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[en] Purpose: Use the methodology developed by the National Research Council Canada (NRC), for Fricke Dosimetry, to determine the G-value used at Ir-192 energies. Methods: In this study the Radiology Science Laboratory of Rio de Janeiro State University (LCR),based the G-value determination on the NRC method, using polyethylene bags. Briefly, this method consists of interpolating the G-values calculated for Co-60 and 250 kV x-rays for the average energy of Ir-192 (380 keV). As the Co-60 G-value is well described at literature, and associated with low uncertainties, it wasn’t measured in this present study. The G-values for 150 kV (Effective energy of 68 keV), 250 kV (Effective energy of 132 keV)and 300 kV(Effective energy of 159 keV)were calculated using the air kerma given by a calibrated ion chamber, and making it equivalent to the absorbed to the Fricke solution, using a Monte Carlo calculated factor for this conversion. Instead of interpolations, as described by the NRC, we displayed the G-values points in a graph, and used the line equation to determine the G- value for Ir-192 (380 keV). Results: The measured G-values were 1.436 ± 0.002 µmol/J for 150 kV, 1.472 ± 0.002 µmol/J for 250 kV, 1.497 ± 0.003 µmol/J for 300 kV. The used G-value for Co-60 (1.25 MeV) was 1,613 µmol/J. The R-square of the fitted regression line among those G-value points was 0.991. Using the line equation, the calculate G-value for 380 KeV was 1.542 µmol/J. Conclusion: The Result found for Ir-192 G-value is 3,1% different (lower) from the NRC value. But it agrees with previous literature results, using different methodologies to calculate this parameter. We will continue this experiment measuring the G-value for Co-60 in order to compare with the NRC method and better understand the reasons for the found differences

[en] Metrology laboratories are expected to maintain standardized radiation beams and traceable standard dosimeters to provide reliable calibrations or testing of detectors. Results of the characterization of an x-ray system for performing calibration and testing of radiation dosimeters used for individual monitoring are shown in this work. (paper)

[en] The Fricke dosimeter is the most used, liquid chemical dosimeter. It has been shown to be a feasible option for the absorbed dose standard. The present work aims to determinate a dose-response curve of Fricke solution using different doses and reproducibility test comparing the calculated dose to Fricke solution and Ionizing Chamber. Tests were performed using an X-ray irradiator for biological research at Radiological Science Laboratory (LCR/UERJ). The results showed a linear response to different doses of type A uncertainties from 0.08 to 1.2%. Reproducibility test showed type A uncertainties of 0.16% to the dosimeter. (paper)

[en] The Fricke dosimeter is the most used liquid chemical dosimeter. High dose rate (HDR) brachytherapy using 192Ir sources is an important treatment option and it has been shown to be a feasible option for the absorbed dose standard. One of the parameters used to determine the absorbed dose at the Fricke solution is the G-value. This parameter is crucial and can be defined as the number of molecules of Fe+3 produced per Joule of energy absorbed in the solution. Few authors have determined the G-value for energies below the 60Co. Most part of papers on the literature compare the G-value to 60Co and different beam qualities. The G-value for energies lower than Co-60 are not well defined, some authors obtained it through calorimetric measurements and others the G(Fe3+) was obtained from the empirical formalism based on the primary products and Linear energy transfer (LET) values. The present work aim to determinate the G-value for 192Ir HDR using a new setup elaborated by Radiological Sciences Laboratory group (LCR/UERJ-Rio de Janeiro State University, Rio de janeiro, Brazil). It was performed using a HDR brachytherapy using 192Ir source (GammaMed Plus HDR 232, Varian) at Radiotherapy department of HUCFF - Hospital Universitário Clementino Fraga Filho, Rio de Janeiro, Brazil. The results showed a good statistical response to doses about 22 Gy and dose rates of and the G value calculated was 1.5607·10-6 Plus- Minus Sign·0.0669·10-6 mol.J-1 and type A uncertanty 0.96%.

[en] Pulsar timing has enabled some of the strongest tests of fundamental physics. Central to the technique is the assumption that the detected radio pulses can be used to accurately measure the rotation of the pulsar. Here, we report on a broadband variation in the pulse profile of the millisecond pulsar J1643−1224. A new component of emission suddenly appears in the pulse profile, decays over four months, and results in a permanently modified pulse shape. Profile variations such as these may be the origin of timing noise observed in other millisecond pulsars. The sensitivity of pulsar-timing observations to gravitational radiation can be increased by accounting for this variability.