Thèse soutenue

Etude de la structure nucléaire loin de la stabilité : Excitation Coulombienne des isotopes de Rb riche en neutrons autour de N=60 ; Production de faisceaux au spin nucléaire polarisé via la technique des « Feuilles Orientées »
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Auteur / Autrice : Christophe Sotty
Direction : Georgi Georgiev
Type : Thèse de doctorat
Discipline(s) : Physique nucléaire
Date : Soutenance le 22/03/2013
Etablissement(s) : Paris 11
Ecole(s) doctorale(s) : Ecole doctorale Modélisation et Instrumentation en Physique, Energie, Géosciences et Environnement (Orsay, Essonne ; 2010-2015)
Partenaire(s) de recherche : Laboratoire : Centre de sciences nucléaires et de sciences de la matière (Orsay, Essonne ; 1998-2019) - Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse
Jury : Président / Présidente : Jean-Antoine Scarpaci
Examinateurs / Examinatrices : Georgi Georgiev, Jean-Antoine Scarpaci, Nadine Redon, Andreas Görgen, Barbara Sulignano
Rapporteurs / Rapporteuses : Nadine Redon, Andreas Görgen

Résumé

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The underlying structure in the region A~100, N~60 has been under intensive and extensive investigation, mainly by β-decay and γ-ray spectroscopy from fission processes. Around N~60, by adding just few neutrons, protons a rapid shape change occurs from spherical-like to well deformed g.s. shape. Shape coexistence has been observed in the Sr and Zr nuclei, and is expected to take place in the whole region. The mechanisms involved in the appearance of the deformation is not well understood. The interplay between down-sloping and up-sloping neutron Nilsson orbital is evoked as one of the main reasons for the sudden shape change. However, a clear identification of the active proton and neutron orbitals was still on-going. For that purpose, the neutron rich ⁹³′⁹⁵′⁹⁷′⁹⁹Rb isotopes have been studied by Coulomb excitation at CERN (ISOLDE) using the REX-ISOLDE post-accelerator and the MINIBALL setup. The completely unknown structures of ⁹⁷′⁹⁹Rb have been populated and observed. Prompt γ-ray coincidences of low-lying states have been observed and time correlated to build level schemes. The associated transition strengths have been extracted with the GOSIA code. The observed matrix elements of the electromagnetic operator constituted new inputs of further theoretical calculations giving new insight on the involved orbitals. The sensitivity of such experiment can be increased using nuclear spin polarized RIB. For that purpose the Tilted Foils Technique (TFT) of polarization has been investigated at CERN. A new TFT polarizer with a β-NMR setup have be created and installed after REX-ISOLDE. The uncomplete knowledge of the polarization process associated to the technique needs to be investigated. Conclusive preliminary tests have been performed on ⁸Li in order to determine the potential of the present setup.