Abstract
Aims: CaSO4 doped with one or two rare earth elements dysprosium (Dy) and thallium (Tm) was studied using thermoluminescence (TL) technique with different annealing temperatures and different concentrations. Study Design: In the present paper, stored and fresh sample synthesis effects on the kinetic parameters of dosimetric peaks were investigated. Place and Duration of Study: Department of Physics (Atomic Physics Lab's, The University of Jordan), between July 2013 to August 2016. Methodology: The preliminary studies TL properties of synthesis doped and co-doped samples with different concentrations and annealing temperatures, actual samples experiment and an analysis of results. Samples saved three years to study the effect of storage on the TL properties of samples. The experimental samples were divided into three groups. Results: This paper gives the account of the development of a new and sensitive phosphor CaSO4: Dy,Tm and its characterization. The standard production procedure based on the re-crystallization method was used to prepare CaSO4: Dy, Tm. The TL-studies were carried out by exposing it with 1rad of beta radiation (90Sr-90Y-source). The theoretical studies to determine the number of peaks and kinetic parameters related to the TL glow peaks in CaSO4:Dy,Tm was performed using the computerized glow curve de-convolution (CGCD) method. Experiments were performed to determine optimum concentration of the dopants Dy and thallium Tm in the host CaSO4 so that maximum sensitivity of the phosphor may be achieved. The optimum dopant concentration turned out to be 0.2 wt%. As there were two dopants Dy and Tm their relative ratio were varied the concentration of total dopant (Dy and Tm). General-order kinetics formula with a two and three energy levels of traps was adopted as the fitting function. Conclusion: The results indicate that both stored and fresh samples have pronounced influence on the kinetic parameters. In the storage times experiments, change in traps distribution due to diffusion at room temperature may be the main reason causing the variations in activation energies. In the different sources experiments, different spatial distributions of trapped charge carries due to the different photoelectric effect of different photon energies may influence the binding energies. Other factors such as trapped charge conversion from one type of trap to another, competing non-radiation defect interaction and different photon energies may be used for interpreting the drift phenomenon of activation energies. Temperature dependence of frequency factor, variations of temperature lag and fluctuation and shift of the distribution frequency factor can be used to interpret the drift phenomenon of frequency factor. Kinetic order variation during the heating stage can also be used to interpret the drift phenomenon of kinetic order.