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HK: Hadronen und Kerne
HK 6: Spectroscopy, Light Nuclei
HK 6.6: Group Report
Monday, March 16, 1998, 16:00–16:30, D
Structure and Reactions of Halo–Nuclei — •H. Lenske1, T. Baumann2, H. Geissel2, and G. Schrieder3 — 1Institut für Theoretische Physik, Universität Giessen — 2GSI Darmstadt, 19C Collaboration — 3TU Darmstadt
In recent experiments new regions of light dripline nuclei have been explored allowing to study the dynamics of halo systems systematically. Of particular interest for nuclear structure are the neutron–rich carbon isotopes 17,19C for which breakup momentum distributions have been measured recently at GSI. In these nuclides the last neutron is coupled to a core which by itself is located far off stability. Theoretically, the coupling is described in a microscopic core polarization approach. Because the core nuclei are easily excited the motion of the valence neutron is strongly affected by dynamical polarization self–energies. The self–energies are obtained by coupling the outer neutron to RPA excitations of the core including core states up to the giant resonance region. Also, the polarizability of the core nuclei is obtained from the RPA calculations. With core polarization the valence level structure is changed resulting in a redistribution of single particle strength in the 2s and 1d valence shells. Core polarization is found to contribute strongly both in 17C to 19C. Static mean–field dynamics are being replaced increasingly by non-static interactions. Shell structures are dissolved as seen by the near degeneracy of 1/2+ and 5/2+ configurations. In both nuclei, core excited components account for more than 50% of the g.s. wave functions. The width of momentum distributions from high energetic breakup reactions is a sensitive indicator of core polarization effects. However, contributions from reaction dynamics have the tendency to reduce the width. Low energy transfer reactions in inverse kinematics are discussed as an alternative approach to the spectroscopy of nuclei far off stability. Exploratory calculations for one– and two–nucleon transfer reactions on light and heavy neutron–rich nuclei show that the special features of weakly bound systems lead to a particular sensitivity of transfer reactions on the tails of wave functions. Different from the experience with stable projectiles, the cross section reach a maximum at low inicdent energies, typically around Elab≃2⋯3 MeV/u.
Supported by DFG and GSI