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The beta decay of the neutron-rich In-134 and In-135 was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z = 50 above the N = 82 shell. The beta-delayed gamma-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three beta-decay branches of In-134 were established, two of which were observed for the first time. Population of neutron-unbound states decaying via gamma rays was identified in the two daughter nuclei of In-134, Sn-134 and Sn-133, at excitation energies exceeding the neutron separation energy by 1 MeV. The beta-delayed one-and two-neutron emission branching ratios of In-134 were determined and compared with theoretical calculations. The beta-delayed one-neutron decay was observed to be dominant beta-decay branch of In-134 even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of Sn-134. Transitions following the beta decay of In-135 are reported for the first time, including gamma rays tentatively attributed to Sn-135. In total, six new levels were identified in Sn-134 on the basis of the beta gamma gamma coincidences observed in the In-134 and In-135 beta decays. A transition that might be a candidate for deexciting the missing neutron single-particle 13/2(+) state in Sn-133 was observed in both beta decays and its assignment is discussed. Experimental level schemes of Sn-134 and Sn-135 are compared with shell-model predictions. Using the fast timing technique, half-lives of the 2(+), 4(+), and 6(+) levels in Sn-134 were determined. From the lifetime of the 4(+) state measured for the first time, an unexpectedly large B(E2; 4(+) -> 2(+)) transition strength was deduced, which is not reproduced by the shell-model calculations.

The beta decay of the neutron-rich In-134 and In-135 was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z = 50 above the N = 82 shell. The beta-delayed gamma-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three beta-decay branches of In-134 were established, two of which were observed for the first time. Population of neutron-unbound states decaying via. rays was identified in the two daughter nuclei of In-134, Sn-134 and Sn-133, at excitation energies exceeding the neutron separation energy by 1 MeV. The beta-delayed one- and two-neutron emission branching ratios of In-134 were determined and compared with theoretical calculations. The beta-delayed one-neutron decay was observed to be dominant beta-decay branch of In-134 even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of Sn-134. Transitions following the beta decay of In-135 are reported for the first time, including. rays tentatively attributed to Sn-135. In total, six new levels were identified in Sn-134 on the basis of the beta.. coincidences observed in the In-134 and In-135 beta decays. A transition that might be a candidate for deexciting the missing neutron single-particle 13/2(+) state in Sn-133 was observed in both beta decays and its assignment is discussed. Experimental level schemes of Sn-134 and Sn-135 are compared with shell-model predictions. Using the fast timing technique, half-lives of the 2(+), 4(+), and 6(+) levels in Sn-134 were determined. From the lifetime of the 4(+) state measured for the first time, an unexpectedly large B(E2; 4(+)-> 2(+)) transition strength was deduced, which is not reproduced by the shell-model calculations.

Prompt and delayed gamma-ray spectroscopy of the neutron-rich Kr-94 was performed, as part of the fission campaign at the ALTO facility of the IPN Orsay, using the fast-neutron-induced fission reaction U-238(n, f) in combination with the nu-Ball array, a novel hybrid gamma spectrometer for energy and lifetime measurements. Several new yrast and nonyrast transitions were observed for the first time, extending the previously known level scheme. Additionally, we report on the observation of a new short-lived isomer at 3444 keV with a half-life of 32(3) ns. The analysis of the Nilsson orbitals obtained from Gogny cranked Hartree-Fock-Bogoliubov calculations suggests a (9(-)) spin and an oblate deformation for this isomer corresponding to a two-quasineutron state, indicating an isomeric structure very similar to that of the neighboring isotones Sr-96 and Se-92.

Excited states in the neutron-rich Se-85 nucleus have been studied using for the first time a fast neutron-induced fission of Th-232. The experiment was performed at the ALTO facility of the IPN Orsay. Coupling of the LICORNE directional neutron source with the nu-ball high-resolution gamma-ray spectrometer provided unique access to high-spin states in neutron-rich fission fragments from the Th-232(n,f) reaction. A preliminary level scheme of Se-85 was established by the analysis of prompt gamma-gamma-gamma coincidences. Identification of the all known yrast states in Se-85 is the first step towards studies of more neutron-rich Se isotopes.

Background: Odd-odd nuclei, around doubly closed shells, have been extensively used to study proton-neutron interactions. However, the evolution of these interactions as a function of the binding energy, ultimately when nuclei become unbound, is poorly known. The ²⁶F nucleus, composed of a deeply bound π 0d_(5/2) proton and an unbound ν0d_(3/2) neutron on top of an ²⁴O core, is particularly adapted for this purpose. The coupling of this proton and neutron results in a J^π= 1₁⁺ - 4₁⁺ multiplet, whose energies must be determined to study the influence of the proximity of the continuum on the corresponding proton-neutron interaction. The J^π = 1₁⁺, 2₁⁺, 4₁⁺ bound states have been determined, and only a clear identification of the J^π = 3₁⁺ is missing. Purpose: We wish to complete the study of the J^π = 1₁⁺ - 4₁⁺multiplet in ²⁶F, by studying the energy and width of the J^π = 3₁⁺unbound state. The method was first validated by the study of unbound states in ²⁵, for which resonances were already observed in a previous experiment. Method: Radioactive beams of ²⁶Ne and ²⁷Ne, produced at about 440AMeV by the fragment separator at the GSI facility were used to populate unbound states in ²⁵F and ²⁶F via one-proton knockout reactions on a CH₂ target, located at the object focal point of the R³B/LAND setup. The detection of emitted. γ and neutrons, added to the reconstruction of the momentum vector of the A - 1 nuclei, allowed the determination of the energy of three unbound states in ²⁵F and two in ²⁶F. Results: Based on its width and decay properties, the first unbound state in ²⁵F, at the relative energy of 49(9) keV, is proposed to be a J^π = 1/ 2ˉ arising from a p_(1/2) proton- hole state. In ²⁶F, the first resonance at 323(33) keV is proposed to be the J^π = 3₁⁺ member of the J^π = 1₁⁺- 4₁⁺multiplet. Energies of observed states in ²⁵ʼ²⁶F have been compared to calculations using the independent-particle shell model, a phenomenological shell model, and the ab initio valence-space in-medium similarity renormalization group method. Conclusions: The deduced effective proton- neutron interaction is weakened by about 30-40% in comparison to the models, pointing to the need for implementing the role of the continuum in theoretical descriptions or to a wrong determination of the atomic mass of ²⁶F.

Background: For many years, quasifree scattering reactions in direct kinematics have been extensively used to study the structure of stable nuclei, demonstrating the potential of this approach. The (RB)-B-3 collaboration has performed a pilot experiment to study quasifree scattering reactions in inverse kinematics for a stable C-12 beam. The results from that experiment constitute the first quasifree scattering results in inverse and complete kinematics. This technique has lately been extended to exotic beams to investigate the evolution of shell structure, which has attracted much interest due to changes in shell structure if the number of protons or neutrons is varied. Purpose: In this work we investigate for the first time the quasifree scattering reactions (p, pn) and (p, 2p) simultaneously for the same projectile in inverse and complete kinematics for radioactive beams with the aim to study the evolution of single-particle properties from N = 14 to N = 15. Method: The structure of the projectiles O-23, O-22, and N-21 has been studied simultaneously via (p, pn) and (p, 2p) quasifree knockout reactions in complete inverse kinematics, allowing the investigation of proton and neutron structure at the same time. The experimental data were collected at the (RB)-B-3-LAND setup at GSI at beam energies of around 400 MeV/u. Two key observables have been studied to shed light on the structure of those nuclei: the inclusive cross sections and the corresponding momentum distributions. Conclusions: The knockout reactions (p, pn) and (p, 2p) with radioactive beams in inverse kinematics have provided important and complementary information for the study of shell evolution and structure. For the (p, pn) channels, indications of a change in the structure of these nuclei moving from N = 14 to N = 15 have been observed, i.e., from the 0d(5/2) shell to the 1s(1/2). This supports previous observations of a subshell closure at N = 14 for neutron-rich oxygen isotopes and its weakening for the nitrogen isotopes.

Rapid shape evolutions near A = 100 are now the focus of much attention in nuclear science. Much of the recent work has been centered on isotopes with Z

Background: For many years, quasifree scattering reactions in direct kinematics have been extensively used to study the structure of stable nuclei, demonstrating the potential of this approach. The (RB)-B-3 collaboration has performed a pilot experiment to study quasifree scattering reactions in inverse kinematics for a stable C-12 beam. The results from that experiment constitute the first quasifree scattering results in inverse and complete kinematics. This technique has lately been extended to exotic beams to investigate the evolution of shell structure, which has attracted much interest due to changes in shell structure if the number of protons or neutrons is varied. Purpose: In this work we investigate for the first time the quasifree scattering reactions (p, pn) and (p, 2p) simultaneously for the same projectile in inverse and complete kinematics for radioactive beams with the aim to study the evolution of single-particle properties from N = 14 to N = 15. Method: The structure of the projectiles O-23, O-22, and N-21 has been studied simultaneously via (p, pn) and (p, 2p) quasifree knockout reactions in complete inverse kinematics, allowing the investigation of proton and neutron structure at the same time. The experimental data were collected at the (RB)-B-3-LAND setup at GSI at beam energies of around 400 MeV/u. Two key observables have been studied to shed light on the structure of those nuclei: the inclusive cross sections and the corresponding momentum distributions. Conclusions: The knockout reactions (p, pn) and (p, 2p) with radioactive beams in inverse kinematics have provided important and complementary information for the study of shell evolution and structure. For the (p, pn) channels, indications of a change in the structure of these nuclei moving from N = 14 to N = 15 have been observed, i.e., from the 0d(5/2) shell to the 1s(1/2). This supports previous observations of a subshell closure at N = 14 for neutron-rich oxygen isotopes and its weakening for the nitrogen isotopes.

Lifetimes of low-lying yrast states in neutron-rich Sr-94,Sr-96,Sr-98 have been measured by Germanium-gated gamma-gamma fast timing with LaBr3(Ce) detectors using the EXILL& FATIMA spectrometer at the Institut Laue-Langevin. Sr fission products were generated using cold-neutron-induced fission of 235U and stopped almost instantaneously within the thick target. The experimental B(E2) values are compared with results of Monte Carlo shell-model calculations made without truncation on the occupation numbers of the orbits spanned by eight proton and eight neutron orbits and show good agreement. Similarly to the Zr isotopes, the abrupt shape transition in the Sr isotopes near neutron number N = 60 is identified as being caused by many-proton excitations to its g(9/2) orbit.

Total absorption gamma-ray spectroscopy is used to measure accurately the intensity of gamma emission from neutron-unbound states populated in the β-decay of delayed-neutron emitters. From the comparison of this intensity with the intensity of neutron emission one can deduce information on the (n,γ) cross section for unstable neutron-rich nuclei of interest in r process abundance calculations. A surprisingly large gamma branching was observed for a number of isotopes. The results are compared with Hauser-Feshbach calculations and discussed.

Nuclei with few valence particles outside of a doubly-magic core provide valuable information about single-particle energies, nucleon-nucleon e_ective interactions and may give insight into the onset of collectivity. The region around 132Sn draws particular attention because of the unexpected modi_cations of the shell structure and the sudden collective behaviour that arises. The 136Te nucleus, with two protons and two neutrons coupled to the doubly-magic 132Sn (Z=50 and N=82) constitutes an excellent testing ground for the study of these phenomena, and so it is studied in this PhD thesis. One of the best means to study exotic nuclei is through lifetime measurements of excited states since they allow direct and model independent access to electromagnetic transition probabilities, which are key quantities for the study of single-particle configurations, nuclear collectivity, and make it possible to test theoretical models. Thus this PhD thesis investigates the 136Te nucleus through the lifetime measurements of its excited states...

Uno de los pilares fundamentales de la estructura nuclear, tal y como la conocemos de los nucleos estables, es la existencia de numeros magicos. Los nucleos mas estables surgen de orbitales completamente llenos, orbitales cerrados, y dan lugar a los nagicos. En el valle de estabilidad dichos numeros son 8, 20, 28, 50, 82 y 126. La constante evolucion en la produccion, separacion e identicacion de nucleos exoticos, junto a una mejora en las tecnicas de deteccion, hace posible el estudio experimental de nucleos lejos del valle de estabilidad. Estos nucleos exoticos con numero supuestamente magicos no siempre tiene las propiedades que uno esperara. Al ir añadiendo o sustrayendo nucleones de un nucleo estable, la energía de partícula independiente se modifican y fuertes correlaciones octupolares aparecen, las cuales pueden neutralizar los saltos de capa del campo medio esferico. La investigacion de la evolucion de la estructura de capas lejos de la estabilidad se ha convertido en uno de los temas mas importantes en Física Nuclear. Investigaciones en este area tienen grandes implicaciones en astrofísica nuclear, ya que los nucleos exoticos juegan un papel crucial en los procesos de nucleosíntesis estelar que dan lugar a la formacion de los nucleos presentes en el Universo. El experimento IS474 se realizo en las instalaciones ISOLDE, CERN, donde se crearon isotopos de 59-66 Mn y su desintegracion estudiada. Esta tesis doctoral se centra en el estudio de isotopos ricos en neutrones (los impares 63;65Fe y el par 66Fe) empleando espectroscopía gamma y estudios de coincidencias retardadas avanzadas...

The evolution of single-particle states in neutron-rich nuclei provides a key information on their nuclear structure and is an important ingredient for the development of nuclear models that can be applied to predict the structure at the borderline of nuclear map. The role of neutron excitations across shell gaps and the evolution proton-neutron interaction can be studied in these exotic nuclei. In particular, magic nuclei are key players for the mapping of the single-particle degrees of freedom around closed cores. A special region of interest is found around the doubly-magic 78 28Ni50. In addition, gross properties of these nuclei play a role in the astrophysical rapid neutron capture process. Nuclei in the vicinity of 78Ni have motivated recent experimental and theoretical studies, aimed at the understanding of the nuclear structure in this region with a large neutron excess. In this thesis we investigate the nuclear structure of 81;80Ga, 81Ge and 81As, populated in the decay chain of 81Zn, which was produced at ISOLDE, CERN in the framework of a systematic fast-timing investigation of neutron-rich nuclei populated in the decay of Zn. The selectivity and efficiency of the production of Zn ion beams had been previously optimized in order to guarantee the most pure beam of 77{u100000}82Zn nuclei. The estimated yield of 81Zn was 600 ions/ C giving an average activity of particles during the experiment of about 10000 counts per second. The experimental setup included two HPGe detectors, two LaBr3(Ce) detectors and a NE111A plastic scintillator for particle detection. Coincidences with the detector were used for -ray background suppression, and - coincidences between the HPGe detectors to determine the level schemes. For half-life measurements the combination of LaBr3(Ce) scintillator crystals and Time-to- Amplitude Converters was employed. The signals from the detectors were processed by a digital data acquisition (DAQ) system composed by four Pixie-4 Digital Gamma Finder cards, specially designed for -ray spectroscopy which was used for decay level schemes and the Advanced Time Delayed (“fast-timing“) (t) method employed to measure the excited level lifetimes. From the structural point of view, the isotopes under study are relatively simple systems with a few particles and/or holes outside the doubly-magic core, and thus can be treated rather successfully within the nuclear shell model...