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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Coulomb excitation of 66ge

Abrahams, Kenzo January 2021 (has links)
Philosophiae Doctor - PhD / The Coulomb excitation of 66Ge has been performed for the rst time using \safe" bombarding energies at the HIE-ISOLDE facility at CERN in July 2017. A particle- coincidence experiment using the MINIBALL array and double-sided silicon detectors has allowed the determination of transitional and diagonal matrix elements in 66Ge, yielding new measurements of the reduced transition probability connecting the ground state, 0+1 , and the rst excited state, 2+1 , or B(E2; 2+1 ! 0+1 ) value, and the spectroscopic quadrupole moment of the 2+1 state, QS (2+1 ). A relatively large B(E2) = 29:4(30) W.u. has been extracted using beam-gated data at forward angles { less sensitive to secondorder e ects { as compared with the adopted value of 16:9(7) W.u., but in closer agreement with modern large-scale shell-model calculations using a variety of e ective interactions and beyond-mean eld calculations presented in the current work. / 2022
2

Nuclear Structure Relevant to Double-beta Decay: Studies of ⁷⁶Ge and ⁷⁶Se using Inelastic Neutron Scattering

Crider, Benjamin P 01 January 2014 (has links)
While neutrino oscillations indicate that neutrino flavors mix and that neutrinos have mass, they do not supply information on the absolute mass scale of the three flavors of neutrinos. Currently, the only viable way to determine this mass scale is through the observation of the theoretically predicted process of neutrinoless double-beta decay (0νββ). This yet-to-be-observed decay process is speculated to occur in a handful of nuclei and has predicted half-lives greater than 10²⁵ years. Observation of 0νββ is the goal of several large-scale, multinational efforts and consists of detecting a sharp peak in the summed β energies at the Q-value of the reaction. An exceptional candidate for the observation of 0νββ is ⁷⁶Ge, which offers an excellent combination of capabilities and sensitivities, and two such collaborations, MAJORANA and GERDA, propose tonne-scale experiments that have already begun initial phases using a fraction of the material. The absolute scale of the neutrino masses hinges on a matrix element, which depends on the ground-state wave functions for both the parent (⁷⁶Ge) and daughter (⁷⁶Se) nuclei in the 0νββ decay and can only be calculated from nuclear structure models. Efforts to provide information on the applicability of these models have been undertaken at the University of Kentucky Accelerator Laboratory using gamma-ray spectroscopy following inelastic scattering reactions with monoenergetic, accelerator-produced fast neutrons. Information on new energy levels and transitions, spin and parity assignments, lifetimes, multipole mixing ratios, and transition probabilities have been determined for ⁷⁶Se, the daughter of ⁷⁶Ge 0νββ, up to 3.0 MeV. Additionally, inaccuracies in the accepted level schemes have been addressed. Observation of 0νββ requires precise knowledge of potential contributors to background within the region of interest, i.e., approximately 2039 keV for ⁷⁶Ge. In addition to backgrounds resulting from surrounding materials in the experimental setup, ⁷⁶Ge has a previously observed 3952-keV level with a de-exciting 2040-keV γ ray. This γ ray constitutes a potential background for 0νββ searches, if this level is excited. The cross sections for this level and, subsequently, for the 2040-keV γ ray has been determined in the range from 4 to 5 MeV.
3

Étude expérimentale et théorique de la structure nucléaire des isotopes de sélénium riches en neutrons. / Experimental and theoretical study of the nuclear structure of the neutron-rich selenium isotopes.

Gratchev, Ivan 13 November 2017 (has links)
Le présent manuscrit de thèse regroupe les études par spectroscopie γ des noyaux 84−88Se produits par une réaction de fission induite par neutrons thermiques, sur une cible de 235U. Cette expérience a été réalisée à l’Institut Laue-Langevin à Grenoble après du multi-détecteurs EXILL. Les données brutes recueillies par EXILL ont été traitées et analysées afin de déterminer la structure des noyaux étudiés. Grâce à cette étude spectroscopique détaillée, un premier schéma de niveaux a été établi pour la première fois au 88Se et de nouveaux états excités ont été assignées à d’autre isotopes de sélénium (84-87Se). De plus, l’analyse de la corrélations angulaires a été faite pour confirmer l’assignation de spins des premières états excités. Des calculs théoriques utilisant le modèle en couches (SM), le modèle collectif algébrique (ACM) et le modèle quasiparticule plus phonon (QPM), ont été effectués pour interpréter la structure nucléaire et la forme du noyau d’intérêt 88Se. Selon ces modèles, le noyau 88Se est γ-instable et peut être interprété comme un noyau transitoire et sa structure nucléaire du 88Se a été bien reproduite par le modèle en couches et le modèle ACM. Les calculs du modèle QPM indiquent que le degré de collectivité de l’état 22+ du 88Se est faible parce que une composante neutronique reste dominante dans la structure de la bande γ. / The present thesis manuscript includes the nuclear spectroscopy studies of 84−88Se. A more favourable fission reaction for their study is 235U(nth, f). The measurement was performed at the PF1B cold-neutron beam facility of the Institut Laue-Langevin (ILL), Grenoble. The fission reaction has been used in conjunction with the EXILL Ge array to study excited states in the neutron-rich Se nuclei. Thanks to this spectroscopic study, a first level scheme of 88Se was established and new excited states were assigned to other selenium isotopes. Furthermore, the angular correlation studies were carried out to confirm the spin assignment of the first excited states in the 84-88Se nuclei. The theoretical calculations using the shell model (SM), the algebraic collective model (ACM) and the quasiparticle plus phonon model (QPM) were performed in order to interpret the nuclear structure and the shape of the nucleus of interest 88Se. According to these models, the nucleus 88Se is γ-unstable and can be interpreted as a transitional nucleus. The shell-model calculations using a 78Ni core and the ACM calculations reproduce the decay scheme of 88Se well. The QPM calculations show that the collectivity of second state 2+2 of 88Se is weak and that this state contains a strong quasiparticle component.
4

Recherche de déformation dans des noyaux riches en neutrons / Search for deformation in neutron rich nuclei

Mancuso, Clément 04 July 2016 (has links)
Actuellement, le noyau de l'atome sert dans diverses utilisations courantes. Pourtant, notre compréhension que de cet objet n'est pas complète. C'est pourquoi la recherche nucléaire est nécessaire. Parmi cet ensemble vaste, ce manuscrit s'intéresse à l'étude des changements de forme dans les isotopes riches en neutrons des séries Ru et Sr. Le sujet est d'abord cerné dans un chapitre de concepts théoriques de la physique nucléaire. Un second chapitre décrit l'expérience permettant de produire les isotopes d'intérêt. Cette expérience de spectroscopie gamma est réalisée avec un multidétecteur HPGe composé à partir d'EXOGAM et complété de cristaux GASP et LOHENGRIN. Cette expérience consiste en la fission du 241Pu induite par neutrons froids fournis par le réacteur de l'Institut Laue Langevin. Elle fait partie de la campagne EXILL. Le deuxième chapitre traite également de la pré-analyse des données. Après avoir montré les effets d'une pré-sélection des événements en multiplicité, les résultats obtenus concernant les isotopes 108Ru à 115Ru, et 92Sr à 96Sr sont abordés dans le troisième chapitre. Enfin, le quatrième chapitre replace ces résultats dans des ensembles plus larges des parties riches en neutrons des deux séries. Ces séries sont également replacées dans le contexte de leur région de masse.La région d'intérêt est riche en changement de forme, avec l'enrichissement neutronique ou avec l'excitation des noyaux. Ces changements sont plutôt bien décrits par certains modèles, mais ces derniers peinent encore à en décrire les limites. Leurs déterminations précises est essentielle pour contraindre les modèles / Nowadays, the atomic nucleus is used in a variety of common way. Nevertheless, this object is not fully understood yet. This is why nuclear physics research is still needed. Among the large number of nuclear physics topics, this work is interested in the study of shape changes in neutron rich Ru and Sr isotopes. The subject is figured out in the first chapter, dealing with theoretical concepts about nuclear physics. A second chapter describes the experiment permitting to produce the isotopes of interest. This gamma-ray spectroscopy experiment has been realized with a HPGe multidetector made from EXOGAM and completed by GASP and LOHENGRIN detectors. This experiment consists of the cold neutron, supplied by the reactor of the Institute Laue Langevin, induced fission of 241Pu. This experiment is a part of the EXILL measurement campaign. The second chapter also deals with the data pre-analysis of this experiment. After showing the effects of a multiplicity cut on event preselection, the obtained results concerning 108Ru to 115Ru and 92Sr to 96Sr isotopes are presented on the third chapter. Finally, the fourth chapter puts these results in a wider part of the neutron rich side of both series. These last ones are also placed in their mass region context.The region of interest is rich in shape change, whether with neutronic enrichment or with excitation energy. These changes are rather well described by certain models, but the latter still have difficulty to describe the limits. Their precise determinations by experiment is essential to constrain models

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