Dosimetric properties of thermoluminescent pellets of CaSO4 doped with rare earths at low doses

Abstract

Thermoluminescent dosimeters are widely used in radiation dosimetry, including low dose applications such as personal dosimetry. This work aimed to manufacture thermoluminescent pellets using CaSO4:Tm; CaSO4:Dy,Tm; CaSO4:Dy, Tb and CaSO4:Dy, Eu phosphors and to study their dosimetric properties in comparison to commercially available CaSO4:Dy (TLD-900). The phosphors were synthesized by the slow evaporation route using a solution of sulfuric acid, calcium carbonate and the dopants. The pellets were manufactured using Teflon as aggregate agent. The glow curves of the different pellets were measured and the integral of the dosimetric peak was used as the dosimetric response for each material. The dose-response curves were measured in a dose range of 100 μG y to 50 mGy by 137Cs (γ-source) and X-rays (30 kVp up to 120 kVp). The energy dependence and fading of the pellets were also studied. Groups of 30 pellets were used to investigate the response homogeneity for the studied materials. The glow curves for all the studied materials (excluding CaSO4:Eu) showed the maximum luminescent emission at around 260 °C, but with different intensities. The CaSO4:Tm pellets showed the highest thermoluminescent emission among the studied materials. All the materials showed a linear response in the studied dose range, with CaSO4:Tm pellets showing the highest sensitivity at all radiation qualities. The highest energy dependence was found for the ISO N-40 beam quality (40 kVp X-rays) for all materials when compared to irradiations by the 137Cs source. A 7.7% fading for the CaSO4:Tm was found for a period of two months. All the manufactured pellets showed better dosimetric properties than the studied standard CaSO4:Dy.