SILAS CARDOSO DOS SANTOS

SILAS CARDOSO DOS SANTOS

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Correlation between zeta potential and electron paramagnetic resonance of thulium, europium co-doped yttria based suspensions
2024 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
The formation of advanced ceramic components with homogeneous microstructure and functional characteristics demands a suitable control of particle dispersion. Thus, the characterization of particle stability as immersed in a liquid medium is important. The present paper reports an approach to evaluate the stability of europium, thulium co-doped yttria (YET) nanoparticles by a correlation between zeta potential and Electron Paramagnetic Resonance (EPR) techniques. Based on results, YET suspensions exhibited high stability apart from pH 10, while their isoelectric point presented a slight variation from pHIEP 8.5 to 9.2 according to thulium content 0 and 2 at.%, respectively. The peak-to-peak amplitude of EPR spectra of the YET suspensions increased as pH shifted toward alkaline condition, following zeta potential curves features. The present achievements are very useful parameters to form stable suspensions based on rare-earth oxides and to advance toward new materials for radiation dosimetry.
Building up europium thulium co-doped yttria nanoparticles with electron paramagnetic resonance response by colloidal synthesis
2023 - SANTOS, SILAS C. dos; RODRIGUES JR., ORLANDO; CAMPOS, LETICIA L.
In the radiation dosimetry field the research for new materials is a continuos demand with the aim to provide highly improvement procedures where ionizing radiation is used. Considering this challenge, the present work reports the colloidal synthesis of europium-thulium-co-doped yttria powders (YET) and evaluates the dopants effect on the promotion of EPR response of yttria. The powdered compositions prepared with up to 2at.%Tm and 2at.%Eu (at.%, atomic percentage) were evaluate by XRD, PCS, SEM, and EPR. Based on the results, the proposed synthesis method provided ceramic powders with cubic C-type form and mean particle size (d50) less than 160nm. The most significant EPR dose-response was noticed for the powdered composition prepared with 0.5at. %Tm (YET0.5) as irradiated with 5kGy (60Co). These findings are key parameters to advance toward the formation of new materials for radiation dosimetry.
A glance at dysprosium oxide free powders
2023 - SANTOS, SILAS C.; RODRIGUES JUNIOR, ORLANDO; CAMPOS, LETICIA L.
Background: Dysprosium oxide (Dy2O3) gathers a set of profitable properties with a wide range of applications, including energy and astronomy. Particular characteristics directly influence the formation and features of materials by colloidal processing. The main purpose of this paper is to carry out a powder characterization of Dy2O3particles. The findings reported are worthwhile parameters to advance in the formulation of new smart materials for radiation dosimetry. Methods: Dy2O3 powders were characterized by XRD, PCS, SEM, pynometric density (ρ), FTIR, ICP, EPR, and zeta potential (ζ). Results: The powdered samples exhibited as main features a cubic C-type structure following the RE-polymorphic diagram, a mean particle size distribution with d50 of 389nm, and pynometric density of 7.94g.cm-3. The EPR spectra revealed three distinct peaks, p1, p2, and p3, with the following g values: 2.3121, 2.1565, and 2.1146. In addition, the nanoparticles presented high stability at pH 5.5 and a ζ-value of |49.7|mV. Conclusion: The powder characterization of Dy2O3 powders was reported. The results achieved in this study may be considered worthwhile parameters to advance in the formulation of Dy2O3- based materials for radiation dosimetry.
Synthesis of thulium-yttria nanoparticles with EPR response
2022 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
Approaches to form new materials for radiation dosimetry are essential to enhance quality assurance and quality improvement practices based on radiation protection concept. The present work reports a hydrothermal synthesis based on a relative low temperature and pressure to form thulium-yttria nanoparticles with electron paramagnetic resonance response. Thulium-yttria nanoparticles were prepared and characterized by XRD, SEM, PCS, and EPR. According to results, the hydrothermal method provided thulium-yttria nanoparticles with cubic C-type structure, mean particle size (d50) less than 160nm, and EPR response. The EPR spectra of powders exhibited two resonance peaks p1 and p2 recorded at 350 and 160mT, respectively. The enhancement of the EPR response of yttria by the use of thulium as a dopant provide meaningful parameters to advance in the formation of new rare earth-based materials for radiation dosimetry.
Evaluation of rare-earth sesquioxides nanoparticles as a bottom-up strategy toward the formation of functional structures
2022 - SANTOS, SILAS C. dos; RODRIGUES JUNIOR, ORLANDO; CAMPOS, LETICIA L.
Background: The strategy to form functional structures based on powder technology relies on the concept of nanoparticles characteristics. Rare-earth sesquioxides (RE2O3; RE as Y, Tm, Eu) exhibit remarkable properties, and their fields of application include energy, astronomy, environmental, medical, information technology, industry, and materials science. The purpose of this paper is to evaluate the characteristics of RE2O3 nanoparticles as a bottom-up strategy to form functional materials for radiation dosimetry. Methods: The RE2O3 nanoparticles were characterized by the following techniques: XRD, SEM, PCS, FTIR, ICP, EPR, and zeta potential. Results: All RE2O3 samples exhibited cubic C-type structure in accordance with the sesquioxide diagram, chemical composition over 99.9 %, monomodal mean particle size distribution, in which d50 value was inferior to 130 nm. Among all samples, only yttrium oxide exhibited an EPR signal, in which the most intense peak was recorded at 358mT and g 1.9701. Conclusion: Evaluating nanoparticle characteristics is extremely important by considering a bottom-up strategy to form functional materials. The RE2O3 nanoparticles exhibit promising characteristics for application in radiation dosimetry.
Colloidal processing of thulium-yttria microceramics
2022 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
The development of new dosimetric materials is essential for the safe and effective use of nuclear technology. In the present study, an eco-friendly bio-prototyping approach was developed for preparing thulium-yttria microceramics with potential applications in radiation dosimetry. Micro-powder compacts were obtained by casting colloidal thulium-yttria suspensions prepared with 20 vol% particles in thin-walled tube templates. Samples were sintered at 1600 °C for 2 h under the environmental pressure and atmosphere to obtain thulium-yttria microceramics with dimensions of 3.33 ± 0.01 mm × 2.27 ± 0.01 mm (height × diameter), as well as a cubic C-type structure, pycnometric density of 4.79 g cm−3 (95.61% theoretical density), and surface microstructure comprising hexagon-like grains bonded at the boundaries. The use of thulium as an activator of yttria greatly improved the electron paramagnetic resonance (EPR) response of the microceramics, where the main EPR peak (p1) was recorded at 351.24 mT and the g factor was 2.0046. The innovative findings obtained in this study may facilitate the production of new solid state dosimeters.
Towards a new promising dosimetric material from formation of thulium-yttria nanoparticles with EPR response
2021 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
Advances toward new materials for dosimetry application is essential to enhance quality assurance and quality improvement practices based on radiation protection concept. Face to this challenge the present work reports an approach to produce thulium-yttria nanoparticles with electron paramagntic resonance response by an alternative hydrothermal synthesis based on a relative low temperature and pressure. Distinct compositions of thulium-yttria nanoparticles with up to 2 at.%Tm (at.%, atomic percentage) were prepared and characterized by XRD, SEM, PCS, and EPR. The proposed synthesis method followed by thermal treatment of the precursor powder at 1100 ◦C for 2 h provided thulium-yttria nanoparticles with rounded shape, cubic C-type structure, and mean particle size (d50) less than 160 nm. Among all compositions formed, thulium-yttria nanoparticles prepared with 0.1%Tm presented the most remarkable EPR response. The production of fine thulium-yttria nanoparticles with EPR response supply meaningful parameters to advance in the formation of new dosimetry materials based on rare earths.
Formation and EPR response of europium-yttria micro rods
2019 - SANTOS, SILAS C. dos; RODRIGUES JUNIOR, ORLANDO; CAMPOS, LETICIA L.
Designing new materials with suitable dose-response efficiency is a great challenge in radiation dosimetry search. Yttria (Y2O3) has excellent optical, mechanical, chemical, and thermal properties. Besides, yttria exhibits crystal characteristics that provide insertion of other rare earths, forming innovative materials. Nevertheless, there are quite few studies on formation, microstructural and EPR response evaluation of yttria. This work reports the formation and EPR characterization of europium-yttria micro rods for radiation dosimetry. Ceramic rods obtained by sintering at 1600ºC/4h in air were exposed to gamma radiation with doses from 1Gy to 150kGy. Particle, microstructural and dosimetry characterizations were performed by PCS, XRD, SEM, OM, and EPR techniques. As sintered europiumyttrium rods exhibited dense microstructure (90% theoretical density) and linear EPR dose response behavior up to 10kGy. These results show that europium-yttria is a promising material for radiation dosimetry.
Stability study of the alanine epr dosimetry system at IPEN/CNEN SP
2019 - RODRIGUES JR ., ORLANDO; SANTOS, SILAS C. dos
The dosimetry system using alanine EPR is a standard secondary calibration system for high doses. IPEN's High Doses Dosimetry Laboratory (LDA) has an Electron Paramagnetic Resonance equipment operating in the X band which performs high dose dosimetry service for electron and X ray fields for the dose range of 10Gy to 200kGy. IPEN has established a dosimetry system based on an alanine dosimeter developed at the institute. The system is composed of pure DL alanine encapsulated in a polyethylene microtube, which allows estimated doses of 10Gy to 200kGy. The advantages of this system are the low signal fading over a long period of time (over 90 days) and dose measurements above 150kGy. The main disadvantage is the difficulty in measures below 10Gy. In order to improve quality assurance services delivered in radiotherapy, commercial alanine dosimeters are being tested and compared with the already established system for measurements with time intervals longer than 90 days. The present work is an evaluation of the commercial L alanine dosimeter signal compared to the alanine dosimeter produced in IPEN. The dosimeters were irradiated with X ray and E beam and doses of 1, 10 and 20Gy. All measurements were performed following the same laboratory protocol based in ISO/ASTM guidelines. Environmental effects such as temperature, sensitivity to light and air humidity, and other storage conditions were evaluated. The results show that the decay of commercial dosimeters over 36 months was 11% higher than that observed in the dosimeter developed in IPEN, indicating the need for a correction factor for the comparison of dosimetry systems.
Synthesis, processing, and electron paramagnetic resonance response of Y1.98Eu0.02O3 micro rods
2018 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
Innovating dosimetric materials, which includes design and development of new dosimetric materials based on rare earth oxides, is challenging. Yttrium oxide (Y2O3) is one of the most important sesquioxides and presents crystal characteristics that enable doping with rare earth ions, making it a promising material for radiation dosimetry. This paper reports on the development and measurement of Electron Paramagnetic Resonance (EPR) signal response for Y1.98Eu0.02O3 micro rods that have undergone facile low-pressure hydrothermal synthesis and bio-prototyping. Assynthesized powders with narrow sub-micrometer particle size distribution with d50 of 584 nm exhibited a reactive surface, which led to the formation of stable aqueous suspensions by controlling the surface charge density of particles through alkaline pH adjustment. Ceramic samples with dense microstructure were formed by sintering at 1600 ºC for 4h at ambient atmosphere. Y1.98Eu0.02O3 micro rods were irradiated using a 60Co source with doses from 1 to 100 kGy, and EPR spectra were measured at room temperature in X-band microwave frequencies. Sintered samples exhibited linearity of the main EPR signal response from 10 Gy to 10 kGy. Supralinearity was observed for higher doses, which is possibly ascribed to formation of more defects. Using europium as a dopant enhanced the EPR signal of yttrium rods remarkably, due to 4f–4f transitions of the Eu3+ ion. These innovative findings make europium-doped yttrium oxide a promising material for radiation dosimetry.