2,397 research outputs found
Systematics of 2+ states in semi-magic nuclei
We propose a simple systematics of low lying 2+ energy levels and
electromagnetic transitions in semi-magic isotopic chains Z=28,50,82 and
isotonic chains N=28,50,82,126. To this purpose we use a two-level pairing plus
quadrupole Hamiltonian, within the spherical Quasiparticle Random Phase
Approximation (QRPA). We derive a simple relation connecting the 2+ energy with
the pairing gap and quadrupole-quadupole (QQ) interaction strength. It turns
out that the systematics of energy levels and B(E2) values predicted by this
simple model is fulfilled with a reasonable accuracy by all available
experimental data. Both systematics suggest that not only active nucleons but
also those filling closed shells play an important role
Giant monopole resonance and nuclear compression modulus for 40Ca and 16O
Using a collective potential derived on the basis of the Generator Coordinate
Method with Skyrme interactions we obtain values for the compression modulus of
40Ca which are in good agreement with a recently obtained experimental value.
Calculated values for the compression modulus for 16O are also given. The
procedure involved in the derivation of the collective potential is briefly
reviewed and discussed.Comment: 14 pages, no figures, two tables, REVTE
Canonical-basis solution of the Hartree-Fock-Bogoliubov equation on three-dimensional Cartesian mesh
A method is presented to obtain the canonical-form solutions of the HFB
equation for atomic nuclei with zero-range interactions like the Skyrme force.
It is appropriate to describe pairing correlations in the continuum in
coordinate-space representations. An improved gradient method is used for
faster convergences under constraint of orthogonality between orbitals. To
prevent high-lying orbitals to shrink into a spatial point, a repulsive
momentum dependent force is introduced, which turns out to unveil the nature of
high-lying canonical-basis orbitals. The asymptotic properties at large radius
and the relation with quasiparticle states are discussed for the obtained
canonical basis.Comment: 23 pages including 17 figures, REVTeX4, revised version, scheduled to
appear in Phys. Rev. C, Vol.69, No.
Relativistic Mean Field Approach and the Pseudo-Spin Symmetry
Based on the Relativistic Mean Field (RMF) approach the existence of the
broken pseudo-spin symmetry is investigated. Both spherical RMF and constrained
deformed RMF calculations are carried out employing realistic Lagrangian
parameters for spherical and for deformed sample nuclei. The quasi - degenerate
pseudo-spin doublets are confirmed to exist near the fermi surface for both
spherical and deformed nuclei.Comment: 9 pages RevTex, 4 p.s figures, to appear in Phys. Rev. C as R.
Finite-size effects and collective vibrations in the inner crust of neutron stars
We study the linear response of the inner crust of neutron stars within the
Random Phase Approximation, employing a Skyrme-type interaction as effective
interaction. We adopt the Wigner-Seitz approximation, and consider a single
unit cell of the Coulomb lattice which constitutes the inner crust, with a
nucleus at its center, surrounded by a sea of free neutrons. With the use of an
appropriate operator, it is possible to analyze in detail the properties of the
vibrations of the surface of the nucleus and their interaction with the modes
of the sea of free neutrons, and to investigate the role of shell effects and
of resonant states
Nuclear Pairing: Surface or Bulk ?
We analyse how the spatial localisation properties of pairing correlations
are changing in a major neutron shell of heavy nuclei. It is shown that the
radial distribution of the pairing density depends strongly on whether the
chemical potential is close to a low or a high angular momentum level and has
very little sensitivity to whether the pairing force acts in the surface or in
the bulk. The averaged pairing density over one major shell is however rather
flat, practically independent of the pairing force. Hartree-Fock-Bogoliubov
calculations for the isotopic chain Sn are presented for
demonstration purposes.Comment: 12 pages, 5 figure
Equivalence of particle-particle random phase approximation correlation energy and ladder-coupled-cluster doubles
We present an analytical proof and numerical demonstrations of the
equivalence of the correlation energy from particle-particle random phase
approximation (pp-RPA) and ladder-couple-cluster-doubles (ladder-CCD). These
two theories reduce to the identical algebraic matrix equation and correlation
energy expressions, under the assumption that the pp-RPA equation is stable.
The numerical examples illustrate that the correlation energy missed by pp-RPA
in comparison with couple-cluster single and double is largely canceled out
when considering reaction energies. This theoretical connection will be
beneficial to future pp-RPA studies based on the well established couple
cluster theory
Two-neutron transfer in nuclei close to the dripline
We investigate the two-neutron transfer modes induced by (t,p) reactions in
neutron-rich oxygen isotopes. The nuclear response to the pair transfer is
calculated in the framework of continuum-Quasiparticle Random Phase
Approximation (cQRPA). The cQRPA allows a consistent determination of the
residual interaction and an exact treatment of the continuum coupling. The
(t,p) cross sections are calculated within the DWBA approach and the form
factors are evaluated by different methods : macroscopically, following the
Bayman and Kallio method, and fully microscopically. The largest cross section
corresponds to a high-lying collective mode built entirely upon continuum
quasiparticle states.Comment: 12 pages, 7 figure
Semi-microscopic description of the backbending phenomena in some deformed even-even nuclei
The mechanism of backbending is semi-phenomenologically investigated based on
the hybridization of two rotational bands. These bands are defined by treating
a model Hamiltonian describing two interacting subsystems: a set of particles
moving in a deformed mean field and interacting among themselves through an
effective pairing force and a phenomenological deformed core whose intrinsic
ground state is an axially symmetric coherent boson state. The two components
interact with each other by a quadrupole-quadrupole and a spin-spin
interaction. The total Hamiltonian is considered in the space of states with
good angular momentum, projected from a quadrupole deformed product function.
The single-particle factor function defines the nature of the rotational bands,
one corresponding to the ground band in which all particles are paired and
another one built upon a neutron broken pair. The formalism is
applied to six deformed even-even nuclei, known as being good backbenders.
Agreement between theory and experiment is fairly good.Comment: 37 pages, 9 figure
Hartree-Fock and Many-Body Perturbation Theory with Correlated Realistic NN-Interactions
We employ correlated realistic nucleon-nucleon interactions for the
description of nuclear ground states throughout the nuclear chart within the
Hartree-Fock approximation. The crucial short-range central and tensor
correlations, which are induced by the realistic interaction and cannot be
described by the Hartree-Fock many-body state itself, are included explicitly
by a state-independent unitary transformation in the framework of the unitary
correlation operator method (UCOM). Using the correlated realistic interaction
V_UCOM resulting from the Argonne V18 potential, bound nuclei are obtained
already on the Hartree-Fock level. However, the binding energies are smaller
than the experimental values because long-range correlations have not been
accounted for. Their inclusion by means of many-body perturbation theory leads
to a remarkable agreement with experimental binding energies over the whole
mass range from He-4 to Pb-208, even far off the valley of stability. The
observed perturbative character of the residual long-range correlations and the
apparently small net effect of three-body forces provides promising
perspectives for a unified nuclear structure description.Comment: 14 pages, 8 figures, 3 tables, using REVTEX
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