The fragmentation of a 133 pps beam of 14Be ions at 35 MeV/A on targets of carbon and lead has been used to study the structure of the unbound nucleus 13Be. Neutrons and 12Be reaction products were measured in the DeMoN array and a detector telescope placed at 0° respectively. These coincidence measurements were used to reconstruct the 13Be particles. The beam energy was measured on a particle by particle basis from the time of flight. This was essential for momentum measurements which were made in the reference frame of the projectile. A significant contribution to the experimental background came from reactions in the detector telescope, which had to be subtracted. Relative velocity (arithmetic velocity difference) and invariant mass analyses both signify the existance of significant strength close to the 12Be + n threshold. Simulations including an experimental filter clearly show that this includes strength that is localised below 500 ke V in relative energy. Momentum distributions for 12Be, 10Be, neutrons and the reconstructed 13Be particle in the longitudinal direction have been measured. The 13Be distribution displays evidence for a two component structure. Calculations of the neutron stripping from 14Be have shown that this structure requires s-wave stripping to explain the narrow component. The wider component is consistent with d- wave stripping, and additional contributions from p-wave stripping cannot be excluded. The angular distribution of neutrons from 12Be + n breakup, measured in the 13Be reference frame is essentially isotropic. There is evidence for a weak asymmetry which could be due to broad over-lapping states of both positive and negative parity at energies below 2 MeV. This would support the inclusion of a P½ resonance in the low-lying structure of 13Be.

Le déploiement des futurs réacteurs à neutrons rapides, dits de Génération IV, est porteur d'améliorations prometteuses sur le plan de l'utilisation des matières premières et de la gestion des déchets. Elles s'accompagneront d'une transformation majeure du cycle et du développement de nouveaux procédés de recyclage, plus simples et plus efficaces. Une des conséquences de cette évolution est l’augmentation de la quantité de radionucléides à vie longue (RNVL) le carbone 14, l’iode 129 et le chlore 36 dans le combustible irradié, rejets du cycle nucléaire. La maîtrise et la réduction de ces rejets passe d’abord par une meilleure connaissance de la quantité de ces radionucléides dans le combustible, formés pendant son irradiation en réacteur. Ce travail de thèse s’inscrit dans l’objectif d’améliorer la mesure des radionucléides carbone 14, iode 129 et chlore 36 dans l’oxyde irradié, non seulement sur les performances analytiques mais aussi sur la minimisation des volumes de rejets liquides et solides engendrés. Une étude bibliographique a été menée afin d’établir le bilan des méthodes existantes pour la mesure de ces RNVL dans l’oxyde irradié. Les conclusions de cette étude ont orienté ce travail selon trois axes principaux : l’utilisation de l’ozone pour oxyder et désorber le carbone 14 de l’oxyde irradié après sa mise en solution ; la proposition d’une méthode d’extraction sélective du chlore 36 contenu dans l’oxyde irradié ; le développement d’une nouvelle méthode d’analyse alliant une séparation par chromatographie ionique couplée à une détection des émetteurs R par scintillation solide pour les trois RNVL / The deployment of future fast neutron reactors, called Generation IV, carries promising improvements in the use of raw materials and waste management. They will lead to a major transformation of the cycle and the development of new recycling processes which will be simplified and more effective. One consequence of this development is the increase of the amount of long-lived radionuclides in spent fuel nuclear waste: 14 carbon, 129 iodine and 36 chlorine. The control and reduction of these radionuclides begins with a better understanding of the amount of these radionuclides in the spent fuel, generated during irradiation in a reactor. The objective of this work consist in improving the measurement of 14 carbon , 129 iodine and 36 chlorine radionuclides in the irradiated oxide, all in reducing the liquid and solid waste generated. A bibliography study was conducted to evaluate the existing methods for measuring these radionuclides in irradiated oxide. The conclusions of this study have oriented the work in three main ways: the use of ozone to oxidize and desorb 14 carbon of the irradiated oxide after solution treatment; the proposal of a selective extraction method for 36 chlorine contained in the irradiated oxide; the development of a new analytical method combining a separation by ion chromatography coupled with detection of R solid scintillation for the three radionuclides