An ionization chamber is a type of radiation detection device that is widely used for the detection and measurement of certain types of radiation. It consists of a gas-filled cavity surrounded by two electrodes of opposite polarity and an electrometer. When charged particles (radiation) pass through the gas, gas molecules ionize to produce ions and electrons. These ions and electrons are then accelerated by the electric field established between the electrodes and collected by the electrodes.
This charge is read by the electrometer and can be converted into absorbed dose. 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). This means that 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. Ionization chambers are preferred for high radiation dose rates because they have no “dead time”, a phenomenon that affects the accuracy of the Geiger-Mueller tube at high dose rates. This is because there is no inherent signal amplification in the operating medium; therefore, these meters do not require much time to recover from large currents. In addition, because there is no amplification, they provide excellent energy resolution, which is mainly limited by electronic noise. Parallel plane, sometimes called a parallel plate, ionization chambers are commonly used in low energy (<2 MeV). Small ventilated air ionization chambers with a volume of 0.01 to 0.3 cm3 are considered suitable for measuring field parameters up to 2 cm × 2 cm.
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. Ionization chambers are widely used in the nuclear industry, as they provide an output proportional to the radiation dose. They find wide use in situations where a constant high dose rate is measured, as they have a longer service life than standard Geiger-Müller tubes, which suffer from gas breakage below and are generally limited to a lifetime of around 1011 counting events. Therefore, ionization chambers can be used to detect gamma radiation and x-rays, collectively known as photons, and for this, the windowless tube is used. 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.). Ionization chambers have a uniform response to radiation over a wide range of energies and are the preferred means for measuring high levels of gamma radiation. Proportional meters are more sensitive than ionization chambers and are suitable for measurements in low-intensity radiation fields.
Radiation indicators are considered, whereas ionization chambers are used for more quantitative measurements. The transmission ionization chamber generally consists of layers of PMMA coated with conductive material. With 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. Absorption within an ionization chamber can be controlled by selection of make-up gas composition and pressure.
