IMPROVEMENT OF THE CTA DOSIMETRIC PROPERTIES BY THE SELECTION OF READOUT WAVELENGTH AND THE CALCULATION OF THE SPECTROPHOTOMETRIC QUANTITY

A detailed study was performed on sources of uncertainty associated wi th the measurement of cellulose triacetate (CTA) film dosimeter respon se at high absorbed hoses. The results show a significant dependence o f the uncertainty on the selected readout wavelength in the range 269- 290 nm, as well as the spectrophotometric quantity used for calculatin g the response. Two different calculated quantities were used, the mor e familiar one being the radiation;induced change in absorbance (Delta A)(i) = (A(i) - A(o))(i), of the film, for absorbance values before ( A(o)) and after irradiation (A(i)), and the other the ratio (A(i)/A(o) )(i) at a given wavelength. The effects of temperature, dose rate and r.h. of the surrounding atmosphere during and after irradiation on dos imeter performance, at some selected UV wavelengths of analysis e.g. l ambda = 274, 280 and 290 nm, were examined. Post-irradiation stability at different humidities was also studied. Improved environmental depe ndencies and dosimetric response properties were achieved by selecting the quantity(A(i)/A(o))(274nm).