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Etude de la structure du $^{44}$S par sa décroissance isomérique

Abstract : The study of atomic nucleus aims at improving our knowledge about the nuclear interaction that is responsible for the cohesion in the nucleus. At first, stable nuclei (Z≈N) were studied and an expression of the nuclear interaction was derived. At this era, one of the goals was to reproduce unusual properties of the ”magic”nuclei. With the development of accelerators, neutrons rich or deficient nuclei were produced giving the opportunity to study the evolution of nuclearinteraction as a function of isospin value. Since the nineties, studies about exotic nuclei with N=28 neutrons have shown that the ”magic” behavior of N=28 vanish far from stability. In particular, $^{44}$S (Z=16, N=28) is found to be deformed in its ground state. Theoretically, shell model calculations predict a spherical-deformed shape coexistence whereas a deformed-deformed shape coexistence is predicted from mean field theories. In 2005, a second $0^+$ state was discovered at low excitation energy confirming the shape coexistence without giving answers about the type of deformations. The goal of the experiment presented here was to characterize this shape coexistence by measuring the reduced transition probability B(E2 ; $0^+_2$ → $2^+_1$ ) and the monopolar transiton strength $ρ^2$(E0; $0^+_2$ → $0^+_1$). An interpretation about $0^+$ states mixing is suggested from the measured low B(E2 ; $0^+_2$ → $2^+_1$ ) value as well as a comparison with shell model calculations. A low $ρ^2$ value was also measured and compared to systematics. Interpretations in both shell model and geometrical collective model are suggested.
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Submitted on : Thursday, November 5, 2009 - 5:10:06 PM
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Carole Force. Etude de la structure du $^{44}$S par sa décroissance isomérique. Physique Nucléaire Expérimentale [nucl-ex]. Université de Caen, 2009. Français. ⟨tel-00430125⟩

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