1,279 research outputs found
Charge-exchange dipole excitations in neutron-rich nuclei: , anti-analog pygmy, and anti-analog giant resonances
The occurrence of the low-lying charge-exchange non spin-flip dipole modes
below the giant resonance in neutron-rich nuclei is predicted on the basis of
nuclear density functional theory. The ground and excited states are described
in the framework of the self-consistent Hartree-Fock-Bogoliubov and the
proton-neutron quasiparticle-random-phase approximation employing a Skyrme-type
energy density functional. The model calculations are performed for the
spherical neutron-rich Ca, Ni, and Sn isotopes. It is found that the low-lying
states appear sensitively to the shell structure associated with the excitation below the Gamow-Teller states. Furthermore, the pygmy
resonance emerges below the giant resonance when the neutrons occupy the
low- orbitals analogous to the pygmy resonance seen in
the electric dipole response.Comment: 5 pages, 5 figure
Suddenly shortened half-lives beyond Ni: magic number and high-energy non-unique first-forbidden transitions
-decay rates play a decisive role in understanding the nucleosynthesis
of heavy elements and are governed by microscopic nuclear-structure
information. A sudden shortening of the half-lives of Ni isotopes beyond
was observed at the RIKEN-RIBF. This is considered due to the persistence of
the neutron magic number in the very neutron-rich Ni isotopes. By
systematically studying the -decay rates and strength distributions in
the neutron-rich Ni isotopes around , I try to understand the microscopic
mechanism for the observed sudden shortening of the half-lives. The
-strength distributions in the neutron-rich nuclei are described in the
framework of nuclear density-functional theory. I employ the Skyrme
energy-density functionals (EDF) in the Hartree-Fock-Bogoliubov calculation for
the ground states and in the proton-neutron Quasiparticle Random-Phase
Approximation (pnQRPA) for the transitions. Not only the allowed but the
first-forbidden (FF) transitions are considered. The experimentally observed
sudden shortening of the half-lives beyond is reproduced well by the
calculations employing the Skyrme SkM* and SLy4 functionals. The sudden
shortening of the half-lives is due to the shell gap at and
cooperatively with the high-energy transitions to the low-lying and
states in the daughter nuclei. The onset of FF transitions pointed out around
and 126 is preserved in the lower-mass nuclei around . This study
suggests that needed is a microscopic calculation where the shell structure in
neutron-rich nuclei and its associated effects on the FF transitions are
selfconsistenly taken into account for predicting -decay rates of exotic
nuclei in unknown region.Comment: 8 pages, 7 figures and 1 tabl
Skyrme-QRPA calculations for low-lying excitation modes in deformed neutron-rich nuclei
Low-frequency modes of excitation in deformed neutron-rich nuclei are studied
by means of the quasiparticle random-phase approximation on the
Skyrme-Hartree-Fock-Bogoliubov mean field. We investigate the microscopic
structure of the soft modes systematically in neutron-rich
Magnesium isotopes with and 28 close to the drip line, and it is
found that the strong collectivity in Mg and Mg is acquired due
to the coherent coupling between the vibration and the pairing
vibration of neutrons. Microscopic structure of the modes
changes gradually associated with the location of the Fermi level of neutrons,
and it is found that the proton particle-hole excitation generating the
vibrational mode in Mg continues to play a key role in the
near-drip-line nucleus Mg. The low-frequency octupole excitations are
also investigated and the microscopic mechanism for the enhancement of
transition strengths is discussed.Comment: Accepted for publication in Eur. Phys. J. A, as a contribution to the
ENAM08 conferenc
Dynamic Pairing Effects on Low-Frequency Modes of Excitation in Deformed Mg Isotopes close to the Neutron Drip Line
Low-frequency quadrupole vibrations in deformed Mg are studied
by means of the deformed Quasiparticle-RPA based on the coordinate-space
Hartree-Fock-Bogoliubov formalism. Strongly collective and
excitation modes (carrying 10-20 W.u.) are obtained at about 3 MeV. It
is found that dynamical pairing effects play an essential role in generating
these modes. It implies that the lowest excitation modes are
particularly sensitive indicators of dynamical pairing correlations in deformed
nuclei near the neutron drip line.Comment: Talk given at Int. Conference "Finite Fermionic Systems: Nilsson
Model 50 Years", Lund, Sweden, June 14-18, 200
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