Collective correlations and excitation mechanism of nuclei near the drip-line : developments of cHFB linear response theory

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1.Quantitative aspects of the dineutron correlations in the medium mass near-drip-line O,Ca and Ni isotopes have been clarified by means of the coordinate space HFB theory. Two neutrons with spin singlet configuration are strongly correlated in the short distance region of 2-3fm, where the relative probability of the pair amounts up to 30-50%. The dineutron correlation is most enhanced in the external neutron skin region far outside the nuclear surface by 2-3fm. The correlation is found to exist also in the nuclear interior and in stable nuclei, indicating a generality of this correlation in nuclei.2.Microscopic structure of the dineutron correlation is investigated from the viewpoint of the configuration mixing and the Hartree-Fock single-particle orbits. It is clarified that the orbitals with high angular momenta and high quasiparticle energies contribute to formation of the correlation.3.The dineutron correlation in uniform nuclear matter in the superconducting phase has been investigated. It has been shown that the dineutron correlation is most significant at low densities with 1/5 to 1/100 of normal density. It is also shown that the dineutron correlation is quite general, being independent of the use of the zero or finite range forces.4.The dineutron character of the soft dipole excitation has been investigated in detail by means of the cHFB linear response theory (the continuum QRPA theory) in order to clarify the dominant particle-particle component : Analyzing the single-particle orbits contributing the soft dipole excitation, large contribution of high angular momentum orbittals is found, indicating that the di-neutron correlation plays a central role for this mode.5.We have completed a formulation of the continuum QRPA theory that incorporates the velocity dependent part of the Skyrme interaction for spin independent excitation modes.