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Thermoluminescence (TL) dosimetry is used in radiation protection and for measuring absorbed dose to patient in diagnostic radiology and radiotherapy. The main aim of the study herein was to determine the TL properties of BaSO₄:Eu nanophosphors following irradiation with g- and X-rays as well as low energy protons.

BaSO₄ phosphors activated with various concentrations of Eu were prepared by co-precipitation method. The highest sensitivity was obtained for an Eu  concentration of 0.5 mol%. For studying the dependence of TL output on radiation quality, powder samples of about 10 mg were irradiated with Co-60 g-rays (reference quality), 15.2 MeV protons, and 100 to 225 KV X-rays. Absolute dosimetry was ensured with ion chambers. The TL was recorded with different heating rates like 5, 10, 15 and 20 K/s. The TL dose response, glow curve structure and shape, reusability, fading and the radiation quality dependence were consequently studied.

TL glow curve of optimized BaSO₄:Eu irradiated with doses up to 1 Gy display a major peak at ≈ 225 °C. Thus, the given nanophosphor has a reasonably simple glow curve structure which can be attributed to a simple distribution of the luminescence traps. Dose-response analysis over the dose range 0.2-1 Gy showed that the response of g-irradiated samples was 1.7 times higher than following proton irradiation (Figure 1). Irradiation with 100, 160 and 225 kV X-rays gave approximately 40 times higher response compared to g-irradiation. The reusability test for was performed for ten consecutive reading and annealing cycles of the same samples irradiated with X-rays in each cycle.  The TL intensity showed a slight decrease after the first cycle and then stabilized. The TL signal fading measurement was performed for g-irradiated samples over 50 days storage in dark atmosphere. During this period 7 % of TL signal loss was observed.

Figure 1. TL intensity versus dose for BaSO₄:Eu dosimeter following g – or proton – irradiation.

The radiation quality dependence study shows that the TL output per dose to water of the BaSO₄:Eu  nanophosphor is dependent on radiation type (g-rays vs protons) and photon energy (g-rays vs X-rays). The strong X-ray energy dependence may be explained by the high mass energy absorption coefficient of the BaSO₄ compound. However, the simple glow curve structure, excellent reusability and low fading indicates favorable properties for dose determination in radiotherapy, as long as the samples are calibrated in the user beam.