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[en] An accurate determination of the true null distance between electrodes, that defines the sensitive volume of an extrapolation chamber, is critical for the establishment of a primary measurement method for absorbed dose in tissue. In this work, a critical analysis of two methodologies for determining the true null electrode spacing of a 23392 Böhm model PTW extrapolation chamber was done. (paper)

[en] The purpose of this study was to obtain real contact areas, forces, and pressures acting on human dental enamel as a function of the nominal pressure during dental occlusal contact. The described development consisted of three steps: characterization of the surface roughness by 3D contact profilometry test, finite element analysis of micro responses for each pair of main asperities in contact, and homogenization of macro responses using an assumed probability density function. The inelastic deformation of enamel was considered, adjusting the stress-strain relationship of sound enamel to that obtained from instrumented indentation tests conducted with spherical tip. A mechanical part of the static friction coefficient was estimated as the ratio between tangential and normal components of the overall resistive force, resulting in μ_d = 0.057. Less than 1% of contact pairs reached the yield stress of enamel, indicating that the occlusal contact is essentially elastic. The micro-models indicated an average hardness of 6.25GPa, and the homogenized result for macroscopic interface was around 9GPa. Further refinements of the methodology and verification using experimental data can provide a better understanding of processes related to contact, friction and wear of human tooth enamel.

[en] The Monte Carlo Modelling Expert Group (MCMEG) is an expert network specializing in Monte Carlo radiation transport and the modelling and simulation applied to the radiation protection and dosimetry research field. In the first inter-comparison the group launched an exercise to model and simulate a 6 MV LINAC photon beam using several Monte Carlo codes. Experimental measurements carried out in the National Cancer Institute (INCA) in Rio de Janeiro, Brazil, were used to validate the models and simulated results. Now, the group has launched a second inter-comparison exercise for modeling and simulating a radiotherapy treatment planning for prostate cancer. The goal is obtained the dose distribution in the target organ and the neighboring organs. Validation of the computational models were carried out using experimental measurements performed with an Alderson phantom in a hospital in BH/MG, Brazil. This paper reports in detail the modeling process using MCNPx, MCNP6, EGSnrc and Penelope Monte Carlo codes, the source and tally descriptions, the validation processes and the results.