Where ionization chamber is used?

Ion chambers have a good, uniform response to radiation over a wide range of energies and are the preferred medium for measuring high levels of gamma radiation. They are widely used in the nuclear power industry, research laboratories, radiography, radiobiology and environmental monitoring. Pressurized well type cylindrical ionization chambers are widely used for the determination of radioactive sample activity. They are used as secondary measuring instruments, in particular for transferring standards and, thanks to their stability over time, periodically check the consistency of the measurement results of the primary activity over several years.

The fields of application of these instruments are varied, they are used in research, industry and nuclear medicine services. Their excellent stability over time, ease of implementation and excellent linearity according to activity levels are the main advantages of these standard radioactivity and transfer measurement instruments. 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. The unit is connected to an electrometer that will supply high voltage to the camera, acquire the current signal given by the camera and transmit it to the acquisition program.

A diagram of the configuration is shown below. A simple ionization chamber consists of a metal cylinder with a thin axial wire enclosed in a glass envelope in which some inert gas is filled with some inert gas. 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. The electric field allows the ionization chamber to work continuously by cleaning electrons that can cause ion pair recombination, which can result in reduced ion current.

Proportional meters are more sensitive than ionization chambers and are suitable for measurements in low-intensity radiation fields. A protective electrode is typically provided in the chamber to further reduce chamber leakage and ensure improved field uniformity in the active or sensitive volume of the chamber, with advantages in charge collection. Proportional counters work on successive ionization by collision between ions and gas molecules (charge multiplication); in the proportional region, amplification occurs (approximately 103-104 times) for the primary ions to obtain enough energy in the vicinity of the thin central electrode to cause more ionization in the detector. They act as solid-state ionization chambers when exposed to radiation and, like scintillation detectors, belong to the class of solid-state detectors.

This unique use of the CT chamber requires that the active volume response be uniform along its entire axial length, a restriction that is not required in other full immersion cylindrical chambers. 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. The ionization chamber is a radiation detector used to detect and measure charge from the number of ion pairs created within a gas caused by incident radiation. Multi-channel xenon ionization chambers pressurized to 20 bar were developed in the 1970s and 1980s (Drost and Fenster, 1982, 198) and were successfully used in several clinical computed tomography (CT) scanners, such as the Philips 768-channel LX CT, the General Electric Model CT 90000 Series II, and the Siemens Model Somatom CR.

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. When the gas between the electrodes is ionized by the incident ionizing radiation, positive ions and electrons are created under the influence of the electric field. .

Jada Urquiza
Jada Urquiza

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