Processus de Fusion-Fission et Spectroscopie Gamma des Produits Binaires dans les Collisions entre Ions Lourds L'egers (40 < ANC < 60)

Abstract : During the work of this Thesis, the significant role of the \underline{Fusion-Fission} \underline{ Asymmetric} mechanism in light heavy ions collisions (A$_{\rm NC} \le$60) has been emphasised. The \underline{Spin Disalignment} in the {\it oblate-oblate} system has supplied evidence \underline{for the first time for the} \underline{Butterfly mode in a resonant-like reaction}. These two aspects, one macroscopic and the other more closely related to microscopic effects are certainly different from a conceptual point of view but are quite complementary for a global understanding of dinuclear systems. \par \hspace*{0.5cm}In the first part, inclusive and exclusive measurements of the $^{35}$Cl $+$ $^{12}$C and $^{35}$Cl $+$ $^{24}$Mg reaction have been performed at 8 MeV/nucleon in the Saclay experiment. These measurements have permitted us to verify the origin of products which have given rise of the asymmetric fusion-fission mechanism and which have demonstrated that the \underline{three-body} process in this energy range is very weak. In the second part the $^{28}$Si $+$ $^{28}$Si reaction has been performed on the resonance energy E$_{lab.}$ = 111.6 MeV at Strasbourg with the Eurogam phase II multi-detector array and VIVITRON accelerator. An angular momentum J$^{\pi}$ = 38$^{+}$ for inelastic and mutual channels of the $^{28}$Si $+$ $^{28}$Si exit channel has been measured and has supplied evidence for a \underline{spin disalignment} which has been interpreted in the framework of a molecular model by \underline{Butterfly motion}. The spectroscopic study of $^{32}$S nucleus, has revealed the occurence of a new $\gamma$-ray transition $0^{+} (8507.8\ keV) \to 2^{+}_{1} (2230.2\ keV) $.
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Rachid Nouicer. Processus de Fusion-Fission et Spectroscopie Gamma des Produits Binaires dans les Collisions entre Ions Lourds L'egers (40 < ANC < 60). Physique Nucléaire Expérimentale [nucl-ex]. Université de Strasbourg, 1997. Français. ⟨tel-00805800⟩

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