the ionizing effect of radiation on a gas is extensively used for the detection of radiation such as alpha, beta, gamma and x-rays. the original ionization event in these instruments results in the formation of an "ion pair"; a positive ion and a free electron, by ion impact by the radiation on the gas molecules. the ionization chamber is the simplest of these detectors, and collects all the charges created by "direct ionization" within the gas through the application of an electric field.