CaSO₄:Tm thermoluminescent semi-spherical-shaped pellets for improved angular dependence dosimeters

The angular dependence of thermoluminescent (TL) pellets can present a challenge in thermoluminescent dosimetry (TLD), especially at personal dosimetry applications. In this work, semi-spherical-shaped pellets of CaSO₄:Tm were produced to evaluate their potential use in personal dosimetry with improved angular dependence in comparison to the conventional cylindrical-shaped pellets. Pellets with approximately 27 mg were produced with 2:1 proportion in mass of polytetrafluoroethylene (PTFE) to phosphor to optimize its physical resistance and handling properties. Doses ranging from 0.5 mGy to 50 mGy from ¹³⁷Cs radiation source were used to study the pellets sensitivity. Results show that the produced pellets exhibit the dosimetric peak at ∼300 °C and a lower intensity peak at ∼200 °C. The dose-response curve for the semi-spherical-shaped pellets showed a linear behavior for the studied dose range. The sensitivity was (58.8 ± 2.0) nC/mGy and the lower detection limit was (0.037 ± 0.001) mGy. All samples showed a good reproducibility (coefficient of variation less than 10%). In comparison with CaSO₄:Tm cylindrical pellets, the semi-spherical-shaped pellets exhibited better angular dependence for angles up to 90°. The maximum difference between the irradiation at 0° and the other angles was only 4.6% for the semi-spherical-shaped pellets and 32% for the cylindrical pellets. Preliminary results suggest that the produced semi-spherical-shaped pellets based on CaSO₄:Tm (2:1) are suitable as TL detectors in personal monitoring.