Mémoires de Fin d’Etudes
Etablissement
Université de Sétif 1 - Ferhat Abbas
Affiliation
Département de Physique
Auteur
ABDERRAHMANE, Yakhelef
Directeur de thèse
A. Boucenna (Professeur)
Co-directeur
A. Bouldjedri (Professeur)
Filière
Physique
Diplôme
Doctorat
Titre
Study of nuclei far from stability in the vicinity of 100Sn and light nuclei using microscopic models Viva
Mots clés
The three-body calculations suggest that a 2+ state-the abundances of actinides
Résumé
We have studied the 18C spectrum within a three-body deformed 16C+n+n model with 2+ excitation of the 16C core. This study reveals that the bound state energy of 18C is compatible with the three-body structure of this nucleus. Our model gives the energy of the first excited 2+ state within 0.4 MeV of the experimentally observed one and suggest that there should exist another 2+ state around 4 MeV, which is compatible with recent experimental studies. However, our model gives low positions of the first 4+ and 1+ levels, which could be a drawback of the 17C+n interaction used. Although this interaction reproduces exactly the observed spectrum of 17C, its composition in terms of probabilities of the core states is not reproduced. Including more excitation, for example, by adding the 16C(4+) into the coupled channel problem, could improve this situation, however it would increase the number of channels in the three-body problem to such extent that it would make such calculations impossible. Our calculations suggest that there may be resonances in the region between the 17C+n and 16C+2n thresholds, the most important of which is 1−. Interestingly, the recent analysis of the two-neutron knockout from 19C [22] suggests that the important part of the removal cross section comes from population of the intermediate 1− state in 18C. If this resonance has a threebody structure and a large E1 strength associated with it, then it will give a large contribution to the 17C(n,γ)18C capture rate. The increased reaction rate may significantly influence the abundances of actinides synthesized in the r-process and, therefore, a search for this resonance is an important and timely task. The three-body calculations suggest that a 2+ state may be present in the astrophysical relevant region between the 16C+2n and 17C+n. This state should have a significant s-wave component in which the valence neutron does not see any centrifugal barrier. Such a state may manifest itself as a virtual state in the 17C+n continuum. To calculate the contribution from this state correctly, a scattering three-body problem includes a binary channel 5.3 Summary and Conclusions 69 should be solved. This problem should also include core excitations and Pauli projection of forbidden states, which is too complicated at the moment. However, it is very important to perform such calculations properly because the presence of a virtual s-wave states could lead to an enhanced neutron M1 capture rate. Predictions for strong M1 enhancement have been recently made for a similar reaction, 17F(p,γ)18Ne, in the Gamow shell model [23].
Date de soutenance
2011
Cote
TH789
Pagination
144
Illusatration
ill
Format
C.D
Statut
Soutenue