Evaluation of doses in radiotherapy using solid-state composites based on natural colourless topaz

Thermoluminescent composites of sintered synthetic-topaz/in situ corundum for dosimetry by a novel reversible process

Topaz (Al2F1·44(OH)0·56SiO4)/corundum (Al2O3) composites were prepared by a facile and novel reversible process from the sintering of synthetic topaz and AlF3 powders, with corundum formed in situ into the topaz matrix. The corundum formation reaction occurs in the temperature range 875-975 °C, from 40 min sintering time, obtaining the topaz- Al2F1·44(OH)0·56SiO4/corundum- Al2O3 composites. Although sintering temperature and time increment lead to higher corundum formation in the topaz matrix (78.4 wt % Al2O3 at 975 °C for 60 min), longer residence times give place to corundum percentage decrease due to topaz reconversion. The composites' microstructure is characterized by a rectangular bar with stacked pyramidal ends and polycrystals of hexagonal plates for topaz and corundum, respectively. For the topaz/corundum composites, the maximum density was 3.05 g/cm3 (17 % porosity) for specimens sintered at 925 °C for 20 min. The glow curves of the topaz/in situ corundum composite sintered at 975 °C and 0 min dwell time show thermoluminescent peaks between 180 and 250 °C, useful for dosimetric applications. The most helpful peak (at 221 °C) in the topaz/corundum composite's glow curves determined by computational deconvolution is sharp and exhibits the highest thermoluminescent response. Dose-response analysis of the composite (sintered at 975 °C for 0 min) with the best thermoluminescent response revealed two ranges of linear behavior, the first from 2 to 200 mGy, with an adjustment of 99.9 % and the second in the range 5-300 Gy (99.8 % fitting). The thermoluminescent response improvement of the topaz/corundum composites is attributed to the corundum formed in situ during sintering. Fading rate studies of the composite with the best sintering treatment revealed a signal decrease of 4 % after 15 days, which remained constant for up to 30 days, and 8 % after 60 days. The kinetic parameters, kinetics order (b), activation energy (E), and frequency factor (s) determined using the glow peak shape method showed second-order kinetics. The topaz/corundum composite with the best TL response (975 °C, 0 min) presents an effective atomic number (Zeff) of 11.74. The detection of lower doses (mGy) and the linear response at higher doses (Gy) of beta 90Sr, together with the other thermoluminescent properties, suggest that the topaz/corundum composites sintered at 975° for 0 min dwell time may find application in radiotherapy, geological dating, and environmental dosimetry.

TL behavior of topaz-glass composite in various irradiation fields

Topaz is a natural hard silicate mineral that has the potential to be used as a thermoluminescent dosimeter (TLD). It is difficult to manufacture chips of topaz and problematic to use its powder as TLDs. Topaz-glass composite (in the form of pellets) can be made easily and applied for radiation dosimetry. To produce pellets of topaz-glass composite in 2:1 wt (%), topaz powder was combined with commercial glass. The pellets with 6 mm diameter and 1 mm thickness were sintered in a furnace at 900°C for 1 h. The composite pellets were irradiated with x-ray and gamma photons and alpha and beta particles. The pellets yielded two peaks in the glow curve; Peak 1 at temperature range 150-160°C and Peak 2 at 250-260°C. The intensity of Peak 2 rose linearly with the increase in absorbed dose. The intensity of Peak 2 was comparable with peaks for photons and beta irradiation but relatively low for alpha exposure. The reproducibility of the intensity of Peak 2 was within 5-8%. Two months after irradiation of the pellets, the fading of the intensity of Peak 2 was found to be about 7%. The topaz-glass composite can be used effectively and efficiently for dosimetry of alpha, beta, and gamma radiation.