Ionization Chambers
One of a pair of electrodes is a wire located centrally within a cylinder. The other electrode is the wall of the chamber. Radiation ionizes the gas within the chamber, permitting the passage of current between the electrodes. The thickness of a window in the chamber wall determines the type of radiation it can measure. Only gamma rays will pass through a heavy metal wall, glass windows will admit all gammas and most betas, and plastic (Mylar) windows are necessary to admit alpha particles. Counters of this type, when properly calibrated, will measure the total amount of radiation received by the body of the wearer.