Temperature and temporal dependence of the optical response for a radiochromic dosimeter

Abstract

Both temporal and thermal dependencies of the dose response have been observed in radiochromic dosimeters. As these dependencies may be influenced by the dose level, the present study investigates the temperature dependence during irradiation and the temporal change of the optical response following irradiation of radiochromic dosimeters at a range of doses. Cuvette samples of the PRESAGE™ radiochromic dosimeter were irradiated within a dose range of 0-10 Gy at irradiation temperatures within 5-35 °C and postirradiation storage within 6-30 °C. The optical response due to irradiation was measured using a standard spectrophotometer and the data were analyzed in terms of thermal and temporal change. The initial dose response was linear over the applied dose range independent of irradiation temperature. However, the optical response to a specific dose increased exponentially with irradiation temperature corresponding to an activation energy of 0.114 ± 0.007 eV. The temporal change in dose response after irradiation consisted of an offset, an auto-oxidation rate with activation energy 0.84 ± 0.03 eV, and an initial exponential increase in optical response (1.6 ± 0.2 eV) followed by an exponential decrease in optical response (0.98 ± 0.08 eV). These contributions depended on both storage temperature and the dose given, leading to a nonlinear dose response with time at low storage temperatures and a high auto-oxidation rate at high storage temperatures. Thermal equilibration is important to the radiochromic dosimeter investigated due to an exponential change in dose response with irradiation temperature and a considerable postirradiation temporal change in response. For the dosimeter version investigated in this study, a compromise in storage temperature has to be made between increasing the nonlinearity of the dose response with time and inducing a high auto-oxidation rate.