Field test of electret ion chambers for environmental monitoring

A field test of electret ion chambers was performed to evaluate their performance in making environmental exposure measurements at nuclear facilities. The objectives of the study were to determine electret ion chamber variability and to perform comparisons with thermoluminescent dosimeter and high-pressure ion chamber measurements. Three electret ion chambers were placed at each of 40 monitoring locations in the vicinity of a commercial nuclear power station during four consecutive quarters. The electret ion chamber measurements were compared to thermoluminescent dosimeter measurements made by the Nuclear Regulatory Commission and the South Carolina Department of Health and Environmental Control. Two types of comparison were made with the high-pressure ion chamber. One used yearly average electret ion chamber measurement and instantaneous high-pressure ion chamber measurements at 15 of the monitoring locations. The other involved the simultaneous exposure of five electret ion chambers and the high-pressure ion chamber for 15 d at a single location. The mean ratios of electret ion chamber measurements to thermoluminescent dosimeter measurements was 1.06. The mean ratio of electret ion chamber measurements to instantaneous and simultaneous high-pressure ion chamber measurements were 1.06 and 1.07, respectively. Electret variability, defined here as the ratio of the standard deviation to the mean, was determined for each set of three detectors. The average variability for the 160 sets of quarterly measurements was approximately 7%. Among the 450 individual electret measurements, there were six outliers. Based on the results of this study, electret ion chambers appear to yield accurate measurements of environmental exposure provided that measures are taken to either minimize or correct for radon interferences and care is taken to prevent spurious discharges during handling.