X and Gamma Dose Measurement Using Electrets

Abstract

A Teflon electret of 5 cm diameter loaded into a perspex chamber of 63 ml formed a simple electret dosemeter. Such a dosemeter showed a decrease of charge which was linear with dose (like an ionisation chamber) over a certain range of charge of the electret. The measured change in charge was used to calculate the dose received by the dosemeter. The calculated value agreed well with the actual dose received by the dosemeter. Using an electret of 0.31 cm thickness, the dosemeter could cover a range of 5.6 mGy (560 mrad) with a resolution of 0.004 mGy (0.4 mrad). The performance was found to be independent of photon energy and dose rate. Such dosemeters are particularly useful for long-term measurement of dose because of the permanent nature of the dose information retained by the electret, and also due to their insensitivity to variations in temperature and relative humidities normally encountered in the environment. The paper describes a liquid contact method for preparation of electrets. The details of a capacitive probe method for measurement of charge are given and a set of theoretical expressions needed for designing a dosemeter to meet a particular requirement are also presented.