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What happens to gas molecules when radiation enters an ionization chamber?

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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.

When radiation, such as a charged particle or a photon, enters an ionization chamber, it interacts with the gas molecules contained within the device. This interaction converts neutral gas molecules into ion pairs, which consist of positive ions and electrons.12

Specifically, the radiation transfers energy to the gas molecules, causing the ejection of an electron from a molecule, which leaves behind a positive ion. In some cases, these detached electrons may also attach themselves to other neutral gas molecules to form negative ions.234

Once these charged particles are created, the electric field maintained within the chamber by the electrodes exerts a force on them. This causes the positive ions to drift toward the cathode and the electrons to migrate toward the anode. The movement of these charges constitutes an electric current that can be measured in an external circuit, providing a way to determine the intensity of the radiation.12