Charge transport and storage in the radiation-charged electret ionization chamber

Abstract

Numerical calculations of time‐dependent charge distributions are presented and compared with distributions measured on radiation‐charged electrets made of thin polymer films, which are charged and discharged in a radiation‐charged electretionization chamber (REIC) through the application of ionizing radiation. The chamber resembles a parallel plate ionization chamber, and has a thin film of polymer covering the collector and guard‐ring electrodes. Calculations are performed by solving Laplace’s equation for the true geometry of the charging/discharging set‐up, then applying estimates of ion‐density distributions generated from known scattering distributions and/or simpler approximations. Measurements of radiation induced conductivity (RIC) are presented and fitted to an empirically derived analytical model, and the effects of RIC on the operation of a radiation dosimeter based on the electret are investigated and discussed. Short‐term and long‐term charge decay from the electret is measured and fitted to a previously developed model. The effects of post‐charging heat treatment of the radiation‐charged electret are presented and discussed. Last, the dosimetric characteristics of the REIC are considered in light of those physical aspects investigated here.