The Dose-Rate Response of a Dye-Polychlorostyrene Film Dosimeter

The response of dye-polychlorostyrene film dosimeters are compared at low (~103 rad/sec) and high (~1015 rad/sec) dose rates. Low dose rate exposures were obtained with a 60Co gamma-ray pool source, and high dose rates were obtained with a high-intensity, pulsed electron source. The dosimeter is a solid solution of polychlorostyrene and malachite green methoxide which changes color upon irradiation. Two broad absorption peaks appear in the visible region with maxima at about 425 and 625 nm. The change in optical density of the 625-nm peak was monitored and correlated to the absorbed dose received by the dosimeters. At low dose rates, the source output was determined on the basis of a previous calibration with a carbon calorimeter and a cavity ionization chamber; at high dose rates, a thin dosimeter calibration system was employed. The calibration system has as its primary measuring elements aluminum calorimeters whose temperatures after exposure were monitored by chromel-constantan thermocouples. Associated electronics recorded the outputs of the thermocouples at every 0.1 sec. In the two cases, the dosimeters were exposed in a different but homogeneous medium, carbon or polystyrene at the low dose rates and aluminum at the high dose rates. In addition, Monte Carlo calculated stopping power ratios of the dye-film dosimeter to the medium were required to interpret the dose received by the dosimeters. The results indicate that there is no significant difference in the response at the two different rates.