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Made available in DSpace on 2015-03-03T15:15:30Z (GMT). No. of bitstreams: 1 FlavioMVS_DISSERT.pdf: 786675 bytes, checksum: 15c59d932af3a41769e781bb08d4e3e9 (MD5) Previous issue date: 2014-04-24 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The study of solar neutrinos is very important to a better comprehension of the set of nuclear reactions that occurs inside the Sun and in solar type stars. The ux of neutrinos provides a better comprehension of the stellar structure as a whole. In this dissertation we study the ux of neutrinos in a solar model, addressing the neutrino oscillation, analyzing with the intention of determining and verify the distribution from a statistical point of view, since this ux depends on the particles intrinsic velocity distributions in stellar plasma. The main tool for this analysis was the Toulouse-Geneva Stellar Evolution Code, or TGEC, which allow us to obtain the neutrino ux values per reaction and per layer inside the Sun, allowing us to compare the observational results for the neutrino ux detected on experiments based on Cl37 (Homestake), Ga71 (SAGE, Gallex/GNO) and water (SNO). Our results show the nal distribution for neutrino ux as a function of the depth using the coordinates of mass and radius. The dissertation also shows that the equations for this ux are present in TGEC. / O estudo do neutrino solar ? muito importante para uma melhor compreens?o sobre o conjunto de rea??es nucleares que ocorrem no interior do Sol e nas estrelas do tipo solar. O fluxo de neutrino tamb?m proporciona uma melhor compreens?o da estrutura estelar como um todo. Nesta disserta??o, estudamos o fluxo de neutrinos em um modelo Solar, abordando a oscila??o de neutrinos, analisando com intuito de determinar e verificar a distribui??o do fluxo do ponto de vista estat?stico, uma vez que este fluxo depende das distribui??es intr?nsecas de velocidades das part?culas no plasma estelar. A principal ferramenta desta analise foi o c?digo de evolu??o estelar Toulouse-Geneva (Stellar Evolution Code, ou TGEC), o qual permite-nos obter os valores do fluxo de neutrino por rea??o e por camada no interior do Sol, e assim podemos comparar com os resultados observacionais para o fluxo de neutrino detectado a partir de experimentos com base no Cl37 (Homestake), Ga71 (SAGE, Gallex/GNO) e agua (SNO). Nosso resultado mostra a distribui??o final para o fluxo de neutrinos em fun??o da profundidade em coordenadas de massa e raio. A referida disserta??o apresenta ainda as equa??es relacionadas com este fluxo que est?o presentes no TGEC

High precision measurements of a weak interaction decay were conducted to search for possible variation of the decay rate parameter caused by an antineutrino flux. The experiment searched for variation of the ⁵⁴Mn electron capture decay rate parameter to a level of precision of 1 part in ∼10⁵ by comparing the difference between the decay rate in the presence of an antineutrino flux ∼3×10¹² cm^-2sec^-1 and no flux measurements. The experiment is located 6.5 meters from the reactor core of the High Flux Isotope Reactor (HFIR) in Oak Ridge National Laboratory. A measurement to this level of precision requires a detailed understanding of both systematic and statistical errors. Otherwise, systematic errors in the measurement may mimic fundamental interactions. <div><br></div><div>The gamma spectrum has been collected from the electron capture decay of ⁵⁴Mn. What differs in this experiment compared to previous experiments are, (1) a strong, uniform, highly controlled, and repeatable source of antineutrino flux, using a reactor, nearly 50 times higher than the solar neutrino flux on the Earth, (2) the variation of the antineutrino flux from HFIR is 600 times higher than the variation in the solar neutrino flux on the Earth, (3) the extensive use of neutron and gamma-ray shielding around the detectors, (4) a controlled environment for the detector including a fixed temperature, a nitrogen atmosphere, and stable power supplies, (5) the use of precision High Purity Germanium (HPGe) detectors and finally, (6) accurate time stamping of all experimental runs. By using accurate detector energy calibrations, electronic dead time corrections, background corrections, and pile-up corrections, the measured variation in the ⁵⁴Mn decay rate parameter is found to be δλ/λ=(0.034±1.38)×10^-5. This measurement in the presence of the HFIR flux is equivalent to a cross-section of σ=(0.097±1.24)×10^-25cm². These results are consistent with no measurable decay rate parameter variation due to an antineutrino flux, yielding a 68% confidence level upper limit sensitivity in δλ/λ <= 1.43×10^-5 or σ<=1.34×10^-25cm² in cross-section. The cross-section upper limit obtained in this null or no observable effect experiment is ∼10⁴ times more sensitive than past experiments reporting positive results in ⁵⁴Mn.</div>