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.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 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.Artigo IPEN-doc 18317 Secondary effect on electron multiplication in pure isobutane2012 - MANGIAROTTI, A.; LIMA, I.B.; VIVALDINI, T.C.; GONCALVES, J.A.C.; PETRI, A.R.; BOTELHO, S.; FONTE, P.; BUENO, C.C.