The nuclear resonance parameters and the capture cross section of the neutron magic isotope 139La and of the radioactive isotope 151Sm have been measured relative to 197Au in the energy range of 0.6 eV-1 MeV at neutron time-of-flight (n_TOF) facility at CERN. The description of the experimental apparatus is followed by the presentation of the data analysis procedures consisting in the efficiency correction by means of the Pulse Height Weighting Function technique, in the determination of different background components and in their subtraction. We extracted the resonance parameters and the related nuclear quantities such as the resonance integral, the average gamma width, the nuclear level densities and the neutron strength function. These results improve the accuracy of the existing data. The deduced values of the Maxwellianaveraged capture cross section, together with the most recent spectroscopic observations in low metallicity stars, provide key indications for modelling the nucleosynthesis and the chemical evolution of heavy nuclei in the Galaxy.