ROBINSON ALVES DOS SANTOS

ROBINSON ALVES DOS SANTOS

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A comparative study on the performance of radiation detectors from the HgI2 crystals grown by different techniques
2011 - MARTINS, J.F.T.; COSTA, F.E.; SANTOS, R.A.; MESQUITA, C.H.; HAMADA, M.M.
There have been attempts to develop room-temperature X- and gamma ray semiconductor detectors for various applications. The main physical semiconductor properties required for fabrication of room temperature semiconductor detectors are: (1) high atomic number; (2) high density; (3) high absorption coefficient; (4) a band gap large enough to keep leakage currents low, at room temperature and (5) large electron and hole mobility-lifetime products, for an efficient charge collection [1, 2]. Among these types of detectors, HgI2 has emerged as a particularly interesting material in view of its wide band gap (2.13 eV) and its large density (7.5 g/cm3 ). HgI2 crystals are composed of high atomic number elements (ZHg=80 and Zi=53) and with high resistivity (>1014 ficm). These are important factors in applications where compact and small thickness detectors are necessary for X- and gamma rays measurements. However, the applications of Hgi2 are limited by the difficulty in obtaining high-quality single crystals and the long-term reliability problems in devices made from crystals [1]. in this work, the Hgi2 crystals were grown using four different techniques: (a) physical vapor transport, (b) solution from dimethyl sulfoxide complexes, (c) vapor growth of HgI2 precipitated from acetone and (d) Bridgman method. The obtained crystals for four methods were characterized considering the following physical chemistry properties: crystal stoichiometry, crystal structure, plan of the crystal orientation, surface morphology of the crystal and crystal impurity. The influence of these physical chemistry properties on the crystals developed by four techniques was studied, evaluating their performance as a radiation detector. The best result of radiation response was found for the crystal grown by physical vapor transport. Also, the dependence of the radiation response on the HgI2 crystal purity was also studied. For this, the HgI2 raw material was purified by the many pass zone refining technique. A significant improvement in the characteristics of the detector-crystal was achieved, when the starting materials became purer.
Multiferroic bismuth ferrite
2020 - MARSCHICK, G.; SCHELL, J.; STÖGER, B.; GONÇALVES, J.N.; KARABASOV, M.O.; ZYABKIN, D.; WELKER, A.; ESCOBAR C., M.; GÄRTNER, D.; EFE, I.; SANTOS, R.A.; LAULAINEN, J.E.M.; LUPASCU, D.C.
Work of numerous research groups has shown different outcomes of studies of the transition from the ferroelectric α-phase to the high temperature β-phase of the multiferroic, magnetoelectric perovskite Bismuth Ferrite (BiFeO3 or BFO). Using the perturbed angular correlation (PAC) method with 111mCd as the probe nucleus, the α to β phase transition was characterized. The phase transition temperature, the change of the crystal structure, and its parameters were supervised with measurements at different temperatures using a six detector PAC setup to observe the γ -γ decay of the 111mCd probe nucleus. The temperature dependence of the hyperfine parameters shows a change in coordination of the probe ion, which substitutes for the bismuth site, forecasting the phase transition to β-BFO by either increasing disorder or formation of a polytype transition structure. A visible drop of the quadrupole frequency ω0 at a temperature of about Tc ≈ 820◦ C indicates the α-β phase transition. For a given crystal symmetry, the DFT-calculations yield a specific local symmetry and electric field gradient value of the probe ion. The Pbnm (β-BFO) crystal symmetry yields calculated local electric field gradients, which very well match our experimental results. The assumption of other crystal symmetries results in significantly different computed local environments not corresponding to the experiment.
Hyperfine interactions measurements in bismuth tri-iodide (BiI3) by time differential perturbed angular correlation spectroscopy (TDPAC)
2019 - SANTOS, R.A.; SANTOS, B.B.; CORREA, E.L.; PEREIRA, L.F.D.; SCHELL, J.; CORREIA, J.G.M.; LUPASCU, D.C.; SCHAAF, P.; HOFSAESS, H.C.; SAXENA, R.N.; CARBONARI, A.W.
Bismuth tri-iodide (BiI3) is a material of great interest in applications such as solar cells and semiconductor detectors. In the work reported here, bulk samples of BiI3 were characterized by time differential perturbed angular correlation spectroscopy (TDPAC) at different temperatures using 111mCd (111Cd) and 111In (111Cd) as radioactive probes, inserted by implantation at ISOLDE/CERN and by thermal diffusion at IPEN, respectively. TDPAC measurements were used to investigate the hyperfine interactions at Bi sites in the crystalline structure of BiI3. The hyperfine parameters obtained were analyzed to elucidate the electrical properties expected for the mentioned technological applications. The optimal temperatures for annealing after the implantation (300°C and 320°C) were determined, allowing to observe the perturbation pattern R(t). Measurements show that the incidence of UV light at 350–363nm wavelength has an effect on the electronic structure around the Cd probe nuclei located near the surface of samples.
Study of the local magnetics and electrics properties at Gd2Ti2O7 by PAC spectroscopy and ab initio calculations
2019 - CORREA, E.L.; PEREIRA, L.F.; FERREIRA, W.L.; BOSCH-SANTOS, B.; SCALISE, L.; GONÇALVES, V.; SANTOS, R. dos; SCHELL, J.; CARBONARI, A.W.
Gd2Ti2O7 exhibits a complex magnetic behavior with a geometrically frustrated antiferromagnetic ordering below TN = 1.1 K and a second magnetic transition at 0.7 K. In the work here reported, perturbed angular correlation (PAC) technique was used in order to measure electric quadrupole hyperfine interactions at 111mCd probe nuclei on Ti sites. These experimental results along with those for magnetic hyperfine interactions at 155Gd previously reported from Mossbauer Effect spectroscopy were interpreted with electronic structure first-principles calculation. Single and doped-Cd cell simulations have been performed with potential linearized augmented plane waves methods and generalized gradient approximation from Perdew-Burke-Ernzerhorf embodied within the WIEN2k all-electron code. PAC measurements have exhibited 111mCd probes occupying two fraction sites characterized by well-defined quadrupole frequencies (as shown in the spin-rotation spectra in the figure) with almost the same values for the corresponding electric field gradient (efg), however, with slightly difference in the asymmetry parameters. Theoretical efg’s obtained for Cadmium atoms located at Gd or Ti sites of the pyrochlore structure indicate that both experimental hyperfine parameters corresponding to Cd at Titanium site.
Optimization of the HgI2 Crystal preparation for application as a radiation semiconductor detector
2018 - MARTINS, JOAO F.T.; SANTOS, ROBINSON A. dos; FERRAZ, CAUE de M.; OLIVEIRA, RENE R.; FIEDERLE, MICHAEL; AMADEU, RAFAEL de A.; SANTOS, RODRIGO S. dos; SILVA, THIAGO L.B. da; HAMADA, MARGARIDA M.
The effect of HgI2 crystal encapsulation using different polymer resins, with the intent of avoiding the oxidation of the crystal surface, was evaluated in this work. The crystal was purified and grown by the physical vapor transport (PVT) technique modified. Systematic measurements were carried out for evaluating the stoichiometry, structure orientation, surface morphology and impurity of the crystal grown. The purer region of the crystal grown was selected to be prepared as a radiation detector, applying water-based conductive ink contacts and copper wire on the crystal surfaces. After that, the crystal was encapsulated with a polymeric resin which insulates atmospheric gases, aiming to improve the stability of the HgI2 detector. Four resins were used for crystal encapslation and the performance of the detector depended on the composition of the resins used. Among the four resins studied to evaluate the influence of encapsulation on the performance of crystals, as a radiation detector, the best result of resistivity and energy spectrum was obtained for the resin #3 (50% - 100% of Methylacetate and 5% - 10% of n-butylacetate). The encapsulation of crystals with polymer resins, performed with the intent of avoiding the oxidation of the crystal surface, did not compromise the measurements and were fully capable of detecting the presence of gamma radiation. The stability of the encapsulated HgI2 crystal detector was of up to 78 hs, while the stability found for HgI2 detector no encapsulated was in order 3 ~4 hs.
Purification and crystal growth of the bismuth (III) iodide-influence of trace impurities on the crystal quality
2017 - FERRAZ, CAUE de M.; ARMELIN, MARIA J.A.; OLIVEIRA, RENE R.; OTUBO, LARISSA; MARTINS, JOAO F.T.; SANTOS, ROBINSON A. dos; COSTA, FABIO E.; CARVALHO, DIEGO V.S.; OMI, NELSON M.; MESQUITA, C.H.; HAMADA, MARGARIDA M.
This work describes the experimental procedure of purification and preparation of BiI3 crystals by Repeated Vertical Bridgman technique, aiming a future application of this semiconductor crystal as a room temperature radiation detector. The BiI3 powder used as raw material was purified three times and, at each purification, the crystal was evaluated by systematic measurements of the reduction of the impurities, crystalline structure, stoichiometry and surface morphology. The reduction of the trace metal impurities in the BiI3, at each purification, was analyzed by Instrumental Neutron Activation Analysis (INAA), in order to evaluate the efficiency of the purification technique established in this work. It was demonstrated that the Repeated Bridgman technique is effective to reduce the concentration of many impurities in BiI3, such as Ag, As, Br, Cr, K, Mo, Na and Sb. The crystalline structure of the BiI3 crystal purified twice and three times was similar to BiI3 pattern. However, for BiI3 powder and purified once, an intensity contribution of the BiOI was observed in the diffractograms. Improvement in the stoichiometric ratio was observed at each purification step, as well as the crystal surface morphology.
Experimental and MCNP studies of paraffin and polyethylene in neutron moderation and BF3 detector efficiency
2013 - CARDENAS, JOSE P.N.; MADI FILHO, TUFIC; PETRI, ANNA R.; SANTOS, ROBINSON A. dos; MARTINS, JOAO F.T.; CARVALHO, DIEGO V.S.; ALVARENGA, T.; BELLEZZO, M.; LARANJO, G.; LIMA, M.; OLIVEIRA, P.; PEREIRA, MARIA da C.C.
The Nuclear and Energy Research Institute – IPEN, offers post-graduate programs, namely: Nuclear Technology - Applications (TNA), Nuclear Technology - Materials (TNM), Nuclear Technology - Reactors (TNR). The Institute programs mission is to form expert technicians and engineers with a strong knowledge in their discipline to work in the nuclear area. The course: “Theoretical Fundaments and Practices of the Instrumentation used in Nuclear Data Acquisition” covers the use of laboratory nuclear instrumentation and the accomplishment of experiments to obtain nuclear parameters. One of these experiments is object of this work: “Experimental and MCNP Studies of Paraffin and Polyethylene Neutron Moderation and BF3 Detector Efficiency”. Neutrons are uncharged particles and, therefore, cannot be detected by Coulomb interactions. Thus, the detector assembly used must contain some kind of material with high cross section for interaction with neutrons, called converters. A boron trifluoride (BF3) detector was used in this experiment to detect neutron in real time. However, the response of this arrangement varies according to the energy range of incident neutrons. Their efficiency for thermal neutrons is above 90%, but, this result decreases, significantly, for neutrons of energy greater than 0.5 eV. The neutron moderation and, consequently, its energy variation were obtained by interposing different thicknesses of moderator material (Paraffin or Polyethylene) between the source and the detector.
Am-Be neutron irradiator used for nuclear instrumentation training
2013 - MADI FILHO, TUFIC; CARDENAS, JOSE P.N.; PETRI, ANNA R.; SANTOS, ROBINSON A. dos; MARTINS, JOAO F.T.; CARVALHO, DIEGO V.S.; ALVARENGA, T.; BELLEZZO, M.; LARANJO, G.; LIMA, M.; OLIVEIRA, P.; PEREIRA, MARIA da C.C.
A neutron irradiator was assembled at IPEN (Nuclear and Energy Research Institute) facility to perform qualitative-quantitative analysis of materials, using thermal and fast neutrons. In order to determine the 116mIn decay constant, a thermal flux obtained experimentally by Monte Carlo N-Particle Transport Code-MCNP, in a previous work, was used in the nuclear experiment. The activity calculated from the activation parameters was 13.51±0.17 kBq and the activity determined experimentally was 12.51± 0.36 kBq. The decay constant determined by the pulse height analyzer (PHA) measures was 211.4 μ·s-1, and that determined by fitting the data using a Multichannel Scaler (MCS) system was 200.3 ± 1.6 μ·s-1. The half-life of 116mIn found in the literature is 3256.8 s, which corresponds to a decay constant of 212.8 μ·s-1. The present experiment does not intend to establish a new value for the decay constant: it solely aims students’ practical exercises in nuclear properties of elements. This experiment is part of the nuclear experimental course.
Influence of impurities on the radiation response of the TlBr semiconductor crystal
2017 - SANTOS, ROBINSON A. dos; MESQUITA, CARLOS H. de; SILVA, JULIO B.R. da; FERRAZ, CAUE de M.; COSTA, FABIO E. da; MARTINS, JOAO F.T.; GENNARI, ROSELI F.; HAMADA, MARGARIDA M.
Two commercially available TlBr salts were used as the rawmaterial for crystal growths to be used as radiation detectors. Previously, TlBr salts were purified once, twice, and three times by the repeated Bridgmanmethod. Thepurification efficiency was evaluated by inductively coupled plasma mass spectroscopy (ICP-MS), after each purification process. A compartmental model was proposed to fit the impurity concentration as a function of the repetition number of the Bridgman growths, as well as determine the segregation coefficients of impurities in the crystals. The crystalline structure, the stoichiometry, and the surface morphology of the crystals were evaluated, systematically, for the crystals grown with different purification numbers. To evaluate the crystal as a radiation semiconductor detector, measurements of its resistivity and gamma-ray spectroscopy were carried out, using 241Am and 133Ba sources. A significant improvement of the radiation response was observed in function of the crystal purity.
Estudo da influência de impurezas e da qualidade das superfícies em cristais de brometo de tálio para aplicação como um detector de radiação
2016 - SANTOS, ROBINSON A. dos
Neste trabalho, cristais de TlBr foram crescidos e purificados pelo método de Bridgman Repetido, a partir de sais comerciais de TlBr, e caracterizados para serem usados como detectores de radiação à temperatura ambiente. Para avaliar a eficiência de purificação, estudos da diminuição da concentração de impurezas foram feitos após cada crescimento, analisando as impurezas traço por Espectrometria de Massas com Plasma (ICP-MS). Um decréscimo significativo da concentração de impurezas em função do número de purificações foi observado. Os cristais crescidos apresentaram boa qualidade cristalina de acordo com os resultados de análise por Difração de Raios X (DRX), boa qualidade morfológica e estequiometria adequada de acordo com os resultados de análise por MEV(SE) e MEV(EDS). Um modelo matemático definido por equações diferenciais foi desenvolvido para avaliar as concentrações de impurezas no cristal de TlBr e suas segregações em função do número de crescimentos pelo método de Bridgman. Este modelo pode ser usado para calcular o coeficiente de migração das impurezas e mostrou ser útil para prever o número necessário de repetições de crescimento Bridgman para atingir nível de pureza adequado para assegurar a qualidade do cristal como detector de radiação. Os coeficientes se segregação obtidos são parâmetros importantes para análise microestrutural e análise de transporte de cargas nos cristais detectores. Para avaliar os cristais a serem usados como detectores de radiação, medidas de suas resistividades e resposta à incidência de radiação gama das fontes de 241Am (59,5keV) e 133Ba (81 keV) foram realizadas. Essa resposta foi dependente da pureza do cristal. Os detectores apresentaram um avanço significativo na eficiência de coleta de cargas em função da pureza.