The significance of the lifetime and collection time of free electrons for the recombination correction in the ionometric dosimetry of pulsed radiation

The collection of free electrons in an ionization chamber results in a deficit of negative ions. The recombination of the ions in the chamber gas is therefore smaller than maintained by the classical recombination theory, which assumes an equal number of positive and negative ions. Under certain conditions the current induced by the electrons in the outer circuit of the chamber can be measured. If the lifetime and the drift velocity of the free electrons in the chamber gas are known, the collected electron-charge and therefore the deficit of negative ions can be found. The determination of the lifetime and the drift velocity is achieved by analysing the decay of the induced current following a short radiation pulse.