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Theses

Fusion et réactions directes autour de la barrière Coulombienne avec le noyau riche en neutrons 8He

Abstract : Radioactive ion beams like 8He, open new possibilities to investigate the influence of new and exotic structures on reaction mechanisms. This thesis presents the first investigations of reactions of the weakly bound, Borromean nucleus, 8He, at energies around the Coulomb barrier. The low intensity of radioactive ion beams ( ˜ 105pps ) necessitated the development of a new sensitive and selective technique for the precise and accurate measurement of fusion cross sections. In the 8He+197Au system, excitation functions for fusion and neutron(s) transfer were measured. In the 8He+65Cu system, differential and integral cross sections for various processes like elastic scattering, neutron transfer and fusion were measured using both, inclusive and exclusive measurements of characteristic γ -rays, charged particles and neutrons. These experimental results combined with coupled reaction channels calculations demonstrated the inter-connectivity among the various reaction processes. The internal structure of 8He influenced the tunneling process and neutron(s) transfer and interestingly, revealed an unexpected behavior within the Helium isotopic chain. Further, a systematic analysis of the known fusion excitation functions showed that the increase in sub-barrier fusion cross sections associated with the internal structure of nuclei, is in fact much larger for “normal” nuclei than for light, weakly-bound “exotic” nuclei.
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Submitted on : Wednesday, October 20, 2010 - 4:33:46 PM
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Antoine Lemasson. Fusion et réactions directes autour de la barrière Coulombienne avec le noyau riche en neutrons 8He. Physique Nucléaire Expérimentale [nucl-ex]. Université de Caen, 2010. Français. ⟨tel-00522577⟩

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