Ao meu orientador Prof. Dr. Luiz Carlos Chamon, sou grato pela excelente orientação e por ter tornado todo o desenvolvimento deste trabalho uma atividade bastante agradável. Aos meus pais, Sérgio A. de A. Nobre e Esperança E. P. de A. Nobre, e irmão, Henrique P. de A. Nobre, pelo convívio e pelo constante apoio e incentivo à minha educação, em especial ao meu pai, com quem sempre pude discutir inúmeros assuntos, ligados a Física ou não. À minha noiva Ana Elisa Polloni por ser tão especial e por

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... ter sempre estado do meu lado, transformando sempre os momentos mais difíceis nos momentos mais felizes da minha vida. Ao meu tio Hermon Antonio de A. Nobre pelas primeiras aulas de Física, vinte anos atrás. Ao Prof. Dr. Brett V. Carlson pelas sempre pertinentes sugestões. vii viii Nascimento, que me ajudaram na caminhada até aqui, compartilhando muitos momentos alegres. Abstract In this Ph.D. thesis two theoretical models (ZPM and GFA) were proposed in order to obtain fusion cross sections and one (ZPM) to calculate the polarization potential for the elastic channel and the corresponding scattering cross section. The São Paulo (SP) potential, which has as one of its main characteristics the complete absence of adjustable parameters, was used as bare interaction in the calculations of the present work. Therefore, all results, presented in the context of different models, correspond to theoretical predictions instead of simply data fit. After a comparative analysis of fusion calculations, the GFA and ZPM models demonstrated to be equivalents and compatible with the usual coupled channel calculations, with the advantage of incorporating inelastic couplings to the complete vibrational band and of providing accurate fusion cross sections at extreme low energies relative to the Coulomb barrier. We applied the ZPM model to the calculation of the fusion excitation function for 112 heavy-ion systems, involving not only even-even nuclei but also odd-even and odd-odd ones (including some weakly-bound nuclei), and we compared the theoretical results with experimental data existing in literature. While the usual non-deformed barrier penetration model provides enhancements up to eleven orders of magnitude, the ZPM model predictions are in good agreement with the data within only two orders of magnitude. When confronting the ZPM model results with experimental data of elastic scattering cross sections for some systems, at energies around the Coulomb barrier, we found out good agreement between them. Therefore, we demonstrated that it is possible to treat the elastic scattering and fusion channels in a consistent manner, within the same context.