Improvement of the CTA dosimetric properties by the selection of readout wavelenght and the calculation of the spectrophotmetric quantity

A detailed study was performed on sources of uncertainty associated with the measurement of cellulose triacetate (CTA) film dosimeter response at high absorbed doses. The results show a significant dependence of the uncertainty on the selected readout wavelength in the range 269–290 nm, as well as the spectrophotometric quantity used for calculating the response. Two different calculated quantities were used, the more familiar one being the radiation-induced change in absorbance (δA)λ=(Aλ−Ao)λ, of the film, for absorbance values before (Ao) and after irradiation (Ai), and the other the ratio (Ai/Aoλ at a given wavelength. The effects of temperature, dose rate and r.h. of the surrounding atmosphere during and after irradiation on dosimeter performance, at some selected UV wavelengths of analysis e.g. λ = 274,280 and 290 nm, were examined. Post-irradiation stability at different humidities was also studied. Improved environmental dependencies and dosimetric response properties were achieved by selecting the quantity (Ai/Ao)274 nm.