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Application du modèle en couches à l'étude des états intrus de parité négative des noyaux sd moyennant la nouvelle interaction PSDPF

Abstract : The nuclear structure of the sd shell nuclei has been well studied experimentally near the stability line and more recently the interest has been focused on the neutron rich nuclei. The normal positive parity states are well described using the USD interaction in the 0ħω sd shell space (0ħω space) with an 16O core. This interaction has recently been updated and the obtained new Hamiltonians are called USDA and USDB. The experimental spectra show the existence, in addition of the normal states, of a set of negative parity states named "intruder states", resulting from the excitation of one nucleon from the p to the sd shell for nuclei near 16O or from the sd to the fp shell for nuclei close to 40Ca. In the middle of the sd shell there is a competition between the two types of excitations for the intruders. Before our work, no unified description of the negative parity states throughout the complete sd shell existed. To study the intruder states we must enlarge the model space from the sd space (16O core) to the full p-sd-pf space (4He core) which is named 1ħω space. This requires the construction of a new interaction compatible with this extended shell model space. Such a procedure is now possible due to the today increased computational power. We have thus developed for the first time a 1ħω interaction called PSDPF, which has five distinctive parts: p, sd and pf shells and cross p-sd and sd-pf shells. The fixed three interactions for the p, sd and pf shells are respectively: CK, USDB and SDPF-NR, the latter one contains also the sd-pf two body matrix elements, the p-sd interaction is taken to be the PSDT interaction. We have modified the cross p-sd and sd-pf shells contributions to reproduce the energy evolution of the intruder states of different spins throughout the complete sd shell. This new interaction was used to calculate intruder states in the sd nuclei with N = Z and Z + 1. The energy spectra of + and - states in all sd nuclei were also calculated. The comparison experience-theory shows a very good agreement and gives thus credit to our new proposed interaction to describe the intruder states of the sd shell. States of parity - were attributed to some unknown Jπ levels. The reduced electromagnetic transitions probabilities E2 and E3 of the first states of parity + and -, with Jπ = 2+ and 3- in even-even nuclei, were also calculated and the effective charges for the E3 transitions were studied for the first time.
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Submitted on : Monday, December 12, 2011 - 8:24:15 PM
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  • HAL Id : tel-00651110, version 1

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Mouna Bouhelal. Application du modèle en couches à l'étude des états intrus de parité négative des noyaux sd moyennant la nouvelle interaction PSDPF. Physique Nucléaire Théorique [nucl-th]. Université de Strasbourg; Université de Batna, 2010. Français. ⟨tel-00651110⟩

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