Effect of Thermal Treatments on the Glow Curve and Stability of CaSO₄:Dy for Radiation Dosimetry Applications

Abstract

A comprehensive investigation was carried out into the optimisation of Dysprosium-doped Calcium Sulphate (CaSO₄:Dy) for high-precision thermoluminescence (TL) dosimetry through controlled post-synthesis thermal annealing. By comparing samples annealed at 600°C and 900°C, we demonstrate that high-temperature treatment is a critical step in the material's physical and dosimetric properties. Structural analysis via X-ray diffraction confirmed the phase purity of the orthorhombic anhydrite structure in both samples. However, scanning electron microscopy revealed that the 900°C anneal induces significant microstructural evolution, promoting substantial grain growth and refining the phosphor's morphology, while energy-dispersive X-ray analysis verified a consistently uniform Dy³⁺ distribution. The 600°C sample exhibits a complex, multi-component glow curve with a prominent, low-temperature peak (~160°C) and a main dosimetric peak (~250°C). In contrast, the 900°C annealing process effectively eliminates the shallow trap corresponding to the 160°C peak, yielding a clean, single, and highly stable dosimetric peak. This suppression of the unstable, low-temperature signal is paramount for minimising thermal fading and ensuring long-term dosimetric accuracy. To elucidate the underlying trap kinetics, a Computerized Glow Curve Deconvolution (CGCD) was performed using a probability-based general-order model. The analysis revealed that annealing at 900°C fundamentally reconfigures the material's defect structure, favouring the formation of deeper, more thermally stable traps and significantly reducing the probability of charge carrier retrapping.