The role of the neutron-proton asymmetry (isospin) in the de-excitation of excited nuclei is investigated by studying the isospin dependence of the Ar+Ni fusion-evaporation cross sections. Compound nuclei of Pd, with mass number varying from 92 (close to the limit of stability for proton emission) to 104 (stable), are produced with the same excitation energy (~3 MeV/nucleon), impinging stable and radioactive Ar beams with energies around 13 MeV/nucleon on to isotopically enriched Ni targets. The de-excitation products are collected by the VAMOS magnetic spectrometer and the 4pi charged particle array INDRA. The study shows a decrease of the Ar+Ni fusion-evaporation cross section as the isospin of the system decreases, suggesting that the deexcitation of excited Pd nuclei is influenced by their neutron-proton asymmetry. Also, a larger decrease is observed for the N = Z 92Pd nucleus, explained as the opening of a new de-excitation channel (multifragmentation).

Precision measurements of superallowed Fermi β-decay allow for stringent tests of the magnitude of isospin-symmetry-breaking effects in nuclei, the validity of the conserved vector current hypothesis, and the unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) quark-mixing matrix. A high-precision measurement of the branching ratio for the superallowed β+ decay of 74Rb has been performed at the Isotope Separator and ACcelerator (ISAC) facility at TRIUMF. The 8π spectrometer, an array of 20 HPGe detectors, was used to detect γ-rays emitted following the Gamow-Teller and non-analogue Fermi β-decays of 74Rb. PACES, an array of 5 Si(Li) detectors, was used to detect emitted conversion electrons, while half of SCEPTAR, a close-packed array of 10 plastic scintillators, was used to detect emitted β particles. In this experiment, 23 excited states were identified in 74Kr which were populated following the β-decay of 74Rb. A total of 58 γ-rays were identified following the 8.241(4)x108 detected β-particles. An observed non-superallowed branching ratio of 0.396(7)% was determined from the intensity of the identified γ-rays, while the unobserved non-superallowed intensity was calculated to be 0.05(5)%, leading to a superallowed branching ratio of 99.55(5)%. The superallowed branching ratio is now the most precise experimental quantity in the determination of the superallowed ft-value of 74Rb. Combining the half-life and Q-value with the superallowed branching ratio measured in this work leads to a superallowed ft-value of 3082.6(66) s. Finally, comparisons between the superallowed ft-value, the world average Ft-value, and the non-analogue Fermi branching ratio are made to provide future guidance in the refinement of the theoretical models required to describe the crucial isospin-symmetry-breaking term in superallowed β-decay.

As part of an ongoing program to study fundamental symmetries in nuclear physics, a thorough investigation into shell-model isospin-symmetry-breaking (ISB) calculation theory has been conducted using direct reactions to observe detailed nuclear-structure information. The work presented in this Thesis focuses on the 62Ga superallowed beta-decay system, and consists of two primary experiments; 1) A 64Zn(d,t)63Zn single-neutron transfer reaction, aimed at observing spectroscopic strengths to help guide calculation model-space truncations for the beta-decay wave function radial-overlap component of ISB, and 2) A two-neutron 64Zn(p,t)62Zn transfer to search for excited 0+ states in the daughter nucleus of 62Ga. The experiments were performed at the Maier-Leibnitz-Laboratory, on the joint campuses of the Ludwig-Maximilians Universitat and the Technische Universitat Munchen, in Garching, Germany. In total, 162 states in 63Zn were populated from the 64Zn(d,t) reaction, up to an excitation energy of 4.8 MeV, including the observation of 125 new levels, and unique spin/parity assignments for 92 states. As a result, this work provides the most complete picture for low-spin states in 63Zn to date. A comparison of the extracted S values to the predicted shell-model spectroscopic factors shows an overall over-prediction of strength for the 2p3/2 orbital, and a large disagreement for the 1f7/2 orbital above ~3.5 MeV. No significant 1g9/2 strength was observed, leading to the conclusion that the importance of the 1g9/2 orbital for ISB is small. Additionally, 67 states were observed in 62Zn using the two-neutron pickup mechanism, including the observation of five 0+ states. More than 99% of the total 0+ (p,t) cross-section is observed in the ground-state reaction channel, implying a nearly maximal overlap of the wave functions with the two-nucleon transfer operator. The dominance of the ground-state-to-ground-state (p,t) cross section is strikingly similar to the dominance of the superallowed Fermi beta-decay between isobaric-analogue 0+ states. This suggests that the population of excited 0+ states in the (p,t) reaction may reflect the population in the Fermi decay process, and can be used to guide future experimental and theoretical work. Further discussion of these results as they relate to the ISB correction calculations, and the implications for future theoretical work are presented in this Thesis. / This work was supported in part by the Natural Sciences and Engineering Research Council of Canada, the Ontario Ministry of Economic Development and Innovation, the DFG Cluster of Excellence `Origin and Structure of the Universe', and NSF grant PHY-1068217.

In this manuscript, some relations between theoretical nuclear physics and compact stars, which are known to be excellent tools to test matter under extreme conditions, are studied. Most of these links are performed within theoretical modelling which are used to describe both nuclei and nuclear systems in astrophysics. Self-consistent approaches unifying the description of isolated nuclei, dilute nuclei in a gas of light particles, and uniform matter, are presented in this manuscript and employed to understand the physics of compact stars. The manuscript is organized as follow: The first chapter is a general introduction to impact stars and supernovae physics, as well as to nuclear physics. In the second chapter, various aspects of the modeling of the in-medium nucleon-nucleon interaction are presented, such as, extension of the Skyrme interaction in the spin and spin-isospin channels, the properties of the V(low k) interaction and the low-density properties of nuclear matter. In the third chapter, the superfluid properties of dense matter are investigated, either through an iso-vector pairing interaction design to reproduce microscopic calculations in nuclear matter, or through the impact of superfluidity on derivatives of the EOS, such as the incompressibility and the symmetry energy, and finally, is presented the use of pairing vibration to study the properties of pairing. The questions of the in-medium effective mass and its impact for the dynamics of core-collapse supernovae, and the level density in nuclei are presented in the chapter 4. The microscopic modelling of the crust of neutron stars, as derived from band theory, and including superfluidity, is shown in chapter 5. In chapter 6, some links between the properties of nuclei, and neutron stars are presented: the properties of overflowing nuclei at the neutron drip, the correlation between the curst-core properties and nuclear empirical quantities, and the stiffness of the nuclear EOS, are shown. Finally, conclusions are presented in chapter 7.

L’algorithme covariant de van Holten, servant à construire des quantités conservées, est présenté avec une attention particulière portée sur les vecteurs de type Runge-Lenz. La dynamique classique des particules portant des charges isospins est passée en revue. Plusieurs applications physiques sont considérées. Des champs de type monopôles non-Abéliens,générés par des mouvements nucléaires dans les molécules diatomiques, introduites parMoody, Shapere et Wilczek, sont étudiées. Dans le cas des espaces courbes, le formalisme de van Holten permet de décrire la symétrie dynamique des monopôles Kaluza-Klein généralisés. La procédure est étendue à la supersymétrie et appliquée aux monopôles supersymétriques.Une autre application, concernant l’oscillateur non-commutatif en dimension trois, est également traitée. / Van Holten’s covariant algorithm for deriving conserved quantities is presented, with particular attention paid to Runge-Lenz-type vectors. The classical dynamics of isospin-carrying particles is reviewed. Physical applications including non-Abelian monopole-type systems in diatoms, introduced by Moody, Shapere and Wilczek, are considered. Applied to curved space, the formalism of van Holten allows us to describe the dynamical symmetries of generalized Kaluza-Klein monopoles. The framework is extended to supersymmetry and applied to the SUSY of the monopoles. Yet another application concerns the three-dimensional non-commutative oscillator.

Dans ce travail nous étudions les collisions 40,48 Ca + 40,48 Ca à E = 35 AMeV , mesurées au GANIL avec le couplage unique du spectromètre VAMOS et du multi-détecteur INDRA. Lors de telles collisions les modèles dynamiques prédisent la formation d’un col à basse densité entre deux fragments chauds cinématiquement proches du projectile et de la cible. L’identification isotopique du projectile désexcité (PLF) apportée par VAMOS, et la topologie des espèces détectées en coïncidence dans INDRA, montrent que l’ évolution du rapport N/Z des produits est influencée par le N/Z du système (projectile et cible). Les multiplicités moyennes des particules légères chargées (LCP, Z ≤ 2) suivent en particulier une hiérarchie selon le N/Z du système, et celles des deutons et particules alphas semblent refléter une production dynamique. Une étude des rapports isotopiques a ensuite mis en exergue les mécanismes de transport de l’isospin : la migration et la diffusion de l’isospin, tous deux liés au terme d’ énergie de symétrie de l’ équation d’ état nucléaire. Un objectif de ce travail a été notamment de contraindre les modèles théoriques grâce à l’expérience. Nous avons ainsi appliqué une étude comparative entre les données, le modèle géométrique ELIE et le modèle de transport AMD, désexcités par le code GEMINI++ et filtrés. Cette étude a mis en exergue que le modèle AMD avec un potentiel effectif Gogny asysoft reproduit mieux l’ évolution expérimentale du N/Z du PLF et la hiérarchie des multiplicités des LCP. Enfin nous avons observé que les rapports isotopiques issus des modèles ne reproduisent pas d’enrichissement en neutrons à la mi-rapidité contrairement à l’expérience. / In this work we study the 40,48 Ca+ 40,48 Ca collisions at E = 35 AM eV , measured at GANIL with the coupling of the large acceptance spectrometer VAMOS and the multi-detector array INDRA. During such collisions transport models predict the formation of a low-density neckbetween two hot fragments kinematicaly close to the projectile and the target. The isotopic identification of the projectile-like fragment (PLF) provided by VAMOS, coupled to the topology of the light-charged particles (LCP) detected in coincidence with INDRA, show that the N/Z ratio of the products is influenced by the N/Z of the system (projectile and target). The mean multiplicities associated to the LCP follow a hierarchy according to the system, and the one associated to deuterons and α particles may well reflect a dynamical production. A studyof the isotopic ratios have highlighted isospin transport mechanisms : the isospin drift and the isospin diffusion, both linked to the symmetry energy term of the nuclear equation of state. A goal of this work was also to constrain theoretical models using experiment. We have thenapplied a systematic study to compare data with the geometrical model elie and the transport model amd, both filtered, and using gemini++ as after-burner. This study have highlighted that the amd model with an asysoft equation of state better fits the experimental evolutionof the N/Z of the PLF and also the LCP mean multiplicites shapes. Finally we have observed that the isotopic ratios don’t reproduce the neutron-enrichment of the mid-rapidity observed in the data.

No description available.

L'étude des effets isotopiques dans le processus de la multifragmentation du projectile spectateur a été effectuée en utilisant le spectromètre ALADiN auprès de l'accélérateur GSI à Darmstadt. Des réactions aux énergies relativistes avec des faisceaux stables d'197Au et 124Sn et des faisceaux radioactifs de 124La et 107Sn ont été utilisés pour couvrir une large gamme en masse et en N/Z. La mesure du vecteur moment et l'identification des fragments du projectile ayant une charge Z>1 entrant dans l'acceptance de l'aimant ALADiN ont été obtenues avec une grande efficacité et résolution en utilisant le dispositif ALADiN amélioré en association avec le détecteur de neutrons LAND. L'étude des propriétés globales de la multifragmentation a montrée une dépendance en N/Z en accord avec les prédictions du modèle statistique de la multifragmentation. L'effet pair-impair dans la multifragmentation du projectile spectateur a été investigé pour pouvoir trouver une interprétation à sa manifestation à hautes énergies d'excitation. Un accord qualitatif a été obtenu pour les mesures de la températures avec les précédentes données et les prédictions théoriques.

Lors de réactions nucléaires dissipatives, un transfert important d'énergie se produit entre le projectile et la cible. Une partie de l'énergie mécanique initiale est emmagasinée sous forme d'énergie thermique dans les noyaux en interaction. Afin de suivre l'évolution de leur comportement lorsque cette énergie augmente, deux techniques de calorimétrie ont été utilisées : l'une dite " calorimétrie 3D " validée et optimisée au cours de cette thèse ; l'autre dite " calorimétrie standard ", déjà très utilisée par la communauté scientifique. Celles-ci ont permis de reconstruire les caractéristiques de Quasi-Projectiles chauds, produits lors de réactions entre systèmes symétriques ou quasi-symétriques. Les avantages et les inconvénients de chacune d'elles ont été étudiés grâce à deux générateurs d'événements, HIPSE et ELIE, modélisant les processus physiques intervenant lors de ces collisions mais qui diffèrent par le scénario de formation du noyau chaud. Cette étude systématique a permis de déterminer pour quelle température et quelle énergie d'excitation par nucléon, des noyaux de masse intermédiaire passent d'un état de liquide nucléaire chaud à un état de gaz nucléaire. Les informations obtenues par la " calorimétrie 3D " ont permis aussi d'isoler en partie la composante dite de prééquilibre. Ce résultat a été confirmé expérimentalement par une nouvelle utilisation du degré de liberté d'isospin (rapport neutron/proton), comme 'marqueur' dans l'espace des vitesses.

Title: Construction of pseudoscalar meson amplitudes in chiral perturbation theory using a dispersive approach Author: Martin Zdráhal Department: Institute of Particle and Nuclear Physics, Faculty of Mathematics and Physics, Charles University in Prague Supervisor: RNDr. Jiří Novotný, CSc. Abstract: We have developed a method enabling a construction of two-loop 2 → 2 scatter- ing amplitudes of pseudoscalar mesons based on the dispersion and the unitarity relations. This method is illustrated on the construction of the amplitudes of all such processes in chiral perturbation theory in isospin limit taking into account strong interactions only. Then it was used for the construction of ππ scattering amplitudes and of K → 3π and η → 3π decay amplitudes including isospin breaking effects induced by different masses of the particles belonging to the same isomultiplet. These parametrizations are prepared for various phenomenological analyses of the ππ scattering lengths and of the isospin breaking effects, both of which could pro- vide us important information for the understanding of quantum chromody- namics at low energies. Finally, we have performed the phenomenological study of η → 3π decay and obtained a value of the quark mass ratio 1/R = (md − mu)/(ms − ˆm). Our conservative estimate is R = 39.6+2.5 −5.1....