PATRICIA DE LARA ANTONIO

PATRICIA DE LARA ANTONIO

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Investigation of dosimetric properties of CaSO4:Mn phosphor prepared using slow evaporation route
2023 - SILVA, ANDERSON M.B.; RODRIGUES, DANIEL S.; ANTONIO, PATRICIA L.; JUNOT, DANILO O.; CALDAS, LINDA V.E.; SOUZA, DIVANIZIA N.
The objective of this work was to investigate the luminescent properties of CaSO4:Mn synthesized by slow evaporation route. The crystalline structure, morphology, thermal and optical properties of the phosphors were characterized by X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM), photoluminescence (PL) and thermogravimetric analysis (TGA). Moreover, using thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques, the dosimetric properties of the phosphors, such as emission spectra, glow curve reproducibility, dose-response linearity, fading of the luminescent signal, variation of the TL intensity with the heating rate, OSL decay curves, correlation between TL and OSL emissions and minimum detectable dose (MDD) were comprehensively investigated. For dosimetric analyses, the samples were irradiated with doses from 169 mGy to 10 Gy. The emission band fits with the characteristic line of the Mn2+ emission features, ascribed to 6 A1→4 T1 transition. CaSO4:Mn pellets present a TL glow curve with a single typical peak centered around 494 nm, an OSL decay curve with predominance of a fast decay component, and a MDD on the order of mGy. The luminescent signals showed to be linear and reproducible in the studied dose range. The trapping centers located between 0.83 eV and 1.07 eV were revealed for different heating rates in the TL study. The high TL sensitivity of CaSO4:Mn was proven when comparing with commercially available dosimeters. The luminescent signals exhibit a smaller fading than described in the literature for CaSO4:Mn produced by other methods.
Investigation of dosimetric properties of CaSO4:Mn phosphor prepared using slow evaporation route
2022 - SILVA, ANDERSON M.B.; RODRIGUES, DANIEL S.; ANTONIO, PATRICIA L.; JUNOT, DANILO O.; CALDAS, LINDA V.E.; SOUZA, DIVANIZIA N.
The objective of this work was to investigate the luminescent properties of CaSO4:Mn synthesized by slow evaporation route. The crystalline structure, morphology, thermal and optical properties of the phosphors were characterized by X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM), photoluminescence (PL) and thermogravimetric analysis (TGA). Moreover, using thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques, the dosimetric properties of the phosphors, such as emission spectra, glow curve reproducibility, dose-response linearity, fading of the luminescent signal, variation of the TL intensity with the heating rate, OSL decay curves, correlation between TL and OSL emissions and minimum detectable dose (MDD) were comprehensively investigated. For dosimetric analyses, the samples were irradiated with doses from 169 mGy to 10 Gy. The emission band fits with the characteristic line of the Mn2+ emission features, ascribed to 6A1→4T1 transition. CaSO4:Mn pellets present a TL glow curve with a single typical peak centered around 494 nm, an OSL decay curve with predominance of a fast decay component, and a MDD on the order of hundreds of mGy. The luminescent signals showed to be linear and reproducible in the studied dose range. The trapping centers located between 0.83 eV and 1.07 eV were revealed for different heating rates in the TL study. The high TL sensitivity of CaSO4:Mn was proven when comparing with commercially available dosimeters. The luminescent signals exhibit a smaller fading than described in the literature for CaSO4:Mn produced by other methods.
Plastic bottle caps as radiation detectors for high gamma radiation doses
2022 - OLIVEIRA, L.N.; NASCIMENTO, E.O.; ANTONIO, P.L.; CALDAS, L.V.E.
Dosimetric evaluation is indicated for material characterization seeking to identify possible applications; still, proper preprocessing techniques are critical features of this process. This work aimed to determine the linearity response of plastic samples irradiated with gamma rays using the Fourier Transform Infrared (FTIR) measurements. The plastic samples were analyzed using Derivatives and Principal Component Analysis (PCA) methods. They applied linear and Principal Component Regression (PCR) methods to obtain linearity. The methods obtained good results for linearity and also showed the evolution of each technique. In conclusion, the results indicate that the applied methods can be useful in radiation physics and for plastic samples as interesting potential radiation detectors.
Ethylene-vinyl acetate detector exposed to gamma radiation and evaluated via principal component regression
2022 - OLIVEIRA, L.N.; NASCIMENTO, E.O.; ANTONIO, P.L.; CALDAS, L.V.E.
Ethylene-vinyl acetate (EVA) is the flexible plastic material commonly used in industries. The EVA samples, in green, white and black colors were irradiated with absorbed doses of 0.01 kGy up to 10.0 kGy using a 60Co Gamma Cell-220 system, and the Fourier Transform Infrared (FTIR) spectrophotometry technique was used for evaluating the samples. This work aimed to investigate EVA samples in measurements with gamma radiation, analyzing the linearity through the Principal Component Regression (PCR) method and its sensitivity. For sensitivity and linearity, the green samples showed the best results, followed by white and black EVA samples. The PCR method inflated gradually the number of principal components, then reducing the residuals between the measured and calculated values, consequently obtaining maximum linearity of 1.000 for all of the EVA samples. In conclusion, the FTIR was adequate for the acquisition of absorbance spectra; the linearity via PCR and sensitivity showed good results indicating that the EVA detectors can be useful in radiation measurements.
Effects of manganese and terbium on the dosimetric properties of CaSO4
2022 - SILVA, ANDERSON M.B.; SOUZA, LUIZA F.; ANTONIO, PATRICIA L.; JUNOT, DANILO O.; CALDAS, LINDA V.E.; SOUZA, DIVANIZIA N.
In this study, a new CaSO4 crystal doped with manganese and terbium is described and its potential for dosimetric applications is evaluated. Crystals were synthesized using the slow evaporation route, and were prepared in pellet form with the addition of Teflon. CaSO4 was doped with manganese and terbium at a concentration of 0.1 mol% in each case. The crystalline structure and optical properties of the crystals were evaluated by X-ray diffraction, Fourier transform infrared spectroscopy and photoluminescence. The suitability of these crystals for thermoluminescent (TL) and optically stimulated luminescent (OSL) dosimetry was also investigated. The material showed adequate OSL and TL characteristics, such as a TL glow curve with two peaks at approximately 205 °C and 325 °C, an adequate OSL decay curve, good reproducibility, and linearity of the luminescent signals, when irradiated with doses of between 200 mGy and 150 Gy. Two trapping centers located at 0.77 and 1.02 eV were revealed. The heating rate dependence was also evaluated. The lowest detectable dose was investigated by the TL and OSL techniques, and the results were presented in mGy for both methods. It was also observed that co-doping with Mn and Tb contributed to a reduction in fading compared to CaSO4:Mn and CaSO4:Tb.
Evaluation of high-linearity bone radiation detectors exposed to gamma-rays via FTIR measurements
2021 - OLIVEIRA, LUCAS N. de; NASCIMENTO, ERIBERTO O. do; MORAIS JUNIOR, PEDRO de A.; ANTONIO, PATRICIA de L.; CALDAS, LINDA V.E.
In radiation physics, the study of new alternative dosimeters is of interest to the growing branch of dosimetric characterization for radiotherapy applications. The goal of this work was to expose bone samples to high doses and evaluate their linearity response to gamma rays. The Fourier Transform Infrared (FTIR) spectrophotometry technique was employed as the evaluation technique, and based on the spectrophotometry absorbance profiles the linearity was assessed based on the following methods: Area Under the Curve (AUC), Wavenumber Method (WM), Partial Component Regression (PCR) and Partial Least-Square Regression (PLSR) methods. The bone samples were irradiated with absorbed doses of 10 Gy up to 500 Gy using a 60Co Gamma Cell-220 system. The results showed, for the calibration curves of the system, adequate linearity on all methods. In conclusion, the results indicate a good linear response and therefore an interesting potential radiation detector.
Evaluation of TL and OSL responses of CaF2:Tm for electron beam processing dosimetry
2021 - ASFORA, VIVIANE K.; ANTONIO, PATRICIA L.; GONCALVES, JOSEMARY A.C.; BUENO, CARMEN C.; BARROS, VINICIUS S.M. de; OLIVEIRA, CHARLES N.P.; CALDAS, LINDA V.E.; KHOURY, HELEN J.
The thermoluminescence (TL) and infrared stimulated luminescence (IRSL) responses of in-house produced CaF2:Tm dosimeters are investigated in this work, envisaging their application in electron beam (EB) radiation processing. The irradiations were performed at an industrial EB accelerator (1.5 MeV) covering a dose rate range of 2–8 kGy/s and dose up to 10 kGy. In general, the TL glow curves display four peaks, termed as peaks 2, 3, 4, and 5, corresponding to temperatures at ~150, 200, 240, and 300 °C, respectively. The intensity of the low-temperature peaks (2 and 3) grows with the dose, while the others remain constant (saturated). Nevertheless, an evident dose effect on the glow curves manifests in decreased peak3/peak2 ratio with increasing doses. The CW-IRSL curves exhibit similar patterns with an initial signal increase, followed by an exponential decay. Instead of the normal monotonic decays, these peak-shaped curves might be due to the charge capture competition between empty shallow traps and recombination centers. Both TL and IRSL intensities increase linearly with doses up to 6 kGy, and for higher doses, they become sub-linear with a saturation trend around 10 kGy. Another common feature of TL/IRSL response is its dose rate dependence, being more sensitive at higher dose rates. Despite being dose-rate dependent, the CaF2:Tm dosimeters might be suitable for EB processing dosimetry. However, for their use as routine dosimeters, relevant dosimetric characteristics, such as fading and response reproducibility, have to be investigated. Work in this direction is underway.
Comportamento do sinal TL/OSL e PTTL/PTOSL após tratamento térmico pós-irradiação com fonte de 60Co, em amostras de LiF:Mg,Ti e CaSO4:Dy
2020 - ANTONIO, P.L.; CALDAS, L.V.E.
Materiais diferentes são utilizados em dosimetria das radiações e podem ter o seu sinal avaliado pelas técnicas de termoluminescência (TL) e luminescência opticamente estimulada (OSL). Outras formas de avaliação são feitas iluminando as amostras com luz ultravioleta (UV) antes da medição do sinal; são as técnicas de TL fototransferida (PTTL) e OSL fototransferida (PTOSL). Para tal, o material deve ser irradiado, tratado termicamente após a irradiação, exposto à luz UV e analisado com relação aos seus sinais PTTL e PTOSL. O LiF:Mg,Ti e o CaSO4:Dy são materiais dosimétricos com dados de TL e OSL já relatados na literatura. Os objetivos deste trabalho foram estudar a presença das respostas PTTL e PTOSL nestas amostras, verificar o efeito que o tratamento térmico pós-irradiação de 280°C/15 min pode causar nestas respostas, e observar se elas apresentam valores suficientes para permitir um prosseguimento destes estudos, para aplicá-las em dosimetria de doses altas. Inicialmente, as amostras foram irradiadas com 60Co (1 kGy) e analisadas com relação aos seus sinais TL e OSL. Na segunda etapa, as pastilhas foram novamente irradiadas, tratadas termicamente (280°C/15 min) e, então, tiveram medições TL, OSL e TL após a OSL, tomadas. Na terceira fase, as amostras foram irradiadas, tratadas termicamente, expostas à luz UV e avaliadas com relação aos sinais PTTL e PTOSL. Os resultados obtidos revelaram dados consideráveis e significativos para o prosseguimento dos estudos dos sinais PTTL e PTOSL das amostras.
Luminescent properties of MgB4O7:Ce,Li to be applied in radiation dosimetry
2019 - SOUZA, LUIZA F.; NOVAIS, ANDREA L.F.; ANTONIO, PATRICIA L.; CALDAS, LINDA V.E.; SOUZA, DIVANIZIA N.
MgB4O7 is a promising matrix host for use in radiation dosimetry due to its low effective atomic number (Zeff=8.2). The present work aims to investigate dosimetric and luminescent properties of the MgB4O7:Ce0,5%,Li0.5%, produced through solid-state synthesis, using the optically stimulated luminescence (OSL) technique. The first part of this work discusses the luminescent aspects of this phosphor, such as thermoluminescent emission spectra, photoluminescence emission, lifetime of emission centers and the effect of different lithium concentrations as co-dopant. In the second part, the basic OSL properties were evaluated, including dose-response curve, minimum detectable dose (MDD), step annealing, and best bleaching set-up for reuse of MgB4O7:Ce0,5%Li0.5% composites. The photoluminescence and thermoluminescence emission spectra of the composites present an emission peak at UV-VIS range centered around 370 nm, which is the most suitable for OSL dosimetry; this emission is related to Ce3+ electronic transitions and has a luminescence center lifetime of 0.003 ms. From the step-annealing analyses, it can be seen that the OSL emission is related to different depth trap centers in the band gap. The OSL dose-response curve is linear from 0.1 Gy to 100 Gy, with a MDD around 1 mGy. These properties make this material a strong candidate for different applications in radiation dosimetry field.
Evaluation of the thermally and optically stimulated response of an Italian Obsidian irradiated in 60Co beams
2019 - ANTONIO, PATRICIA L.; OLIVEIRA, RAQUEL A.P.; KHOURY, HELEN J.; CALDAS, LINDA V.E.
From Obsidian silicate, in its natural form, pellets were manufactured adding Teflon to the material in powder. These pellets were exposed to the gamma radiation beams of a 60Co source in a dose interval from 10 Gy to 10 kGy. The Obsidian in powder was investigated in relation to its physical and chemical characteristics, by means of the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. After the irradiation procedure, the signal of the samples was evaluated by means of three techniques: thermoluminescence (TL), optically stimulated luminescence (OSL) and thermally stimulated exoelectron emission (TSEE). The objective of this work was to verify the TL, OSL and TSEE response of the Obsidian+Teflon pellets after exposure to high doses of gamma radiation. Different response characterization tests were performed, as TL and TSEE emission curves, OSL signal decay, reproducibility, dose-response curves, lower detection limits and fading. From these results, it can be observed that the Obsidian+Teflon pellets present good conditions to be used as high dose gamma radiation detectors; the results obtained with the OSL technique were the most adequate in terms of response in function of absorbed dose. The fading of the signals, varying from about 26% (TSEE) to 44% (OSL), in a time interval of 360 h post-irradiation, also showed favorable results for the use of this material as radiation detector, when the measurements are taken after a defined time interval.