Résumé : Intense N13 radioactive ion beams have been produced by the two-accelerator method. They have been used to investigate the N13(p,)14O reaction, in particular to measure directly its cross section in the energy region of interest in nuclear astrophysics. The results of a complete set of experiments thereby carried out on this reaction allowed the determining of the stellar conditions under which the cold and hot CNO cycles, for the nuclear burning of hydrogen and its transformation into helium, dominate. © 1993 The American Physical Society.