MODELING OF SURFACE-CHARGE DISTRIBUTIONS IN ELECTRET IONIZATION CHAMBERS

ComPuter modeling of the change of electret surface-charge distributio n within electret ionization chambers (EIC) during the electret chargi ng and discharging processes are described. Assuming a uniform and con stant rate of ion generation, the theory of ion recombination in air i s applied to Laplace's equation to develop a description of the rate o f charge accumulation and surface charge distribution. It is shown tha t distortions of electric fields within the air gap of the EIC control the distribution of charge accumulation, while saturation conditions, that determine the level of recombination of charges within the air g ap of the EIC, control the maximum potential that can be deposited ont o the electret surface. Results of modeling are compared with measured data, and suggestions for refinement in the model are discussed.