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Structure des noyaux de gallium, de germanium et d'arsenic riches en neutrons autour de N=50 et Développement d'une source d'ionisation laser à ALTO

Abstract : In this work of thesis, we study β decays of gallium's nucleus around N=50 and prepare a laser ionization source at ALTO. The region of rich-neutrons nucleus around N=50 is still to study. The knowledge of those nucleus is thick and does not allow to close the discussions about those nucleus. So 79,80,82,83,84,85Ga have been produced at ALTO. A electron-beam (50MeV and 10µA) from a linear accelerator has been send to a target of uranium carbide worn 2000°C. In target, electrons emit bremsstrahlung radiations wich induce the fission of uranium nucleus. The fission-products spread up to surface ionization source wich is at exit of taget to ionize gallium nuclei and produce pure beams of gallium. This system allow us to study β- and β- -n decays of 79,80,82,83,84,85Ga. During this thesis, lasers have been installed and optimized to ionize selectively atoms of copper produced at ALTO. After the optimisation, a test of ionization of stable-copper has been perfomed. This test showed that the laser system ionize copper but the setup has not allowed to mesure the ionization efficiency : the lasers were not stable in position. The data analysis of experiment of β decays of 79,80,82,83,84,85Ga produced new results on decays of 80Ga, 84Ga and 84Ge. The data analysis confirmed the existence of an isomeric state of 80Ga and allowed to measure two different life-time for 80Ga. Furthermore, the analysis gave new indications on the states of 84As. Finally, the comparison between experimental results and theorical calculations confirmed the assignment of spin-parity of the first states 2+ and 4+ but also the triaxial character of 84Ge proposed by Lebois et al.. The second state 2+ of this isotope was also identified. For the states of 84As, the assignment of spins and parities of four states was proposed.
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Submitted on : Friday, September 9, 2011 - 1:52:51 PM
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Benoit Tastet. Structure des noyaux de gallium, de germanium et d'arsenic riches en neutrons autour de N=50 et Développement d'une source d'ionisation laser à ALTO. Physique Nucléaire Théorique [nucl-th]. Université Paris Sud - Paris XI, 2011. Français. ⟨tel-00621073⟩

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