SURFACE-CHARGE DISTRIBUTION DURING THE CHARGING AND DISCHARGING OF ELECTRETS PRODUCED IN ELECTRET IONIZATION CHAMBERS

Spatial charge distributions during the charging and discharging processes of thin film polymer electrets produced by ionizing radiation in air are presented. The charge distributions were measured for various externally applied potentials and air gap thicknesses of electret ionization chambers (EIC). The results show important limitations in charging electrets with this technique in EIC of relatively large air gaps, but show excellent results with EIC of small air gaps. Practical problems of achieving maximum charge densities corresponding to the externally applied potential are discussed. The change in charge distributions during the charging and discharging stages with various external potentials and air gaps are also presented and analyzed, and possible causes for the patterns are given. Measurements of charge distributions during discharge describe the neutralization process involved in EIC, and suggest limitations to the practical size of chambers. Linearity of EIC response to exposure and changes in the size of chamber sensitive volume due to field distortions are also discussed.