ANNA RAQUEL PETRI
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Artigo IPEN-doc 25858 Effect of the ohmic drop in a RPC-like chamber for measurements of electron transport parameters2019 - PETRI, A.R.; MANGIAROTTI, A.; GONCALVES, J.A.C.; BUENO, C.C.The main advantage of Resistive Plate Chambers (RPCs), applied, for instance, in High-Energy Experiments and Positron Emission Tomography (PET), is that it is spark-protected due to the presence of, at least, one high-resistive electrode. However, the ohmic drop across the latter can affect the charge multiplication significantly. In this work, we investigate this effect in a RPC-like chamber. The counter was filled with nitrogen at atmospheric pressure and the primary ionization was produced by the incidence of nitrogen pulsed laser beam on an aluminum cathode. The illumination area of the cathode was measured using a foil of millimetric paper overlaid on this electrode. In this way, the resistance of the glass anode could be estimated using the known resistivity of the glass (ρ=2×1012 Ω.cm). Therefore, the voltage drop across the dielectric was calculated by the product of the current across the gas gap and the anode resistance. In order to mitigate the effect of the resistive electrode, the laser beam intensity was limited by interposing metallic meshes between the laser and the chamber window. The dependence of the ohmic drop from the applied voltage was analyzed. The results obtained shown that, without the meshes, the ohmic drop corresponds up to 7% of the applied voltage, preventing the detection system to reach values of density-normalized electric fields in the gas gap (Eeff/N) higher than 166 Td. By minimizing the laser beam intensity and, consequently, the primary ionization, the ohmic drop represented only 0.2% of the applied voltage, extending the Eeff /N range up to 175 Td.Artigo IPEN-doc 24098 Effect of the ohmic drop in a RPC-like chamber for measurements of electron transport parameters2017 - PETRI, ANNA R.; MANGIAROTTI, ALESSIO; GONÇALVES, JOSEMARY A.C.; BUENO, CARMEN C.The main advantage of Resistive Plate Chambers (RPCs), applied, for instance, in High-Energy Experiments and Positron Emission Tomography (PET), is that it is spark-protected due to the presence of, at least, one highresistive electrode. However, the ohmic drop across the latter can affect the charge multiplication significantly. In this work, we investigate this effect in a RPC-like chamber. The counter was filled with nitrogen at atmospheric pressure and the primary ionization was produced by the incidence of nitrogen pulsed laser beam on an aluminum cathode. The illumination area of the cathode was measured using a foil of millimetric paper overlaid on this electrode. In this way, the resistance of the glass anode could be estimated using the known resistivity of the glass (ρ=2×1012 Ω.cm). Therefore, the voltage drop across the dielectric was calculated by the product of the current across the gas gap and the anode resistance. In order to mitigate the effect of the resistive electrode, the laser beam intensity was limited by interposing metallic meshes between the laser and the chamber window. The dependence of the ohmic drop from the applied voltage was analyzed. The results obtained shown that, without the meshes, the ohmic drop corresponds up to 7% of the applied voltage, preventing the detection system to reach values of density-normalized electric fields in the gas gap (Eeff/N) higher than 166 Td. By minimizing the laser beam intensity and, consequently, the primary ionization, the ohmic drop represented only 0.2% of the applied voltage, extending the Eeff /N range up to 175 Td.Tese IPEN-doc 23096 Medidas do primeiro coeficiente de Townsend de ionização em misturas gasosas utilizadas em microdosimetria2017 - PETRI, ANNA R.Microdosímetros gasosos geralmente empregam uma mistura gasosa equivalente ao tecido humano mole (Tissue-equivalent Gas TEG), composta de um hidrocarboneto, dióxido de carbono e nitrogênio, de forma que o poder de freamento na mistura e no tecido sejam semelhantes. Entretanto, independentemente do hidrocarboneto adotado, dados tanto teóricos como experimentais do primeiro coeficiente de Townsend de ionização (α) nestas misturas são raros, ainda que a primeira TEG, cujo metano é o gás majoritário, tenha sido proposta em 1956 por Rossi e Failla e continue sendo amplamente utilizada. Neste trabalho, dados do parâmetro α em TEGs baseadas no metano (CH4 64,4%, CO2 32,4% e N2 3,2%) e nos isômeros do butano (C4H10 51,4%, CO2 42,3% e N2 6,3%) são apresentados pela primeira vez em geometria planar para a faixa de campo elétrico normalizado pela densidade do gás (E/N) entre 100 290 Td (1 Td = 10-21 V.m2). O método de medidas adotado baseia-se na técnica de Townsend pulsada, onde o primeiro coeficiente de Townsend pode ser determinando comparando a corrente elétrica no regime de avalanche e a corrente de ionização primária gerada pela incidência de um feixe de laser de nitrogênio em um eletrodo metálico (catodo) de uma câmara de geometria planar, sendo o anodo um eletrodo de alta resistividade (ρ=2×1010Ω.m). O aparato experimental, até então operado apenas em pressão atmosférica, foi modificado para também trabalhar em baixa pressão (120 hPa), de modo a aumentar a faixa de E/N investigada. A validação do método e das alterações do sistema de detecção foi realizada utilizando os três gases componentes das TEGs cujos parâmetros de transporte são amplamente estudados: o nitrogênio, o dióxido de carbono e o metano. Observou-se que o parâmetro na TEG com metano assemelha-se com os valores determinados para o metano puro. Na TEG baseada no isobutano, ele é compatível com o primeiro coeficiente de Townsend do dióxido de carbono para campos acima de 170 Td. Já o parâmetro na mistura com n-butano é intermediário entre os valores obtidos para o dióxido de carbono e o nitrogênio. Os resultados experimentais, disponíveis em forma tabular, foram comparados com os simulados utilizando o programa Magboltz 2, evidenciando boa concordância dentro da incerteza experimental.Artigo IPEN-doc 23868 Experimental and MCNP studies of paraffin and polyethylene in neutron moderation and BF3 detector efficiency2013 - 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.Artigo IPEN-doc 23875 Am-Be neutron irradiator used for nuclear instrumentation training2013 - 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.Artigo IPEN-doc 23996 Measurement of the first Townsend ionization coefficient in a methane-based tissue-equivalent gas2017 - PETRI, A.R.; GONÇALVES, J.A.C.; MANGIAROTTI, A.; BOTELHO, S.; BUENO, C.C.Tissue-equivalent gases (TEGs), often made of a hydrocarbon, nitrogen, and carbon dioxide, have been employed in microdosimetry for decades. However, data on the first Townsend ionization coefficient (α) in such mixtures are scarce, regardless of the chosen hydrocarbon. In this context, measurements of α in a methanebased tissue-equivalent gas (CH4 – 64.4%, CO2 – 32.4%, and N2 – 3.2%) were performed in a uniform field configuration for density-normalized electric fields (E/N) up to 290 Td. The setup adopted in our previous works was improved for operating at low pressures. The modifications introduced in the apparatus and the experimental technique were validated by comparing our results of the first Townsend ionization coefficient in nitrogen, carbon dioxide, and methane with those from the literature and Magboltz simulations. The behavior of α in the methane-based TEG was consistent with that observed for pure methane. All the experimental results are included in tabular form in the Supplementary material.Resumo IPEN-doc 23671 Density- normalized first Townsend ionization coefficients in a CH4-based tissue-equivalent gas mixture2016 - PETRI, A.R.; MANGIAROTTI, A.; GONÇALVES, J.A.C.; BUENO, C.C.Since 1950 methane-based tissue-equivalent gas (TEG) mixtures have been employed at low pressure in gaseous microdosimeters, such as tissue-equivalent proportional counters. Nevertheless, values of the first Townsend ionization coefficient (α) for these mixtures are scarce in the literature. In this work measurements of α as a function of the density-normalized electric field (E/N) were carried out in a methane-based TEG (CH4 - 64.4%, CO2 - 32.4% and N2 - 3.2%) in the range 100-300Td. The values of α were obtained using the Pulsed Townsend Technique by measuring the current growth as a function of the electric field strength in a Resistive Plate Chamber structure. Because of the parallel plate geometry, the field is uniform in our setup. As far as the authors are aware, there is only one set of experimental data on α for CH4-TEG published by Schmitz and Booz for reduced field strengths between 110V.cm-1.torr-1 (≈ 315Td) and 1780V.cm-1.torr-1 (≈ 5045Td). However, they employed a cylindrical proportional counter where α /p values were gathered from measurements of the gas gain resulting from an interval of electric field strengths. Because there are no data on α in methane-based TEG in the E/N range herein investigated, our results were compared with those expected from Magboltz simulations. Good agreement was found between experimental and simulated values of density-normalized α.Artigo IPEN-doc 22200 Experimental and MCNP studies of neutron moderators and BF detector efficiency2015 - CARDENAS, J.P.N.; MADI FILHO, T.; PEREIRA, M.C.C.; PETRI, A.R.Artigo IPEN-doc 21061 A modified setup for measuring the first ionization coeficient of tissue equivalent gases at low pressure2015 - PETRI, ANNA R.; GONCALVES, JOSEMARY A.C.; MANGIAROTTI, ALESSIO; BUENO, CARMEN C.Artigo IPEN-doc 17009 Technique of measuring the first ionization coefficient in gases2011 - LIMA, I.B.; VIVALDINI, T.C.; MANGIAROTTI, A.; PETRI, A.R.; GONCALVES, J.A.C.; BOTELHO, S.; FONTE, P.; BUENO, C.C.