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Population et structure des noyaux ²¹⁰Po et ²¹²Po produits par réactions de transfert

Abstract : Several light nuclei, as ¹⁸O, display a ”core+ α” structure. ²¹²Po is the only heavy one where this phenomenon has been highlighted. In this thesis, we combined the measurement of the excitation energy of levels populated via transfer reaction from a ¹² C nucleus on a ²⁰⁸Pb nucleus, and the measurement of the γ decaying of these levels. A first experiment has been performed in inverse kinematic, using the AGATA Germanium array and a thick silicon detector. A second experiment, in direct kinematic has been done at Tokai’s Tandem using a telescope of silicon detectors, 4 HPGe and 4 LaBr₃ crystals. We describe the principle of these detectors, the datareduction up to the kinematical reconstruction, and the simulations used to build the experimental set-up and to validate the data analysis. We have studied 1p, 2p, 2p 1n and α transfer reactions leading to ²⁰⁹Bi, ²¹⁰Po, ²¹¹Po and ²¹²Po at energies around the Coulomb barrier.From the comparison of these reactions channels, we firmly established that the 4 nucleons are transfered simultaneously to produce ²¹²Po. Evolution of the excitation energy with the beam energy has shown that the 212Po states including a strong ”core + α” component lie much preferentially at high excitation energy (E∗ ≥ 3 MeV).Seven new energy levels of ²¹² Po have been discovered, for which spin and parity attributions are proposed. We also measured the partial cross-sections to several levels to characterize their cluster components. We confirmed the large ”core + α” components of the 4⁻₃ and 7⁺₂ and 7+2 states, and the weak ”core + α” components of the 2⁺₁ and 2⁺₂ states.Five new levels of ²¹⁰Po have been discovered. Shell model calculations allowed us to frimly assign spins and parities.
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Etienne Dupont. Population et structure des noyaux ²¹⁰Po et ²¹²Po produits par réactions de transfert. Physique Nucléaire Expérimentale [nucl-ex]. Université Paris-Saclay, 2019. Français. ⟨NNT : 2019SACLS429⟩. ⟨tel-02493224⟩

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