https://ri.ufs.br/jspui/handle/riufs/2560 2026-05-01T11:40:16Z https://ri.ufs.br/jspui/handle/riufs/24019 Título: Caracterização física de partículas de radiação através de uma câmara de nuvens de difusão Autor(es): Costa, David Goes Abstract: Nuclear radiation is a phenomenon linked to the quantum nature of the processes occurring in the atomic nucleus, which leads to the release of various particles, aiming to bring nuclei to a state of lower energy. The energy scales involved in this process are on the order of 106 eV, so the particle that emerges from the decay carries this magnitude of energy. Due to the diverse applications and risks associated with the interaction of such particles with the environment and living beings, characterizing the emissions of radioactive nuclides is of immense importance. This work sought to build a diffusion cloud chamber, allowing the observation of trails left by the passage of radiation particles through the medium. To arrive at a functional version of the chamber, different arrangements of the apparatus, cooling agents and substances for cloud formation were tested. The radiation sources used in this work were collimated alpha radiation, from americium-241, and beta radiation, from cesium-137. The particle characterization was performed qualitatively through analysis of recorded images of their tracks, which showed significant differences in the energy deposition rates, as well as mass, between alpha and beta particles. Using literature data on the energy deposition rates of these particles in a medium similar to that of the chamber, it was also possible to calculate the initial kinetic energy of the alpha particles, whose frequency distribution for small time intervals resembles that expected for the quantized energy levels of the americium-241 nucleus, with apparent energy loss over the operating time of the apparatus possibly due to the particles’ interactions with the changing chamber environment. 2025-09-25T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/23694 Título: Um estudo do parâmetro de viscosidade do disco da estrela Be ABE A26 Autor(es): Vasconcelos, Letícia Rocha Abstract: Although viscosity plays a fundamental role in the diffusion of astrophysical disks, we are still unable to derive its properties theoretically from first principles. Therefore, the search for observational constraints on its behavior represents an important step towards its understanding. In this work, we investigated the viscosity parameter (α) of the disk around the Be star ABE A26 (MWC 109), to place empirical constraints on it and examine its temporal variability. We used the star’s spectral energy distribution (SED) and photometric data from the KELT project. By fitting the SED, we determined stellar parameters such as mass, equatorial-to-polar radius ratio, distance, among other parameters relevant to disk modeling. These fits yielded values consistent with the literature, including a mass of 10.0 ± 1.0M⊙ and a radius ratio of 1.36±0.20. We then modeled the light curve at six different epochs of disk formation/dissipation using simulated disk scenarios with the hydrodynamic code SINGLEBE. The main results of this analysis include values of logα between 0.15 and 0.55, and logΣ0[g cm−2 ] (disk base density) between −0.40 and 0.87. The viscosity parameter values found are slightly higher than those typically reported in the literature, which may be a consequence of the short disk development timescales. As future work, we intend to study the initial outbursts of this object observed by KELT, whose early magnitudes are brighter than those of the events analyzed here. Finally, we plan to apply the methodology developed in this study to the full sample of Be stars observed by the KELT mission, and, eventually, to other observational surveys. 2025-09-17T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/23693 Título: Estudo das propriedades estruturais e eletrônicas de semicondutores (GaAs, SiC e Si) via Teoria do Funcional da Densidade (DFT) Autor(es): Silva, Walace Ferreira Macedo da Abstract: Density Functional Theory (DFT) is a powerful and widely used computational tool for investigating the properties of materials at the atomic level. Its ability to provide detailed information about the electronic structure and other physical properties of materials makes it an indispensable tool in materials science and solid-state physics. The aim of this work was to determine the structural and electronic properties of some semiconductors. The combination of technical skills in Linux/UNIX and Fortran 90, along with specific training in the Wien2k software, enabled accurate and comprehensive simulations in the advanced study of materials physics. The training included the simulation and optimization of the crystalline structure of semiconductor materials (Si, SiC, and GaAs), self-consistent calculation of their electronic structures, as well as analysis and interpretation of the obtained results. Different exchangecorrelation functionals were compared, including the Local Density Approximation (LDA), the Generalized Gradient Approximation (GGA) parametrized by Perdew-Burke-Ernzerhof (PBEGGA), and its solid-state modification (GGA-PBESOL). The results obtained showed good agreement with values found in the literature regarding lattice parameters and electronic properties. However, for a more accurate prediction of the bandgap, it was necessary to introduce the modified Becke-Johnson (mBJ) potential correction in some compounds, resulting in values closer to the experimental ones. 2025-09-18T00:00:00Z https://ri.ufs.br/jspui/handle/riufs/23544 Título: A variabilidade de estrelas Be vista por espectroscopia no ultravioleta Autor(es): Ximenes, Sabrina Nantua Abstract: Be stars are a type of main-sequence star that, at some point, have undergone mass ejection into a circumstellar environment. They are also known for their high rotational velocities and the presence of emission lines in their spectra, the latter caused by the circumstellar disk formed from the ejected material. However, the mechanism responsible for this ejection is still not well understood. The International Ultraviolet Explorer (IUE) was a space telescope that operated from 1978 to 1996, collecting data in the ultraviolet region and observing, among other objects, Solar System bodies, active galactic nuclei, and hot stars, including Be stars. The present work aims to quantify the spectral variations in IUE data for a large sample of Be stars in the ultraviolet, through an empirical analysis of their spectral properties, which are directly linked to circumstellar mass ejection. For this purpose, 94 Be stars were selected from the Database of Be Star Spectra (BeSS), filtering those objects with IUE spectra that have at least three observations in both the near- and far-ultraviolet regions. Temporal variations in flux levels and spectral indices were analyzed, as well as the correlations between these quantities. Additionally, for each object, the mean and standard deviation of the measured quantities were calculated. Finally, possible correlations between the observed variations and both spectral subtype and projected rotational velocity were investigated. The results show that earlier-type Be stars display greater variability than later-type ones. Furthermore, there is a significant contribution from the disk in the ultraviolet spectrum, with a behavior similar to that observed in other regions of the electromagnetic spectrum. 2025-09-18T00:00:00Z