Effects of eletromagnetic radiation of different energies in blue quartz - thermoluminescence dosimetry

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2023
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INTERNATIONAL CONFERENCE ON SOLID STATE DOSIMETRY, 20th
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Quartz, which is the second most abundant mineral in the continental crust, is found in igneous, metamorphic and sedimentary rocks, and it belongs to the silica group, which has SiO2 as its basic composition. The quartz phase presents modifications of the α and β types, being that α-quartz is stable for temperatures below 573 °C and crystallizes trigonally, and β-quartz system is stable in between 573 °C – 870 °C and crystallizes in a hexagonal structure. Its symmetry class is 32, which means it presents structural enantiomorphism. The difference in electronegativity between oxygen and silicon creates covalent bonding (40%) as well as ionic bonding (60%). The objective of this present work is to study the dosimetric properties of blue quartz such as its reproducibility, repeatability, linearity, signal fading, and energy dependence, for its possible use as a thermoluminescent dosimeter. The natural blue quartz, purchased at the LEGEP stone store in São Paulo, was pulverized with a mortar and pestle, both made of high-hardness ceramic; the sample was then sieved to select for grains measured between 80 µm and 180 µm in diameter, and grains smaller than 80 µm were used for X-ray diffraction and X-ray fluorescence. In the powder sample, measurements were done of the thermoluminescence readings of the sample in natura, as well as of the dependence of the dose to the TL response. The blue quartz grains were sensitized using two methods: heat treatment and pre-dosing, to thus obtain the best combination of synthesis temperature, sensitization dose and activation temperature. The TL glow curve of the quartz in natura shows the TL peaks, the first being around 200 °C and the second at around 325 °C. The 325 °C peak is widely used in dating works (CANO, et al., 2015; VICHAIDIS and SAEINGJAEW, 2022; GU, et al., 2021). The selected grains were separated into packages, and irradiated with increasing doses of gamma radiation from 50 Gy to 3 kGy, and, in the emission curves obtained, it is possible to observe the TL peaks around 121 °C, 169 °C, 203 °C, 257 °C and 342 °C. Peaks below 190 °C are considered unstable in dosimetry because they disappear within a few hours, and peaks above 190 °C are considered stable peaks. For the thermal treatment method, blue quartz grains were thermally treated at 400 °C, 600 °C, 800 °C, 1000 °C and 1200 °C, followed by a rapid cooling, and then irradiated with a dose of 1 Gy. It was observed that, for the temperature of 600 °C, the emission curve presents two peaks, at 150 °C and 350 °C; for 800 °C, peaks appear around 140 °C, 204 °C and 340 °C; for the thermal treatment at 1000 °C, 2 peaks can be observed at 140 °C and 200 °C, and the peak of 340 °C is not observed; and for the treatment of 1200 °C, the TL emission curve presents a well-defined peak around 204 °C. For the pre-dosing method, eight different pre-doses between 50 Gy and 20 kGy were tested, and it was found that the blue quartz sample with a pre-dose of 500 kGy has the highest TL intensity value, and, beyond that dose, the response begins to decrease. Thus, the pre-dose of 500 Gy was chosen for testing different values of thermal activation, in which the quartz grains, after being irradiated with the pre-dose of 500 Gy, were thermally treated with temperatures of 300 °C, 400 °C , 500 °C, 550 °C, 600 °C, and 650 °C for one hour, and then irradiated with a test dose of 1 Gy. It was observed that, for 550°C, the TL intensity is maximum, and, beyond that temperature, the TL intensity begins to decrease, due to thermal deactivation occurring. Blue quartz pellets have thermoluminescent properties that make them suitable for gamma radiation dosimetry. The TL emission glow curve of the material was reproduced with the GlowFit program, showing that the curve is composed of six peaks. The linearity of the TL response was proven for up to 5 Gy, and, beyond that, it then presents a sublinear behavior. The minimum detectable dose for the pellets studied is 2.34 mGy, and the TL peak at 221 °C has less than 5 % fading, indicating that this peak can be used for dosimetry. In conclusion, blue quartz pellets can be used as passive dosimeters in gamma radiation applications, and their thermoluminescent properties have been well studied and characterized.

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SILVA-CARRERA, N.B.; NILO F.C.M.; CRUZ, SOFIA P.S.; CHUBACCI, J.F.D.; WATANABE, S. Effects of eletromagnetic radiation of different energies in blue quartz - thermoluminescence dosimetry. In: INTERNATIONAL CONFERENCE ON SOLID STATE DOSIMETRY, 20th, September 17-22, 2023, Viareggio, Italy. Abstract... Disponível em: https://repositorio.ipen.br/handle/123456789/47983. Acesso em: 21 Jul 2024.
Esta referência é gerada automaticamente de acordo com as normas do estilo IPEN/SP (ABNT NBR 6023) e recomenda-se uma verificação final e ajustes caso necessário.

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