Sobre a composição química em estrelas evoluídas do aglomerado aberto M67

The Galaxy open clusters have a wide variety of physical properties that make them valuable laboratories for studies of stellar and chemical evolution of the Galaxy. In order to better settle these properties we investigate the abundances of a large number of chemical elements in a sample of 27 evolved stars of the open cluster M67 with different evolutionary stages (turn-off, subgiant and giant stars). For such a study we used high-resolution spectra (R 47 000) and high S/N obtained with UVES+FLAMES at VLT/UT2, covering the wavelength interval 4200-10 600 Å. Our spectral analysis is based on the MARCS models of atmosphere and Turbospectrum spectroscopic tool. The oxygen abundances were determined from the [O I] line at 6300 Å. In addition, we have also computed abundances of Si I, Na I, Mg I, Al I, Ca I, Ti I, Co I, Ni I, Zr I, La II and Cr I. The abundances investigated in this work, combined with their stellar parameters, offers an opportunity to determine the level of mixing and convective dilution of evolved stars in M67. Based on the obtained parameters, the abundances of these seem to follow a similar trend to the curve of solar abundances. Additionally, following strategies of other studies have investigated the relative abundances as a function of effective temperature and metallicity, where it was possible to observe an abundance of Na, Al and Si to the stars in the field of giants. A large dispersion from star to star, is observed in the ratios [X / Fe] for the Co, Zr and La, and the absence of Zr and La, in the stars of the turn-off. Comparisons made between our results and other studies in the literature show that values of abundances are in agreement and close to the limits of the errors

A física da terapia de captura de nêutrons pelo boro

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Avaliação das técnicas TDR (Reflectometria por Domínio do Tempo) e moderação de nêutrons, na determinação do teor de água em diferentes classificações do solo

Pós-graduação em Agronomia (Energia na Agricultura) - FCA

Geocronologia por traço de fissão em apatitas de rochas alcalinas: comparação dos diferentes métodos de datação e calibração da dosimetria de nêutrons

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Da roseta as estrelas: um debate sobre a representação feminina na marinha brasileira

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Confecção e caracterização de filmes finos de boro para a medida da taxa de reação 10B(N, a)7LI na terapia por captura de nêutrons pelo boro

The Boron Neutron Capture Therapy (BNCT), based on the 10B(n,α)7Li reaction, represents a promising modality for the treatment of cancers that are resistents to conventional treatments. So, it is necessary to find drugs (boron compounds) with high selectivity for each type of cancer, the neutrons source should be well characterized and the rate of 10B(n,α)7Li reaction should be measured with great accuracy as possible. This study aimed to develop a method for manufacturing thin films of boron, for measure the 10B(n,α)7Li reaction, and analyze the uniformity of the films. Five thin films of boron were manufactured with three different concentrations of boric acid, heated to transform the acid in boron, irradiated with thermic neutrons coupled to CR-39 detectors, in BNCT line at the reactor IEA-R1 IPEN/CNEN, São Paulo. After the irradiation, the detectors were chemically attacked with NaOH to reveal the tracks. The methodology presented is effective because it resulted in deposition of boron as thin film enabling the quantitative analysis of 10B(n,α)7Li reaction. The analysis of the uniformity of density of the induced tracks in CR-39 shows that, in most of the films, there is no uniformity in surface distribution of boron, but when the film is divided, we obtain some uniform sectors

Produção do monóxido de titânio em estrelas variáveis

Mira are pulsating variable stars in advanced stages of evolution. Their atmospheres are sources of intense absorption bands attributed to molecular titanium monoxide (TiO). It has been suggested that the abundance of TiO reaches its maximum value near the minimum light. In this sense, the study of the processes of formation and destruction of TiO in circumstellar envelopes of Mira stars, not only allows us to understand the physical and chemical processes that occur in these environments, as it allows to verify the correlation between the abundance of TiO and its light curve. However, the main mechanisms of formation and destruction of TiO are poorly known and, consequently, the possible correlation between the abundance of this species and the light curve. In these sense, we studied the main processes of formation and destruction of titanium monoxide in molecular layers of Mira atmospheres and determined its temporal variation as function of the stellar radius. The TiO profile along the radius was expected for the different stellar phase, however its abundance is not enough to explain the light curve. The reasons behind it are discussed in details

Determinação de elementos traços em diques mesozoicos da Serra do Mar por meio de ativação com nêutrons

A análise de elementos traço, tais como terras raras, TH, U, Ta, Hf, Ba, Rb e Ba, é uma ferramenta muito importante para estudos petrogenéticos. No intuito de estudar tais processos em diques do Enxame Serra do Mar (litoral de São Paulo e Rio de Janeiro), pertencente à Provincia Magmática do Paraná (PMP), uma das províncias de basaltos continentais mais expressivas do mundo, foram realizadas análises por ativação com nêutrons nestes diques. A técnica, empregada no Centro de Reator de pesquisa do Instituto de Pesquisas Energéticas e Nucleares, forneceu concentrações de elementos traço com os níveis de precisão de 10% e exatidão 9% os quais são adequadas para estudos petrogenéticos. Devido as baixas concentrações dos elementos analisados, a rotina experimental de preparação das amostras abrangeu processos bastantes cuidadosos para evitar contaminação. As amostras investigadas podem ser divididas em quatro grupos: rochas básicas (SiO2<55%) com Ti/Y<500; rochas intermediárias (55%63%). Diques de composição intermediária e ácida só ocorrem na Ilha de São Sebastião e na região costeira adjacente. As concentrações de elementos maiores e menores, bem como os padrões de abundância de terras raras e de outros elementos incompatíveis dessas rochas mais diferenciadas, apresentaram semelhanças significativas com os das vulcânicas Chapecó do tipo Ourinhos, sugerindo gênese similar, ou seja, incluindo também processos de contaminação crustal .