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Etude des liens entre puits superdeformé et puits normalement deformé dans $^{192}$Hg & recherche et développement pour un nouveau concept de détection de photons $\gamma$ : le multidétecteur AGATA

Abstract : The atomic nucleus can adopt a very elongated shape with an axis ratio 2:1 : this is the superdeformation phenomenon. Nowadays more than 300 superdeformed bands have been identified at high spin, but the determination of excitation energies, spins and parities of the associated states have been established for only one tenth of these bands. The former quantities (e*, i, $\pi$) can only be determined via the linking gamma-transitions between the superdeformed (sd) and the normally deformed (nd) states.

Within the framework of this thesis, we have investigated the $^{192}$hg nucleus in order to establish e*, i and $\pi$  this nucleus is predicted to be doubly magic at superdeformation and hence is taken as a reference in the mass a~190 region. The experiment was carried out at Strasbourg using the Euroball IV array and the vivitron accelerator.

The obtained results are not convincing and seem to be at the limit of the performances of Euroball. Next generation of arrays will abandon the Compton-shields and use tracking concept to reconstruct the trajectories of incident photons, and therefore we expect a huge increase of efficiency.

The second part of this ph. D. Was focused on the R&D work for the Agata project. We have performed simulations with the geant4 code and developped tracking methods to reconstruct pair-creation events. The full Agata will be operationnal around 2015 and will enhance by around two orders of magnitude the observational limits.
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Submitted on : Friday, June 22, 2007 - 9:48:36 AM
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Jérôme Roccaz. Etude des liens entre puits superdeformé et puits normalement deformé dans $^{192}$Hg & recherche et développement pour un nouveau concept de détection de photons $\gamma$ : le multidétecteur AGATA. Physique Nucléaire Théorique [nucl-th]. Université Paris Sud - Paris XI, 2006. Français. ⟨tel-00156648⟩

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