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Two new mechanisms active in rotating nuclei located in the vicinity of neutron drip line have been discovered. Strong Coriolis interaction acting on high- j orbitals transforms particle-unbound (resonance) nucleonic configurations into particle-bound ones with increasing angular momentum. The point of the transition manifests the birth of particle-bound rotational bands. Alternative possibility of the transition from particle-bound to resonance rotational band (the death of particle-bound rotational bands) with increasing spin also exists but it is less frequent in the calculations. The birth of particle-bound rotational bands provides a mechanism for the extension of nuclear landscape to neutron numbers which are larger than those of the neutron drip line in non-rotating nuclei. [ABSTRACT FROM AUTHOR]

The formation of intruder states in the low-lying states of 12Be = &agr; + &agr; + 4N is studied by applying the generalized two-center cluster model, which can optimize the excess neutrons' orbits depending on the &agr;-&agr; distance. The correlation energy for the intruder states is analyzed from the viewpoint of two different pictures based on the cluster structure: the covalent picture around two a clusters and the binary He-cluster picture. In the covalent picture, the binding energy of (&pgr;-3/2)2(σ+1/2)2, corresponding to ν(0p)4(Is0d)2 in a naive shell model, gains largely owing to the spin-triplet pairing of the 0d-wave neutrons, which is induced by the two-body spin-orbit interaction. The spin-triplet pairing gives rise to the reduction of the kinetic energy and the increase of the attractive spin-orbit interaction for the excess neutrons. As a result of these correlation energies, the v(0p)4(I0d)2 configuration becomes dominant in the ground state. In the binary cluster picture, the correlation energy is investigated from the coupled channels among &agr; + 8He, 6He + 6He, and 5He + 7He. The coupling to 5He + 7He, which is neglected in usual binary-cluster models, plays an important role for a large reduction of kinetic energy and the formation of a pair of the low-lying 0+ states with a close energy spacing recently observed in experiment. The rotational bands are also discussed from the viewpoint of these two cluster pictures. [ABSTRACT FROM AUTHOR]

We have studied three-α states around 40Ca based on a microscopic α-cluster model.Quite recently experimental evidence for such states has been obtained. This study was performed by introducing a Monte Carlo technique for the description of the THSR (Tohsaki Horiuchi Schuck Röpke) wave function, which is called the "virtual THSR" wave function. The three α cluster state around 40Ca has an energy below the Coulomb barrier top energy with a spatial extension comparable to the second 0+ state of 12C. There is possibility that such gas-like structure of α clusters is stabilized with geometric shape when valence neutrons are added. We also discussed the appearance of geometric α cluster configurations, especially for the linear chain configurations of three α clusters, in neutron-rich C isotopes. [ABSTRACT FROM AUTHOR]

We study the di-neutron correlations in the super neutron-rich nucleus 7H with the AMD triple-S (AMD superposition of selected snapshots). 7H is the most neutron-rich nucleus in the neutron ratio to the proton (N/Z = 6). And the strong di-neutron correlations are expected due to the weak binding properties. In this paper, the mixing of di-neutron cluster components is estimated by calculating the squared overlap with the di-neutron condensate type wave function. The calculated results show significant mixing of di-neutron (t + 2n + 2n) components (70 ~ 80%). [ABSTRACT FROM AUTHOR]

The structure of low-lying states of the carbon isotopes is investigated using the improved version of the Antisymmetrized Molecular Dynamics (AMD) Multi-Slater Determinant model. The theoretical method is found to be very useful to study ground-state properties of various nuclei covering light unstable nuclei. The calculations succeed to reproduce reasonably well many experimental data for the carbon isotopes12C-22C such as binding energies, the energies of the 2+1 states in the even-even isotopes, radii and electromagnetic transition strengths. We investigate the structure change with the increasing neutron number and observe the existence of various exotic phenomena, like the development of a neutron skin and large deformations which appear in unstable nuclei. Our calculations clearly support the existence of theN= 8 andN= 16 neutron magic numbers. The role of the spin-orbit interaction in the description of the studied isotopes and in the development of cluster structures is discussed. A special approach, important for weakly bound systems, is adopted for15C. It enables us to better describe the tail of the wave function. [ABSTRACT FROM AUTHOR]

The properties of nuclei with extreme neutron–to–proton ratios, far from those naturally occurring on Earth, are key to understand nuclear forces and how nucleons hold together to form nuclei. 7H, with six neutrons and a single proton, is the nuclear system with the most unbalanced neutron–to–proton ratio known so far. However, its sheer existence and properties are still a challenge for experimental efforts and theoretical models. Here we report experimental evidences on the formation of 7H as a resonance, detected with independent observables, and the first measurement of the structure of its ground state. The resonance is found at ∼0.7 MeV above the 3H+4n mass, with a narrow width of ∼0.2 MeV and a 1 / 2 + spin and parity. These data are consistent with a 7H as a 3H core surrounded by an extended four-neutron halo, with a unique four-neutron decay and a relatively long half-life thanks to neutron pairing; a prime example of new phenomena occurring in what would be the most pure-neutron nuclear matter we can access in the laboratory. [ABSTRACT FROM AUTHOR]