Ion chambers are a type of radiation detector that measure the amount of ionization charge per unit mass of air. They are widely used in the nuclear power industry, research laboratories, radiography, radiobiology and environmental monitoring. An ion chamber is an extremely simple device that uses this principle to detect ionizing radiation. It consists of a conductive can, usually made of metal, with a wire electrode in the center, well insulated from the walls of the chamber.
The chamber is most commonly filled with ordinary dry air, but other gases such as carbon dioxide or pressurized air can give greater sensitivity. A DC voltage is applied between the outer can and the center electrode to create an electric field that sweeps ions toward the oppositely charged electrodes. Typically, the outer can has most of the potential relative to ground, so that the circuitry is close to the ground potential. The center wire is kept close to zero volts and the resulting current in the center wire is measured. One of the most important applications of ion chambers is the measurement of gamma ray exposure. They have a good uniform response to radiation over a wide range of energies and are the preferred means for measuring high levels of gamma radiation.
For example, if the inner surface of the ionization chamber is coated with a thin layer of boron, the (n, alpha) reaction can occur. At the junction between the reference and smoke chambers is the sensor electrode that is used to convert variations in chamber currents into a voltage. Ionization chambers can be used for neutron monitoring, either lined with a boron coating or filled with BF3 gas (see page 6). High-pressure xenon ionization (HPXe) chambers are ideal for use in uncontrolled environments, since the detector response is consistent over wide temperature ranges (20 to 170 °C). Sealed ionization chambers have a very small temperature coefficient, so cooling installations are only required if temperature variations greater than about 50°C are likely to occur. Most inspection instruments used to measure dose rate incorporate some type of device to allow beta-rays to enter the ionization chamber.
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. The power connector and control are removed and the holes suitable for the passage of the ionization chamber and the mounting holes are drilled. Ionization chambers with transparent X-ray plates made of aluminized plastic or thin metal mesh are used for the detection of fluorescent radiation. In conclusion, one of the most important applications of DC ion chambers is measuring gamma ray exposure. They have a good uniform response to radiation over a wide range of energies and are ideal for use in uncontrolled environments due to their consistent detector response over wide temperature ranges.
They also find wide use in situations where a constant high dose rate is measured due to their longer service life than standard Geiger-Müller tubes.
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