= Ionization chamber
An <ionization chamber> measures <ionizing radiation> by collecting the <electric charge> that it creates in a gas. Two <electrodes> establish an <electric field>; liberated <electrons> and positive <ions> move toward opposite <electrodes>. In the chamber's intended operating regime the field collects the initial charge with negligible <electron avalanche> multiplication, distinguishing it from a <proportional counter>.
Varying the applied <electric potential difference> while holding the incident <radiation> fixed produces a collection curve. Too weak a field allows <electron-ion recombination> before collection; an approximately flat region indicates near-complete collection under those conditions. Increasing the field far enough can instead cause gas multiplication. A 2013 <synchrotron radiation> experiment compared free-air chambers with different electrode gaps and chopped the X-ray beam, showing that collection depends on both geometry and the temporal delivery of <radiation>.<Current saturation in free-air ionization chambers with chopped synchrotron radiation by Nobuteru Nariyama>[abstract and sections 2–3: chamber gaps, chopped irradiation and recombination]{ref}
For a simple counting model, let each interacting <particle> create on average $n$ electron-ion pairs and let $f$ be their collected fraction. An interaction rate $r$ then gives mean <electric current> $I=efnr$, where $e$ is the <elementary charge>. This accounting explains why loss of charge can mimic a reduced incident <particle flux>; converting a current to <absorbed dose> requires additional information about <energy> deposition and the irradiated <mass>.
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