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This dissertation reports on new information in the [beta minus] decay of the neutron-rich nucleus 81Zn, which populates states in its daughter nucleus 81Ga. This includes new [gamma]-ray transitions in the daughter nucleus, 81Ga, as well as a [beta]-delayed neutron branching ratio. This isotope was produced at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory through the Isotope Separation Online technique. They are fission fragments from proton-induced fission on a uranium carbide target. These fission fragments are ionized and both mass and isotopically separated before arriving at the Low Energy Radioactive Ion Beam Spectroscopy Station (LeRIBSS). The [gamma]-ray and [beta] electron emissions from the decays are measured and analyzed in this work. A new [beta]-delayed neutron branching ratio is reported for this decay, which is in agreement with recent theoretical values. The core excited states in the daughter nucleus, 81Ga, populated through allowed Gamow-Teller decays are analyzed. A trend in core excited states with other N=50 isotones indicates an increasing gap between a deeply bound neutron hole and the valence neutron above the N=50 gap upon moving towards doubly magic 78Ni. This dissertation also reports on additions to the decay schemes of 79Zn and 80Zn decays. Their decay level schemes have been expanded upon and an improved picture of the total allowed Gamow-Teller decay strength is known from 79Zn to 81Zn. This work presents an improved, albeit still incomplete, picture of the energy of states populated through Gamow-Teller decays from below to above the N=50 shell gap in zinc isotopes.

Cette thèse porte sur l'étude des probabilités d'émission gamma et de fission du noyau composé 240Pu. Les probabilités sont obtenues en utilisant la méthode de substitution qui vise, par le choix approprié de réactions nucléaires, à former un noyau composé identique en masse et en énergie d'excitation à celui formé dans une réaction de capture neutronique. Le but est de combler le manque de données nucléaires, dans les cas de cibles très radioactives, pour la physique des réacteurs et l'astrophysique. En effet, dès lors que les expériences de réactions en neutron induit sur ces noyaux ne sont pas réalisables, les capacités prédictives des modèles de réactions sont mises en question car elles aussi sont difficilement ajustables avec trop peu de données. Les probabilités d'émission gamma ou de fission du noyau composé formé dans ces réactions de substitution peuvent servir à améliorer significativement les prédictions. Pour cela, l'élément crucial est de comprendre les différences entre les processus de formation et de désexcitation des noyaux formés dans ces réactions et dans celles induites par neutron.Depuis plusieurs années, une collaboration entre les laboratoires de physique nucléaire CENBG et CEA/DAM/DIF, fournit des éléments pour la compréhension de ces processus. Notamment en s'intéressant à la distribution en spin du noyau composé dans les réactions de substitution, elle a pu montrer qu'elle était très différente de celle induite par neutron et jouait un rôle important dans la compétition entre l'émission gamma et neutrons. Cependant, son rôle moindre dans la fission était plus ambigu. Pour essayer de comprendre cela, on a étudié le 240Pu, un noyau pair-pair, en utilisant un dispositif expérimental développé par la collaboration pour mesurer simultanément la probabilité de décroissance gamma et fission.Avec ce dispositif une expérience a été réalisée en 2017 au tandem de l'IPN d'Orsay, où on a fait interagir un faisceau de particules alpha, à 30MeV d'énergie, avec la cible de 240Pu. Les particules alpha diffusées inélastiquement, ou éjectiles, étaient détectés par des télescopes, permettant d’identifier le noyau décroissant et de déterminer son énergie d'excitation. Les voies de décroissance du noyau composé formé sont alors identifiées, en coïncidence, par détection des gammas et des fragments de fission. Les probabilités d’émission gamma et de fission sont obtenues en effectuant le rapport du nombre d’éjectiles détectées par le nombre de coïncidences mesurées corrigé des efficacités.Pour interprétation de ces données inédites, nous avons procédé par étapes. Dans un premier temps nous avons ajusté les paramètres du modèle réaction (densités de niveaux, hauteur des barrières de fission, etc.) du noyau composé 240Pu, en se basant sur les données neutroniques de la réaction n+239Pu. Ensuite nous avons calculé les rapports d'embranchement G du noyau composé, soit la probabilité du noyau de décroître par une certaine voie pour un spin, une parité et une énergie d'excitation donnés. Finalement avec M. Dupuis (CEA/DAM/DIF), un calcul de réaction pour prédire la distribution de spin du 240Pu lors de la réaction de diffusion inélastique a été réalisé pour la première fois à l'aide du potentiel optique JLM associé à la méthode QRPA pour décrire les excitations du noyau.La combinaison des distributions de spin et parité calculées et les rapports G, a permis d'extraire des probabilités de décroissance calculées. La comparaison avec nos probabilités mesurées montre un très bon accord, indiquant une bonne compréhension des mécanismes de réaction alpha,alpha'. Une utilisation dans le futur de ce type de réaction pourra apporter des informations supplémentaires à un processus d'évaluation des sections efficaces de capture radiative et de fission pour des noyaux plus exotiques. / This PhD thesis revolves around the study the gamma-decay and fission probabilities of the compound nucleus (CN) 240Pu. These probabilities are obtained by using the surrogate reaction method, which, through charged particle reactions, aims to produce the same compound nucleus as the one that would be formed through a neutron induced reaction, or desired reaction. The objective is to cover the shortage of nuclear data, in cases in which the targets are too radioactive to be measured directly, for astrophysics and applications. As a matter of fact, if the measurement of the desired reaction is not possible, the reaction models reliance is compromised as their parameters cannot be adjusted. In this cases the gamma-decay and fission probabilities of the CN formed through the surrogate reaction, can help to improve the models. To this end, it is crucial to understand the difference between the formation and decay processes in the compound nuclei formed through a surrogate reaction and a neutron induced one.A collaboration between the nuclear physics laboratories, CENBG and CEA/DAM/DIF, is making the state of the art of surrogate reactions advance. In particular giving some insight about the spin distribution of the CN formed with these reactions, which they proved different to that of the nuclei formed through neutron induced reactions and that this played an important role in the competition between gamma-decay and neutron emission. Nevertheless, this does not seem to be the case for fission, whose data are in agreement with neutron induced ones. To better understand this, we have studied 240Pu, an even-even nucleus, using an experimental setup developed by this collaboration to simultaneously measure gamma-decay and fission.With this set-up, we performed an experiment in 2017 at the tandem accelerator at the IPN of Orsay (France). There a 30 MeV alpha particles beam interacted with the 240Pu target. The inelastically scattered alpha particles, ejectiles, were detected by two telescopes, which allow to identify the decaying nucleus and determine its excitation energy. The decay paths of the formed CN were identified, in coincidence with the telescopes, by detecting the gamma-rays and the fission fragments. With this information, the gamma-decay and fission probabilities were obtained by doing the ratio between the number of detected ejectiles and the number of measured coincidences correct by the detection efficiency.To interpret these unique data, we proceeded in three steps. Firstly, we adjusted the reaction model parameters (nuclear level densities, fission barriers, etc.) of the compound nucleus 240Pu with the existing data of the n+239Pu reactions. Then we calculated the branching ratios G of the decaying nucleus, which represent the probability of the nucleus to decay through a certain channel, for a certain excitation energy, spin and parity. Finally, with M. Dupuis (CEA/DAM/DIF), a calculation to predict the spin distribution of the 240Pu formed through the inelastic scattering of alpha particles was done for the first time. The calculation combined a JLM optical potential with the states of the nucleus generated with a QRPA approach.The spin distribution obtained with this calculation was combined with the calculated branching ratios G to calculate the decay probabilities. The comparison of this calculation to our measured probabilities shows a good agreement, which indicates a good a understanding of the reaction mechanism alpha,alpha'. Using this type of inelastic reaction in the future, could provide additional information about the radiative capture and fission cross sections of more exotic nuclei.

The directional correlation of the 346-136 Kev gamma-gamma cascade in Ta¹⁸¹ was measured using the delayed coincidence method with a source of Hf¹⁸¹ in 27 N HF. The contributions to the composite delayed coincidence spectrum of the interfering 133-482 Kev and 133 - 346 Kev cascades were removed by the subtraction from this spectrum of appropriate 133-482 Kev pure delayed coincidence data. The extracted 346 -136 Kev coincidence data then yielded the correlation coefficients A₂₂ = o.190 土0.011 and A₄₄. = -0.025 土O. 024 that are consistent with the established spin sequence 5/ 2(E2)9 / 2(Ml +E2)7 / 2 and with an admixture of 16.20/0土1. 2% E2 radiation in the 136 Kev mixed transition. The results of the experiment are in excellent agreement with those obtained from conversion electron measurements and resolve the discrepancy apparent in earlier work on the 346-136 Kev cascade

The investigation of isomeric states in neutron-rich nuclei provides useful insights into the underlying nuclear configurations, and understanding their occurrence along an isotopic chain can inform about shell evolution. Recent studies on neutron-rich Si isotopes near the magic number N = 20 and approaching N = 28 have revealed the presence of low-lying states with intruder configurations, resulting from multiple-particle, multiple-hole excitations across closed shell gaps. The characterization of these states involves measuring their half-lives and transition probabilities. In this study, a new low-energy (7/2−1) isomer at 68 keV in 37Si was accessed via beta decay and characterized. To achieve this, radioactive 37Al and 38Al ions were produced through the projectile fragmentation reaction of a 48Ca beam and implanted into a CeBr3 detector, leading to the population of states in 37Si. The 68-keV isomer was directly populated in the beta-delayed one neutron emission decay of implanted 38Al ions. Ancillary detector arrays comprising HPGe and LaBr3(Ce) detectors were employed for the detection of beta-delayed gamma rays. The choice of detectors was driven by their excellent energy and timing resolutions, respectively. The beta-gamma timing method was utilized to measure the half-life of the new isomeric state in 37Si. This dissertation also discusses other timing techniques employed to search for and characterize isomeric states following beta decay of implanted ions. Notably, the half-life of the newly observed (7/2−1) isomeric state in 37Si was measured to be 9.1(7) ns. The half-life of the previously observed closely-lying (3/2−1) state at 156 keV was determined to be 3.20(4) ns, consistent with previously reported values. Reduced ground-state transition probabilities associated with the gamma-ray decay from these excited states were in agreement with results obtained from shell model calculations. In addition to the investigation of isomeric states in 37Si, isomeric 0+ states in 34Si and 32Mg nuclei belonging to the N = 20 “island of inversion” were characterized and searched for, respectively. The isomeric 0+ state in 34Si was populated following the beta decay of implanted 34Mg ions and its 34Al daughter nucleus. Similarly, the 0+ state in 32Mg was searched for via the beta-delayed one neutron emission decay of implanted 33Na ions.

Made available in DSpace on 2014-10-09T12:41:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:33Z (GMT). No. of bitstreams: 0 / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Made available in DSpace on 2014-10-09T12:41:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:04:33Z (GMT). No. of bitstreams: 0 / O Laboratório de Metrologia Nuclear (LMN) do Instituto de Pesquisas Energéticas e Nucleares (IPEN) desenvolveu recentemente o Sistema de Coincidência por Software (SCS), para a digitalização e registro dos sinais de seus sistemas de coincidências 4πβ-γ utilizados na padronização de radionuclídeos. O sistema SCS possui quatro entradas analógicas independentes que possibilitam o registro simultâneo dos sinais de até quatro detectores (vias β e γ). A análise dos dados é realizada a posteriori, por software, incluindo discriminação de amplitudes, simulação do tempo-morto da medida e definição do tempo de resolução de coincidências. O software então instalado junto ao SCS estabeleceu a metodologia básica de análise, aplicável a radionuclídeos com decaimento simples, como o 60Co. O presente trabalho amplia a metodologia de análise de dados obtidos com o SCS, de modo a possibilitar o uso de detectores com alta resolução em energia (HPGe), para padronização de radionuclídeos com decaimentos mais complexos, com diferentes ramos de decaimento ou com transições metaestáveis. A expansão metodológica tem suporte na elaboração do programa de análise denominado Coincidence Analyzing Task (CAT). A seção de aplicação inclui as padronizações do 152Eu (diferentes ramos de decaimento) e do 67Ga (nível metaestável). A padronização do 152Eu utilizou uma amostra de uma comparação internacional promovida pelo BIPM (Bureau International des Poids et Mesures), podendo-se comparar a atividade obtida com o valores de laboratórios mundialmente reconhecidos, de modo a avaliar e validar a metodologia desenvolvida. Para o 67Ga, foram obtidas: a meia-vida do nível metaestável de 93 keV, por três diferentes técnicas de análise do conjunto de dados (βpronto-γatrasado-HPGe, βpronto-γatrasado-NaI e βpronto- βatrasado); as atividades de cinco amostras, normalizadas por Monte Carlo e as probabilidades de emissão gama por decaimento, para nove transições. / Tese (Doutoramento) / IPEN/T / Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Les sections efficaces induites par neutrons des noyaux de courte durée de vie jouent un rôle important dans des domaines variés parmi la physique fondamentale, l'astrophysique ou l'énergie nucléaire. Malheureusement de nombreuses contraintes liées à la radiotoxicité des cibles rendent la mesure de ces sections efficaces souvent très difficiles. La méthode de substitution est une technique de mesure indirecte de sections efficaces neutroniques de noyaux radioactifs qui à l'avantage de s'affranchir de ces contraintes. Pour la première fois dans ce type d'expérience,les probabilités de fission et d'émission gamma sont mesurées simultanément, pour les actinides236U, 238U, 237Np et 238Np dans le but d'étudier la validité de la méthode. Une des difficultés provient de la soustraction des gammas des fragments de fission et cette mesure constitue en cela un véritable défi. Cette expérience de mesure simultanée a été effectuée au cyclotron d'Oslo.A une énergie d'excitation fixée du noyau formé, les résultats montrent que les probabilités de fission de substitution sont en bon accord avec celles induites par neutron alors que les probabilités d'émission gamma mesurées sont plusieurs fois plus élevées. Ces écarts sont liés à la différence distribution spin peuplée par le noyau entre les deux méthodes. Des calculs de modèles statistiques avec des paramètres standards n'ont pas permis de reproduire cette insensibilité de la probabilité de fission vis à vis du spin du noyau. La reproduction des observations expérimentales devient possible en considérant un moment d'inertie du noyau fissionnant qui augmente plus rapidement avec la déformation du noyau que ne le préconisent les paramètres standards. De nouveaux efforts théoriques sont à fournir pour améliorer la compréhension de nos résultats. / Neutron-induced cross sections of short-lived nuclei are important in various fields such as fundamental physics, astrophysics or nuclear energy. However, these cross sections are often extremely difficult to measure due to high radioactivity of the targets involved. The surrogate-reaction method is an indirect way to determine neutron-induced cross sections of short-lived nuclei. In order to study the validity of the method, we have measured for the very first time in a surrogate-reaction experiment simultaneously fission and gamma-decay probabilities for the actinides 236U, 238U, 237Np and 238Np. This is challenging because one has to remove the gamma rays emitted by the fission fragments. The measurement was performed at the Oslocyclotron.Our results show that for a given excitation energy, our gamma-decay probabilities are several times higher than neutron-induced probabilities, which can be attributed to differences in spin distribution between the two types of reactions. On the other hand, our fission probabilities are in good agreement with neutron-induced data. Statistical-model calculations applied with standardparameters cannot reproduce the weak spin sensibility to variations of the angular momentum observed for the fission probabilities. However, it is possible to reproduce the experimental observations by considering a stronger increase of the moment of inertia of the fissionning nucleus with deformation. Further theoretical efforts are needed to improve the understanding of our results

Title: Electroweak processes in the framework of effective field theory Author: Petr Soukup Department: Institute of Particle and Nuclear Physics Supervisor: RNDr. Karol Kampf, Ph.D. Supervisor's e-mail address: kampf@troja.mff.cuni.cz Abstract: In this thesis, we study electroweak processes within the framework of ef- fective field theory employing the approach of effective Lagrangians. We mainly focus on the decay process H → γγ. A complete set of SU(2) × U(1) invariant dimension- six operators is utilized. We present a brief introduction to GWS Standard model and dimension-six effective operators. One-loop Standard model contribution to the process of H → γγ is then evaluated, followed by calculation of tree-level and one-loop level dimension-six operators contribution to the same process. We then present a brief ge- neral summary of renormalization procedure in quantum field theory. Renormalization of performed calculations is implemented, and possible issues that may arise during renormalization of such non-renormalizable theory are also discussed. In the end, we discuss the obtained results, mainly the dependence of H → γγ decay rate on effective theory's free parameters and the scale of the new physics Λ. Focus is made on possible deviations from Standard model results. The results are plotted in charts....