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How does an ionization chamber detect radiation in a gas-filled container?

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detector output connected to a measuring circuit — radiation measurement Figure 1: (A) A simple equivalent circuit for the development of a voltage pulse at the output of a detector. R represents the resistance and C the capacitance of the circuit; V(t) is the time (t)-dependent voltage produced. (B) A representative current pulse due to the interaction of a single quantum in the detector. The total charge Q is obtained by integrating the area of the current, i(t), over the collection time, t_c. (C) The resulting voltage pulse that is developed across the circuit of (A) for the case of a long circuit time constant. The amplitude (V_max) of the pulse is equal to the charge Q divided by the capacitance C.

An ionization chamber detects radiation by utilizing a gas-filled container equipped with two electrodes maintained at a voltage difference to create an electric field.12

When incident radiation, such as a photon or charged particle, enters the chamber, it interacts with the gas molecules, transferring energy that results in ionization—the creation of ion pairs consisting of a positive ion and a free electron. Under the influence of the electric field, these charges are forced to migrate: the positive ions drift toward the cathode, while the electrons move toward the anode.132

This movement of charges constitutes an electric current that is measured in an external circuit. In the preferred ion-saturation region of operation, the measured current is directly proportional to the rate at which radiation creates charges within the gas. While typically used in current mode, these chambers can also function in integration mode by measuring the voltage drop caused by the collection of ionization charges over a specific period.2