THE SIGNIFICANCE OF THE LIFETIME AND COLL ECTION 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 chambe r gas is therefore smaller than maintained by the classical recombinat ion theory, which assumes an equal number of positive and negative ion s. Under certain conditions the current induced by the electrons in th e outer circuit of the chamber can be measured. If the lifetime and th e drift velocity of the free electrons in the chamber gas are known, t he collected electron-charge and therefore the deficit of negative ion s can be found. The determination of the lifetime and the drift veloci ty is achieved by analysing the decay of the induced current following a short radiation pulse.