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Artigo IPEN-doc 31172 Influence of LiF on the Sintering of Si3N4 Ceramics Containing SiO2–CaO–Al2O3
2025 - CORREA, W.T.; SILVA, R.O.; FERREIRA, T.S.; CARVALHO, F.M.S.; GUEDES-SILVA, C.C.
This study investigates the influence of LiF on the sintering behavior of Si3N4 ceramics with SiO2–CaO–Al2O3 at the eutectic composition. Compositions containing 90 wt.% Si3N4 were sintered at 1650–1815 °C for 1 hour. The ceramics were characterized in terms of density, microstructure, and hardness. At 1650 °C, the β/(α+β)-Si3N4 ratio rose from 28.4 % (0 wt.% LiF) to 63.7% (2 wt.% LiF), exceeded 98 % at 1700 °C, and reached 100 % at ≥ 1770 °C. In LiF-free samples, higher sintering temperatures resulted in a higher relative density (95.6 ± 0.4%) and hardness (12.99 ± 0.42 GPa). LiF improved densification and hardness at low content and sintering temperature, yielding 89.4 ± 0.3 % relative density and 9.71± 0.42 GPa hardness (1 wt.% LiF) compared to 84.1 ± 0.5 % and 6.78 ± 0.29 GPa (0 wt.% LiF), both at 1650 °C. At higher temperatures, LiF decreased both properties, likely due to its tendency to evaporate.
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Artigo IPEN-doc 31171 Enhancing jawless VMAT plan quality for hypofractionated left breast cancer with the avoidance structure tool
2025 - CASTELO, J.H.M.; MENEZES, D.C.T.; BITTENCOURT, G.R.; ROSA, L.A.R. da; BONIFACIO, D.A.B.
Introduction: The Avoidance Structure (AvS) tool shields a structure by maintaining the multileaf collimator leaves over the structure's projection in the beam's eye view. In this work, we tested the dosimetric impact of using part of the outlines of the heart and lungs as avoidance structure when creating knowledge-based left breast volumetric modulated arc therapy treatment plans. Methods: Dose-volume histogram estimates were calculated using a RapidPlan model for 30 patients who received whole breast radiation therapy in five fractions. Then, two sets of plans were generated for a Halcyon v2 linear accelerator by alternating the use of the AvS tool. Dose metrics for both procedures were compared. Results: Coverage on the target volume remained similar regardless of the use of AvS. The mean absorbed dose received by the heart, as well as the relative volumes receiving 1.5, 3.5 and 7.8 Gy, decreased with effect sizes (ESZ) 0.98, 1.43, and 0.63 respectively. Homolateral lung volumes receiving 1.5 and 3.5 Gy were also lowered using AvS. However, the dose received by 0.03 cc of the contralateral breast increased with an ESZ of 0.52. Conclusions: Except for the contralateral breast, the AvS tool improved DVH metrics for organs at risk without compromising target coverage or worsening hotspots.
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Artigo IPEN-doc 31169 Insights and simulation of metascintillator-based brain PET systems to enhance ToF capability
2024 - BONIFACIO, D.A.B.; LATELLA, R.; MURATA, H.M.; BENLLOCH, J.M.; GONZALEZ, A.J.; LECOQ, P.; KONSTANTINOU, G.
The integration of Time-of-Flight (ToF) information into Positron Emission Tomography (PET) image reconstruction enhances both signal-to-noise ratio and the localization of annihilation events. A critical component contributing to the accuracy of ToF-PET is the scintillator. To overcome the time resolution limitations in conventional scintillators, the metascintillator approach has been proposed. The metascintillator is an engineered composition of small units that combines and optimizes various features within a single scintillator heterostructure. In this work, metascintillator-based brain PET systems were simulated using the GATE toolkit and compared with designs based on bulk LYSO or BGO. Sensitivity, noise equivalent count rate (NECR) and scatter fraction were evaluated following NEMA guidelines. To match the peak sensitivity of a system utilizing a 15 mm bulk BGO, the metascintillator-based scanners using BGO/BaF2, BGO/EJ232, LYSO/BaF2 and LYSO/EJ232 must possess thicknesses of 23.2 mm, 22.5 mm, 29.7 mm and 31.1 mm, respectively. With ToF gain, the scanner utilizing a 25 mm thick LYSO-EJ232 metascintillator exhibited the most promising NECR curve, peaking at 1180 cps at 1600 MBq. This work takes a significant step towards harnessing the information gain facilitated by the integration of metascintillator-based detectors in PET imaging.
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Artigo IPEN-doc 31120 High red luminescence intensity under sunlight exposure of a PMMA polymer doped with a tetrakis Eu3+ b-diketonate complex containing a benzimidazolium counterion
2025 - ASSUNÇAO, ISRAEL P.; COSTA, ISRAEL F.; BLOIS, LUCCA; FELINTO, MARIA C.F.C.; DEFLON, VICTOR M.; ANDO, ROMULO A.; MALTA, OSCAR L.; BRITO, HERMI F.
New tetrakis Eu3+ and Gd3+ b-diketonate complexes containing benzimidazolium (Bzim) as the counterion were synthesized by the one-pot method. The Bzim[Eu(tta)4]$H2O complex was further incorporated into a poly(methyl methacrylate) matrix (PMMA) at 1, 5, and 10% (w/w), which revealed highly desirable photonic features. The Eu3+ and Gd3+ complexes were characterized by elemental and thermal analyses, in addition to ESI-MS spectrometry, FTIR, and Raman spectroscopy. Single-crystal X-ray diffraction studies of the tetrakis Bzim[Eu(tta)4]$EtOH complex revealed that the Bzim+ counteraction and EtOH molecules exhibited several intermolecular interactions with very short hydrogen bond distances between two [Eu(tta)4]− anion units. The PMMA:(1%) Bzim[Eu(tta)4]-doped material was thermally stable up to 120 °C, which was close to the values found for the Eu3+-complex. Regarding the photoluminescence properties, either the Bzim[Eu(tta)4]$H2O or the doped films showed intense emission arising from the metal ion over a wide range of excitation wavelengths comprising UVA, UVB, and UVC regions. In addition, when the polymer films were exposed to sunlight radiation in an open external environment, the materials revealed a high Eu3+-centered red emission arising from the 5D0 / 7FJ transition. The Bzim[Eu(tta)4]$H2O and Bzim[Eu(tta)4]$EtOH complexes showed high absolute quantum yields (QL Eu) of 56% and 70%, respectively, whereas the doped polymer films displayed only ∼38%. All materials exhibited a highly red monochromatic emission characteristic. We believe that such luminescent systems could be promising photonic materials with a wide excitation range, including UVA, UVB, UVC, and sunlight, acting as efficient light-converting molecular devices (LCMDs).