Characteristics of a radiation-charged electret dosimeter

The radiation-charged electret ionization chamber uses an electret formed in situ by applying a bias voltage to the chamber electrodes while the chamber is being irradiated with X-rays. An electrometer permits measurement of the charge on the electret surface before and after the use of the chamber as a dosimeter. The authors present measurements of dosimeter range, sensitivity and energy dependence as functions of bias potential, electrode separation, guard ring size and various materials. Reproducibility permits detection as low as 80 μGy, with range to ~5 Gy, depending on the design of the chamber, with charge retention properties similar to electrets formed isothermally from corona discharge