Giacomo de Angelis, INFN Legnaro
Vendredi 16 mars 2007 à 10h30 - Salle des Séminaires
Magic numbers are a key feature in finite Fermion systems since they are strongly related to the underlying mean field. The study of the evolution of the shells far from stability is therefore of high interest since such information can be linked to the shape and symmetry of the nuclear mean field. The study of nuclei with large neutron/proton ratio allow to probe the density dependence of the effective interaction. Changes of the nuclear density and size in nuclei with increasing N/Z ratios are expected to lead to different nuclear symmetries and excitations. On the proton rich side mirror nuclei provide a privileged viewpoint to test our understanding of isospin symmetry. In particular, if isospin symmetry holds and in the long wavelength limit, E1 transitions are purely isovector in nature and should thus exhibit equal reduced strengths. Breaking of the symmetry translates into the presence of an induced isoscalar component. Differences in the mirror B(E1) strengths are due to the interference between the isovector term and the induced isoscalar term and can be used to determine the amount of isospin mixing. The study of nuclear structure far from stability, which mainly rely on the availability of radioactive nuclear beams, can complementary be addressed by means of high intensity beams of stable ions. Deep-inelastic and multi-nucleon transfer reactions are a powerful tool to populate yrast and non yrast states in neutron-rich nuclei. Particularly successful is here the combination of large acceptance spectrometers with highly segmented g-detector arrays. Such devices, eventually complemented by large coverage particle detectors, can provide the necessary channel selectivity to identify very rare signals.
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