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137 páginas. Tesis Doctoral del Departamento de Física Atómica, Molecular y Nuclear de la Universidad de Valencia y del Instituto de Física Corpuscular (IFIC)., The measurement of the (n, ) cross section of 54Fe and 57Fe isotopes was performed at the CERN n_TOF facility with the aim of better understanding the s-process stellar nucleosynthesis in the Fe-Ni region. At the same time Fe is a structural material in accelerator driven systems (ADS) and accurate neutron cross sections are required for reliable design studies, to account for the neutron balance and for assessing the related uncertainties. The accurate measurement of the (n,gamma ) cross section of 54Fe and 57Fe isotopes in the resolved resonance region (RRR) has been carried out with high resolution using the time of ight technique. These measurements were performed using the total energy detector technique. An optimized detection setup has been used, which permitted the determination of their cross sections with a minimal in uence of neutron sensitivity. First part of this work was devoted to the MC simulation of the response function to calculate the corresponding weighting functions. These weighting functions were applied to the measured data in order to obtain the capture yield, and derive the capture cross section. An R-matrix analysis of the resolved resonance region has been performed for both nuclides, deriving the total radiative capture cross section and the corresponding resonance parameters. The analysis was carried out using the R-matrix code SAMMY. The results obtained in this work are compared with previous experiments performed elsewhere and with evaluated data. The results presented in this work are important to disentangle the r and s contribution observed in the old stars and for advanced reactor concepts.