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The generalized two-center cluster model, which can handle various single particle configurations in general two center systems, is applied to the light neutron-rich system, Be = α+α+4 N. We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. We show that the excess neutrons form various chemical-bonding-like configurations around two α cores in the unbound region above the α decay threshold. The possibility of the α cluster formation in the heavier neutron-excess system, Ne, is also discussed. [ABSTRACT FROM AUTHOR]

The generalized two-center cluster model (GTCM), which can handle various single particle configurations in general two center systems, is applied to the light neutron-rich system, Be = α + α +4 N. We discuss the change of the neutrons' configuration around two α as a variation of an excitation energy. The covalent, ionic and atomic configurations coexists with the degenerate feature above the α + He particle-decay threshold. We find the strong enhancement in the monopole excitation from the ground state to the excited states. The GTCM calculation is also applied to even Be isotopes, and the systematics on the structural changes from bound region to continuum is discussed. [ABSTRACT FROM AUTHOR]

The generalized two-center cluster model (GTCM), which can treat covalent and atomic configurations in general two-center systems, is applied to the light neutron-excess system 12Be = α + α + 4N. The changes of the orbits of the neutrons are analyzed by calculating adiabatic energy surfaces with a variation of the a-a distance. The smooth transition from covalent molecular orbits to atomic He-dimer states is realized in the adiabatic energy surfaces. According to this smooth transition, the adiabatic states are divided into two regions, the internal covalent region and the external He-dimer region, by introducing boundaries of the change in structure. The intrinsic structure of the excited energy levels is investigated. We found that, in an unbound region, the He dimers appear as the molecular resonances of α + 8Heg.s., 6Heg.s. + 6Heg.s., and 5Heg.s. + 7Heg.s. An exotic superdeformation, which has a hybrid configuration of both the covalent and He-dimer structures, is also realized in the same energy region. These unbound states can be classified into internal and external states, and the excitation degrees of freedom are assigned for the individual states. The level scheme of these unbound states reveals a strong degenerate feature with a considerable mixture of the différent configurations. From the result of the level scheme, the "loose clusters" are introduced to characterize the unbound states in the neutron-excess system 12Be. [ABSTRACT FROM AUTHOR]

The monopole excitations (0g.s.+ → 0ex+) of light neutron-excess systems 12Be = α + α + 4N are investigated by the generalized two-center cluster model. We analyze the mechanism of an enhancement of the monopole strength in connection to structures of adiabatic energy surfaces as a function of an a-a distance. The crossing of two adiabatic energy surfaces, which have different intrinsic configurations, increases the monopole strength. Furthermore, we find that the monopole strength is strongly enhanced by a smooth connection in the adiabatic energy surface from the ground 0+ state to the excited 0+ state. A comparison of the calculated strength with the respective single particle limit is also discussed. [ABSTRACT FROM AUTHOR]

The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two center systems, is applied to the light neutron-rich system, 12Be= α+α+4N. We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. We show that the covalent, ionic and atomic configurations appear in the unbound region above the α+8Heg.s. particle-decay threshold, and they coexist within a quite small energy interval. [ABSTRACT FROM AUTHOR]

The condensed states of α-clusters or di-neutrons are studied by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Röpke) wave function. The condensed state of five alpha particles is shown to be stable around the threshold energy even after taking into account the coupling effect between normal cluster states with 16O+α configurations. Next, the mixing of di-neutron components in 8He is studied. The ground state of 8He corresponds to the sub-closed-shell configuration of the spin-orbit favored orbits (p3/2) for the neutrons, and the shell-model-like configuration is considered to be dominant. However, 8He is a drip-line nucleus with a two-neutron separation energy of 2.1 MeV, and the di-neutron configuration, which is a characteristic feature of the weakly bound systems, mixes in the ground state. Finally, characteristic mechanism for the binding of clusters in neutron-rich nuclei (s2 bond) is discussed. [ABSTRACT FROM AUTHOR]