MARGARIDA MIZUE HAMADA

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Agora exibindo 1 - 10 de 201
  • Artigo IPEN-doc 29128
    Zonal refining and Bridgman technique for CsI:Tl scintillation crystal growth
    2022 - SUZART, K.F.; PEREIRA, M.C.C.; HAMADA, M.M.; MESQUITA, C.H.
    This work describes the development of the crystal cesium iodide doped with thallium (CsI:Tl) for use as a radiation detector. For CsI salt purification the zonal refining methodology using a horizontal oven at a constant temperature of 700 °C was used. The high temperature region corresponds to approximately 10% of the salt bed containing (260 mm). This region moves at a speed of 50 mm/h. The crystal growth was carried out by Bridgman technique, using a vertical oven at speed of 1 mm/h.
  • Resumo IPEN-doc 26498
    Biokinetics and radiation dosimetry for [4-(14)C]-cholesterol in humans
    2011 - MARCATO, L.A.; HAMADA, M.M.; MESQUITA, C.H.
    Medical and clinical researches utilize radiolabelled cholesterol to obtain information about the physiology of cholesterol and of its several substrates (biliary acids, hormones and vitamins) in the body. The radiotracers constitute a simple and accurate tool for metabolic studies; however, the scientific community has shown certain reservations concerning the use of radioisotopes. Probably, the apprehension is result of the question about the deleterious radiation effects. Although the studies that utilize radioisotopes are approved by strict ethic committees, most of them do not mention the radiometric doses at which the human subjects are exposed during these studies. The International Commission on Radiological Protection (ICRP) provides a generic carbon model (GCM) to calculate the effective dose of compounds labeled with 14C, first described on ICRP publication 30. The effective dose coefficients for most compounds appear to be greatly overestimated by the GCM in comparison with those generated by more realistic models [1]. The GCM cannot be applied to the interpretation of bioassay data with any degree of confidence [1]. The purpose of the present study is to improve the generic biokinetic model [2] for use in the assessment of the internal dose received by human subjects who were administered labelled cholesterol either orally or intravenously. This model was used with the ANACOMP software to estimate the radiometric doses with the MIRD techniques. To validate the model, the simulated profile curves were compared with the profile curves described on the literature (Kruskal-Wallis test, P=0.4232). The model reproduced the intestinal absorption of cholesterol and the excretion of cholesterol in feces and urine. The estimated effective dose coefficient calculated for the reference man described on ICRP publication 23 was 1.35x10-11 SvBq-1. The organs that received the highest equivalent dose were the lower large intestine (1.03x10-10 GyBq-1), upper large intestine (3.74x10-11 GyBq-1) and small intestine (1.58x10-11GyBq-1). The effective dose coefficient calculated by the proposed dosimetric model was approximately forty-three times lower than that which is calculated by the ICRP generic model (5.8x10-10 SvBq-1) for ingested 14C that assumes complete absorption to blood.
  • Resumo IPEN-doc 15721
    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.
  • Resumo IPEN-doc 15453
    Development of the mechanical system on a third-generation industrial computed tomography scanner in Brazil
    2011 - CALVO, WILSON A.P.; MESQUITA, CARLOS H. de; SPRENGER, FRANCISCO E.; COSTA, FABIO E. da; SALVADOR, PABLO A.V.; CARVALHO, DIEGO V. de S.; HAMADA, MARGARIDA M.
    The development of measurement geometry for medical X-ray computed tomography (CT) scanners carried out from the first to the fourth-generation. This concept has also been applied for imaging of industrial processes such as pipe flows or for improving design, operation, optimization and troubleshooting. Nowadays, gamma CT permits to visualize failure equipment points in three-dimensional analysis and in sections of chemical and petrochemical industries. The aim of this work is the development of the mechanical system on a third-generation industrial CT scanner to analyze laboratory gas absorption column which perform highly efficient separation, turning the 60Co, 137Cs or 192Ir sealed gamma-ray source and the NaI(Tl) multidetector array. It has also a translation movement along the column axis to obtain as many slices of the process flow as needed. The mechanical assembly for this third-generation industrial CT scanner is comprised by strength and rigidity structural frame in stainless and carbon steels, rotating table, source shield and collimator with pneumatic exposure system, spur gear system, translator, rotary stage, drives, and stepper motors. The use of suitable spur gears has given a good repeatability and high accuracy in the degree of veracity. The data acquisition boards, mechanical control interfaces, software for movement control and image reconstruction were specially development. This third-generation industrial CT scanner has obtained good spatial resolution and images. The filtered back projection (FBP) tomographic reconstruction algorithm used has shown a faster convergence. The mechanical system presented a good performance in terms of strength, rigidity, accuracy and repeatability with great potential to be used for education or program dedicated to training chemical and petrochemical industry professionals and for industrial process optimization in Brazil.
  • Resumo IPEN-doc 15341
    Development of a gamma ray computed tomography technique for random packed columns analysis
    2008 - MESQUITA, CARLOS H. de; VASQUEZ, PABLO A.S; PEREIRA, JOAO C.S. de M.; MARTINS, JOAO F.T.; CALVO, WILSON A.P.; HAMADA, MARGARIDA M.
  • Artigo IPEN-doc 28353
    Obtenção e análise de espectros de energia para detectores de radiação com osciloscópio digital e software tipo planilha eletrônica
    2021 - GONCALVES, SILAS A.; CANAZZA, SAMUEL A.; COSTA, FABIO E. da; HAMADA, MARGARIDA M.
    Detectores de radiação que produzem um pulso, cuja amplitude é proporcional a energia da radiação incidente, permitem com auxílio de uma eletrônica apropriada e de um analisador multicanal, a obtenção do espectro de energia da radiação incidente sobre o detector. Devido ao analisador multicanal nem sempre estar disponível em laboratórios, este trabalho propõe uma alternativa de medida do espectro utilizando-se dos recursos disponíveis nos osciloscópios digitais de efetuar a medida da amplitude dos pulsos e enviar a um computador tipo PC. No computador, uma planilha eletrônica adequadamente configurada pode então trabalhar os dados coletados no osciloscópio e obter o espectro de energia. Adicionalmente, um segundo recurso permite a seleção temporal da largura do pulso que minimiza leituras incorretas da amplitude na eventualidade de ocorrer empilhamento de pulsos. Para os experimentos foram utilizados um osciloscópio Tektronix TDS 30302B e a planilha eletrônica Excel®. Os espectros foram comparados com os obtidos com um analisador multicanal e se mostraram iguais ou melhores, mas que tiveram como limitação a baixa taxa de aquisição do osciloscópio que foi da ordem de apenas 2 pulsos/seg, portanto milhares de vezes menor que de um analisador multicanal.
  • Artigo IPEN-doc 28297
    Zonal refining and Bridgman technique for CsI:Tl scintillation crystal growth
    2021 - SUZART, K.F.; PEREIRA, M.C.C.; HAMADA, M.M.; MESQUITA, C.H.
  • Artigo IPEN-doc 28281
    Study of the energy spectrum for radiation detectors with digital oscilloscope and worksheet software
    2021 - GONÇALVES, S.A.; CANAZZA, S.A.; COSTA, F.E.; HAMADA, M.M.
  • Artigo IPEN-doc 28258
    Portable radiation detector with PIN photodiode for x-rays and CsI(Tl) scintilator with photodiode for gamma rays
    2021 - CANAZZA, S.A.; GONÇALVES, S.A.; COSTA, F.E.; HAMADA, M.M.
  • Artigo IPEN-doc 28326
    Desenvolvimento de detector portátil de radiação usando simultaneamente fotodiodo de silício para raios-x e cintilador com fotodiodo para raios gama
    2021 - CANAZZA, SAMUEL A.; GONCALVES, SILAS A.; COSTA, FABIO E. da; HAMADA, MARGARIDA M.
    Neste trabalho foi desenvolvido um detector portátil de radiação usando como meio detector um fotodiodo de silício para raios-X e um cintilador de CsI(Tl) com fotodiodo para radiação gama. A configuração dos detectores foi estudada utilizando fotodiodos em paralelo com um único pré-amplificador e com pré-amplificadores em paralelo, buscando o menor ruído do conjunto e com isso aumentar a faixa de energias detectadas.