufficient to cause gas amplification (secondary ionization). Detectors in the ionization region operate at a low electric field strength, so gas multiplication does not occur.
The collected load (output signal) is independent of the applied voltage. Individual minimum ionization particles tend to be quite small and generally require special low-noise amplifiers for efficient operating performance. With reference to the attached ion pair collection graph, it can be seen that in the operating region of the ion chamber, the charge of a collected ion pair is effectively constant over an applied voltage range, since due to its relatively low electric field strength, the ion chamber has no multiplication effect. A proportional counter is one in which the voltage in the ionization chamber increases above a certain level. 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. Parallel plane, sometimes called a parallel plate, ionization chambers are commonly used in low energy (. Open-air ionization chambers are the defining instrument of the Roentgen unit and, as such, are fundamentally linked to the absorbed dose.
The alpha particle causes ionization inside the chamber, and the ejected electrons cause additional secondary ionizations. 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. With these power supplies, it is possible to adjust and maintain a constant voltage in order to obtain accurate readings.
