NATALIA FIORINI DA SILVA
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Artigo IPEN-doc 26788 Garfield++ simulation of a TH-GEM based detector for standard mammography beam dosimetry2019 - SILVA, N.F.; SILVA, T.F.; CASTRO, M.C.; LUZ, H.N. da; CALDAS, LINDA V.E.The TH-GEM based detector is a robust, simple to manufacture, high-gain gaseous electron multiplier. Its operation is based on a standard printed circuit board (PCB) coated on both sides by metallic material, perforated in a millimeter pattern, and immersed in gas. In order to study the feasibility of using TH-GEM type detectors in dosimetric applications for standard mammography beams, a prototype with adequate dimensions and materials was produced. The present work encompasses the calculations of electric fields by the Gmsh and Elmer software packages and the avalanche simulation using Garfield++ library of a TH-GEM detector filled with Ar/CO2 (70:30) mixture at atmospheric pressure.Artigo IPEN-doc 26539 Dosimetric tests of an extrapolation chamber in standard computed tomography beams2019 - CASTRO, MAYSA C. de; SILVA, NATALIA F. da; CALDAS, LINDA V. E.Computed tomography (CT) diagnostic exams are responsible for the highest dose values to the patients. Therefore, the radiation doses in this procedure must be accurate. For the dosimetry of CT beams, the radiation detector is usually a pencil-type ionization chamber. This type of dosimeter presents a uniform response to the incident radiation beam from all angles, which makes it suitable for such equipment since the X-ray tube executes a circular movement around the table during irradiation. However, there is no primary standard system for this kind of radiation beam yet. In order to search for a CT primary standard, an extrapolation chamber built at the Calibration Laboratory (LCI) of the Instituto de Pesquisas Energéticas e Nucleares (IPEN) was tested. An extrapolation chamber is a parallel-plate ionization chamber that allows the variation of its sensitive air volume. This chamber was used previously for low-energy radiation beams and showed results within the international recommended limits. The aim of this work is to perform some characterization tests (saturation curve, polarity effect, ion collection efficiency and linearity of response) considering the chamber depth of 1.25 mm in the radiation qualities for computed tomography beams at the LCI. The results showed to be within the international recommended limits.Artigo IPEN-doc 26205 Electrical characterization of the amplification plate of a thick-GEM detector for low energy X radiation dosimetry2019 - SILVA, NATALIA F. da; SILVA, TIAGO F.; S. FILHO, LUCAS A.; CASTRO, MAYSA C. de; LUZ, HUGO N. da; CALDAS, LINDA V. E.To evaluate the possible use of Thick-GEM detectors as dosimeters in standard mammography radiation qualities, a prototype is under development for tests. This is a collaboration project between the IPEN Calibration Laboratory and the High Energy Physics and Instrumentation Center (HEPIC-IFUSP). The prototype design takes into consideration many parameters that were obtained in an exploratory work using the Monte Carlo simulation code MCNP5. Using simulations, parameters such as typical dimensions and materials were optimized to match the characteristics of the detector to the requirements of a dosimeter for this purpose. At the present status of the project, electrical tests were undertaken to evaluate the quality of the amplification plate produced in-house. The amplification plate is composed of fiberglass with a thickness of 0.5 mm and 0.03 mm of copper on each side. The average diameter of the orifices in the plate is 0.25 mm, and the distance between centers is 1.00 mm. During the electrical tests, the amplification plate was in a gas chamber filled with Argon at atmospheric pressure. The leakage current was measured as a function of the applied voltage between the copper cladding of both sides. The electrical resistance of 15.3GΩ was obtained. Additionally, the breakdown voltage was observed at approximately 1.0 kV, limiting the maximum amplification voltages to this value.Artigo IPEN-doc 24443 Construção dos componentes de um detector do tipo TH-GEM para metrologia das radiações ionizantes de baixa energia2017 - SILVA, N.F.; SILVA, T.F.; CASTRO, M.C.; LUZ, H.N. da; CALDAS, L.V.E.O detector do tipo Gas Electron Multiplier (GEM) foi proposto inicialmente como um detector sensível à posição, visando à determinação de trajetórias de partículas provenientes de colisões de altas energias. Com o objetivo de estudar o potencial dos detectores do tipo TH-GEM em aplicações dosimétricas para raios-x de baixas energias, especificamente para as qualidades padronizadas de mamografia, foi proposta a construção de um protótipo com características adequadas para tal uso. Neste trabalho foram definidos os parâmetros gerais, estruturais e de materiais aplicáveis às condições desejadas, estabelecendo o processo de construção dos componentes de um protótipo.Artigo IPEN-doc 24141 Performance of an extrapolation chamber in computed tomography standard beams2017 - CASTRO, MAYSA C.; SILVA, NATALIA F.; CALDAS, LINDA V.E.Among the medical uses of ionizing radiations, the computed tomography (CT) diagnostic exams are responsible for the highest dose values to the patients. The dosimetry procedure in CT scanner beams makes use of pencil ionization chambers with sensitive volume lengths of 10 cm. The aim of its calibration is to compare the values that are obtained with the instrument to be calibrated and a standard reference system. However, there is no primary standard system for this kind of radiation beam. Therefore, an extrapolation ionization chamber built at the Calibration Laboratory (LCI), was used to establish a CT primary standard. The objective of this work was to perform some characterization tests (short- and medium-term stabilities, saturation curve, polarity effect and ion collection efficiency) in the standard X-rays beams established for computed tomography at the LCI.Artigo IPEN-doc 24056 Evaluation of the influence of the TH-GEM detector components in dosimetric measurements of standard mammography beams2017 - SILVA, NATALIA F.; SILVA, TIAGO F.; CASTRO, MAYSA C.; CINTRA, FELIPE B.; LUZ, HUGO N. da; CALDAS, LINDA V.E.GEM detectors have found applications in many areas due to their simplicity of construction, low cost, ruggedness and diversity of shape. A dosimeter with these qualities presents utility in several applications, as for example in diagnostic and therapeutic medicine, industrial radiography and nuclear meters. Furthermore, the high sensitivity provided by GEM detectors may extend their applications in low dose dosimetry. Based on these facts, it may be interesting to produce a prototype of a portable TH-GEM type detector with characteristics suitable for dosimetric use in X-rays with low and medium energies. The precise determination of the dosimeter characteristics is very important for laboratories of instrument calibration, as well as to determine how the various components of the detector may influence on the energy deposited in the sensitive volume. In this work, the results obtained about the influence of each one of the components present in this type of detector in standard mammography beams is presented. The code MCNP5 was used. The results allowed the adaptation of the detector to the desired conditions.Artigo IPEN-doc 22873 Comparação entre duas câmaras de ionização do tipo lápis com comprimento de volume sensível de 30 cm2016 - CASTRO, MAYSA C. de; XAVIER, MARCOS; SILVA, NATALIA F.; CALDAS, LINDA V.E.A tomografia computadorizada (CT) vem crescendo devido aos avanços da tecnologia dos equipamentos, proporcionando uma dose maior no paciente, em relação aos demais exames de radiodiagnóstico, levando a uma preocupação com os pacientes. A dosimetria em CT é realizada com uma câmara de ionização do tipo lápis com comprimento de volume sensível de 10 cm. Os estudos têm mostrado a subestimação dos valores de dose. Foram desenvolvidas neste trabalho duas câmaras de ionização com comprimentos de volume sensível de 30 cm, que foram submetidas aos testes principais de caracterização, obtendo-se resultados dentro dos limites recomendáveis internacionalmente.Artigo IPEN-doc 22684 Determinação do fator de correção para atenuação no ar para uma câmara de ionização de ar livre2016 - SILVA, NATALIA F.; CINTRA, FELIPE B.; CASTRO, MAYSA C. de; CALDAS, LINDA V.E.Este trabalho tem como objetivo apresentar os resultados obtidos experimentalmente e por simulação para o fator de correção da atenuação no ar de uma câmara de ionização de ar livre de cilindros concêntricos Victoreen, modelo 481- 5. Este fator de correção foi obtido para as qualidades padronizadas de mamografia, estabelecidas no Laboratório de Calibração de Instrumentos (LCI) do IPEN. Os valores obtidos foram comparados com os resultados do laboratório padrão primário alemão Physikalisch-Technische Bundesanstalt (PTB), obtendo-se diferenças máximas de 0,40% para o valor experimental e de 0,31% para o valor simulado.Artigo IPEN-doc 21410 Caracterização de uma camara de ionização de ar livre para baixas energias2015 - SILVA, NATALIA F.; XAVIER, MARCOS; VIVOLO, VITOR; CALDAS, LINDA V.E.Artigo IPEN-doc 21053 Stability results of a free air ionization chamber in standard mammography beams2015 - SILVA, NATALIA F.; XAVIER, MARCOS; VIVOLO, VITOR; CALDAS, LINDA V.E.