79 research outputs found
Anomalous Properties of Quadrupole Collective States in Te and beyond
The ground and low-lying states of neutron-rich exotic Te and Sn isotopes are
studied in terms of the nuclear shell model by the same Hamiltonian used for
the spherical-deformed shape phase transition of Ba isotopes, without any
adjustment. An anomalously small value is obtained for
in Te, consistently with a recent experiment. The levels of Te
up to yrast are shown to be in agreement with observed ones. It is
pointed out that Te can be an exceptionally suitable case for studying
mixed-symmetry 1, 2 and 3 states, and predictions are made for
energies, M1 and E2 properties. Systematic trends of structure of heavier and
more exotic Sn and Te isotopes beyond Te are studied by Monte Carlo
Shell Model, presenting an unusual and very slow evolution of
collectivity/deformation.Comment: 8 pages, 7 figures, accepted for publication in Phys. Rev.
Onset of intruder ground state in exotic Na isotopes and evolution of the N=20 shell gap
The onset of intruder ground states in Na isotopes is investigated by
comparing experimental data and shell-model calculations. This onset is one of
the consequences of the disappearance of the N=20 magic structure, and the Na
isotopes are shown to play a special role in clarifying the change of this
magic structure. Both the electromagnetic moments and the energy levels clearly
indicate an onset of ground state intruder configurations at neutron number
N=19 already, which arises only with a narrow N=20 shell gap in Na isotopes
resulting from the spin-isospin dependence of the nucleon-nucleon interaction
(as compared to a wider gap in stable nuclei like 40Ca). It is shown why the
previous report based on the mass led to a wrong conclusion.Comment: 9 pages, 6 figures, to be published in Phys. Rev.
Pairing Along the Line
Pairing energies for the addition of two neutrons on even-even nuclei with are studied. The dependence is attributed to the number and type of
orbitals that are occupied in the valence shell-model space. Properties in the
region from depend on the location of the orbital.Comment: 3 pages and 2 figure
Novel features of nuclear forces and shell evolution in exotic nuclei
Novel simple properties of the monopole component of the effective
nucleon-nucleon interaction are presented, leading to the so-called
monopole-based universal interaction. Shell structures are shown to change as
functions of and consistently with experiments. Some key cases of this
shell evolution are discussed, clarifying the effects of central and tensor
forces. The validity of the present tensor force is examined in terms of the
low-momentum interaction V and the Q formalism.Comment: 4 pages, 4 figure
Novel Extrapolation Method in the Monte Carlo Shell Model
We propose an extrapolation method utilizing energy variance in the Monte
Carlo shell model in order to estimate the energy eigenvalue and observables
accurately. We derive a formula for the energy variance with deformed Slater
determinants, which enables us to calculate the energy variance efficiently.
The feasibility of the method is demonstrated for the full -shell
calculation of Ni, and the applicability of the method to a system
beyond current limit of exact diagonalization is shown for the
+-shell calculation of Ge.Comment: 4 pages, 4figure
Nuclear Shell Model by the Quantum Monte Carlo Diagonalization Method
The feasibility of shell-model calculations is radically extended by the
Quantum Monte Carlo Diagonalization method with various essential improvements.
The major improvements are made in the sampling for the generation of
shell-model basis vectors, and in the restoration of symmetries such as angular
momentum and isospin. Consequently the level structure of low-lying states can
be studied with realistic interactions. After testing this method on Mg,
we present first results for energy levels and properties of Ge,
indicating its large and -soft deformation.Comment: 12 pages, RevTex, 2 figures, to be published in Physical Review
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