Space charge effects in ionization type particulate detectors

The response to particulates of an ionization chamber with adjacent unipolar and bipolar zones is analyzed. Values of reduced ion mobility from particulate charging in the unipolar zone and the resulting increase in surface recombination in the bipolar zone are determined from experimental data. A solution of the general field equation as a function of distance in parallel plate geometry is plotted. The current–voltage characteristic from the general equation is compared with that from the simpler vacuum field approximation for bipolar volumes. The close agreement warrants general use of the vacuum field in ionization chambers for the small operating current densities employed in these detectors.