EDUARDO DE LIMA CORREA

EDUARDO DE LIMA CORREA

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High-saturation magnetization in small nanoparticles of Fe3O4 coated with natural oils
2020 - CORRÊA, BRUNO S.; COSTA, MESSIAS S.; CABRERA-PASCA, GABRIEL A.; SENA, CLEIDILANE; PINTO, RAFAEL H.H.; SILVA, ANA P.S.; CARVALHO JUNIOR, RAUL N.; ISHIDA, LINA; RAMON, JONATHAN G.A.; FREITAS, RAFAEL S.; SAIKI, MITIKO; MATOS, IZABELA T.; CORRÊA, EDUARDO L.; CARBONARI, ARTUR W.
The enhancement of nanoparticle’s magnetic properties with a suitable coating is the main tool to increase their potential as an effective candidate for applications in different areas, especially in biomedicine. In the work here reported, Fe3O4 nanoparticles coated with natural oils were synthesized by iron (III) acetylacetonate thermal decomposition and the effects of the coating on the magnetic properties of these particles have been investigated. The oils were extracted from three Amazon fruits seeds: açaí, ucuúba, and bacaba by CO2 supercritical extraction process, and the relative percentage composition of fatty acids were determined by gas chromatography. A systematic study of crystalline, morphological, and magnetic properties revealed a saturation magnetization (Ms) enhancement and high values of the anisotropy constant for Fe3O4 samples when coated with açaí and ucuúba oils, which present a large percentage of saturated total fatty acid. Our results indicate that nanoparticles with sizes smaller than around 5 nm present Ms values as high as that found for bulk Fe3O4 and, consequently, much higher than Ms values for nanoparticles usually coated with oleic acid. The nuclear techniques neutron activation analysis and perturbed angular correlations were used to better characterize the nanoparticles.
Effects of an external magnetic field on the hyperfine parameters in RE2O3 (RE = Gd, Er) nanoparticles measured by perturbed angular correlation spectroscopy
2020 - CORREA, E.L.; BOSCH-SANTOS, B.; SAXENA, R.N.; CABRERA-PASCA, G.A.; CARBONARI, A.W.
In order to understand the interaction mechanisms in RE2O3 (RE=Gd, Er) nanoparticles (NPs), Perturbed Angular Correlation (PAC) spectroscopy, a local technique, plus external magnetic field, was used to elucidate local interactions and possible mapping of the different contribution in these compounds. NPs were synthesized by thermal decomposition and characterized by transmission electron microscopy and X-ray diffraction. PAC measurements were performed using 111In(111Cd) as probe nuclei, with and without the application of an external magnetic field (EMF) of 0.5 T in different temperatures (50 K, 100 K, 200 K, 300 K). Results show that the hyperfine magnetic field is almost zero when the probe is located at the symmetric site, and ∼4 T and ∼5 T for Gd2O3 and Er2O3, respectively, when the probe occupies the asymmetric field.
Effect of the magnetic impurity on the charge diffusion in highly dilute Ce doped LaMnO3
2020 - CABRERA-PASCA, G.A.; BOSCH-SANTOS, B.; BURIMOVA, A.; CORREA, E.L.; CARBONARI, A.W.
LaMnO3+δ is a complex oxide, which, depending on the oxygen excess concentration, presents different crystalline structure and interesting magnetic and electric properties such as colossal magnetoresistance, polaron dynamics, multiferroic behavior, and charge-orbital ordering. This complexity requires different characterization techniques to draw a picture as complete as possible allowing a good understanding of these phenomena. Here, we have used the perturbed angular correlation (PAC) technique to measure hyperfine interactions at La and Mn sites of LaMnO3+δ(δ ∼0.15) using 140Ce and 111Cd at La sites as probe nuclei in order to investigate within an atomic scale the magnetic and electric interactions in this compound. The results show that 111Cd nuclei occupy highly symmetric local sites in agreement with a rhombohedral structure. The magnetic hyperfine field (Bhf ) measured with 111Cd at La sites is very small (Bhf = 0.40 T) due to the supertransferred magnetic field from Mn neighbors through oxygen orbitals. On the other hand, 140Ce nuclei at La sites present a saturation field of around 3.7 T much higher than that expected for La sites (due to the weak transfer field by superexchange mechanism). In addition, for temperature range above the magnetic ordering (200-300 K) a dynamic hyperfine interaction was observed characterized by the attenuation parameter λ(T) whose temperature dependence allowed to determine the activation energy (Ea) associated to charge transfer. The polarization of the 4f -electron of Ce impurities affects the local magnetic field at impurity sites as well as the Ea.
Application of a Tandem system for HVL evaluation in computed tomography
2019 - FONTES, LADYJANE P.; CORREA, EDUARDO L.; POTIENS, MARIA da P.A.
Computed tomography (CT) is a method of imaging used for the diagnosis and treatment of diseases. Different from the conventional diagnostic radiology equipment, where the test for the determination of the half value layer (HVL) is recommended, in CT equipment due to its geometry, the determination of the HVL is a difficult task and is usually only provided by the manufacturer. The effective energy of a beam is determined by definition, by means of HVL determination. When HVL values are not easily determined, as in the case of CT, it is possible to evaluate the effective energy of the beam through a system consisting of the use of different energy dependent dosimeters, where the ratio between the calibration curve responses in energy can provide the effective energy of the beam (Tandem system). The system used in this work for the evaluation of HVL in computed tomography is composed of groups formed by an ionization chamber of the pencil-type and cylindrical absorber layers of aluminum and Polymethyl methacrylate (PMMA).
Influence of the vials radioactive residue in Nuclear Medicine procedure applied to a new “in situ” activimeter calibration methodology
2019 - KUAHARA, L.T.; CORREA, E.L.; CARNEIRO, R.C.G.; BEZERRA, R.R.L.; POTIENS, M.P.A.
In this study we present a new “in situ” calibration methodology establishment for activimeters – i.e., this equipment calibration can be made at the hospital and/or the nuclear medicine service (NMS) – and also the importance of considering vials radioactive residue when generating the calibration coefficient in terms of activity (NA). For the calibration, two methods are presented here: in the first, 99mTc sample activity (AC) is measured in the NMS. Then it is sent to the Instruments Calibration Laboratory (LCI/IPEN) where the reference activity (AR) is obtained under controlled conditions in a reference vial. After geometry and residue corrections, NA is calculated. In the second method, AR is obtained at the LCI, then 99mTc sample is sent to the hospital/NMS, where AC is measured and NA calculated. Calibration methodologies were applied to three NMS and to four equipment belonging to the radiopharmaceutical production facility (CR) at the Nuclear and Energy Research Institute (IPEN). Both methodologies were tested with and without residual activity corrections under controlled conditions. Variations of up to 4% were obtained.
Properties of Gdsub(2)Osub(3) nanoparticles studied by hyperfine interactions and magnetization mesurements
2016 - CORREA, E. L.; BOSCH SANTOS, B.; CAVALCANTE, F.H.M.; CORREA, B.S.; FREITAS, R.S.; CARBONARI, A.W.; POTIENS, M.P.A.