Behaviour of CaSO4:Dy embedded teflon discs at high annealing temperatures

The behaviour of CaSO4:Dy embedded Teflon (PTFE) thermostimulated luminescent dosimeters (TLDs) at high annealing temperatures (500-800 deg. C) has been studied for the first time. The study reveals the complete evaporation of Teflon at annealing temperatures above 500 deg. C. The residual powder weighed only half that of the CaSO4:Dy powder contained originally in the disc. X-ray diffraction study indicates that this is due to the conversion of CaSO4 to CaF2 and DyF3 during the breakdown of Teflon polymer. As a result, the weight and TL sensitivity of the residual powder, say after a 700 deg. C, 1 h annealing treatment, were only 50 and 29% respectively of that of the virgin CaSO4:Dy phosphor powder of similar grain size