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Transition de forme à haut spin dans le noyau octupolaire de thorium 223 et autres aspects méthodologiques de la spectroscopie gamma moderne

Abstract : The first part focuses on the experimental aspects and allowed us, initially, to introduce the three ? detectors of interest for my thesis. In a second step, rather than detailing traditional data analysis procedures, we have chosen to introduce a new formalism for the calculation of relative intensities in a spectrum. This formalism calls into question the method traditionally used. In order to always save time, and in order to go further in the analysis methods, a collaborative work was put in place to develop the Cubix software. This collaborative work on this software has resulted in an ergonomic version, complete and including new features. One of the perspectives of this work would be to implement the formalism on the intensities in Cubix.The second part focuses on the interpretation of the data obtained from the JUROGAM II and EUROBALL IV experiments. The simultaneous analysis of these two experiments yielded solid and convincing experimental results. The analysis of theHigh spin in the nucleus of 223Th has shown for the first time in the isotopes of Thorium, a sudden increase in its moment of inertia. This phenomenon has been interpreted as the first indications of a quadrupole to octupole-quadrupole (rugby ball-pear), high-spin type change. On the same theme, some perspectives were raised:(I) Collaboration with the IPNL theory group to perform a more accurate interpretation of the observed phenomenon;(Ii) Experimental proposal to determine the onset of octupole deformation in Neutron-poor Thorium isotopes;(Iii) Characterization of the quadrupole band with four quasiparticles aligned in the isotopes of 222,223,224Th. This represents a huge experimental challenge, requiring the use of very high-efficiency detectors.Finally, the last part deals with the results of the AGATA + VAMOS experiment at GANIL. A new level scheme for the exotic nucleus 81Ga has been proposed. The last excitation state observed at 2759 keV (spin I = 13/2 -) was discussed as an indication of a large N = 50 shell closure. Extrapolations concerning the doubly magic character of the 78Ni nucleus can be considered as perspectives of this work
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Guillaume Maquart. Transition de forme à haut spin dans le noyau octupolaire de thorium 223 et autres aspects méthodologiques de la spectroscopie gamma moderne. Physique Nucléaire Expérimentale [nucl-ex]. Université de Lyon, 2017. Français. ⟨NNT : 2017LYSE1135⟩. ⟨tel-01684908⟩

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