200 research outputs found
Multipole strength function of deformed superfluid nuclei made easy
We present an efficient method for calculating strength functions using the
finite amplitude method (FAM) for deformed superfluid heavy nuclei within the
framework of the nuclear density functional theory. We demonstrate that FAM
reproduces strength functions obtained with the fully self-consistent
quasi-particle random-phase approximation (QRPA) at a fraction of computational
cost. As a demonstration, we compute the isoscalar and isovector monopole
strength for strongly deformed configurations in Pu by considering huge
quasi-particle QRPA spaces. Our approach to FAM, based on Broyden's iterative
procedure, opens the possibility for large-scale calculations of strength
distributions in well-bound and weakly bound nuclei across the nuclear
landscape.Comment: 5 pages, 3 figure
Mirror and triplet displacement energies within nuclear DFT : Numerical stability
Isospin-symmetry-violating class II and III contact terms are introduced into the Skyrme energy density functional to account for charge dependence of the strong nuclear interaction. The two new coupling constants are adjusted to available experimental data on triplet and mirror displacement energies, respectively. We present preliminary results of the fit, focusing on its numerical stability with respect to the basis size.Peer reviewe
Nuclear charge-exchange excitations in localized covariant density functional theory
The recent progress in the studies of nuclear charge-exchange excitations
with localized covariant density functional theory is briefly presented, by
taking the fine structure of spin-dipole excitations in 16O as an example. It
is shown that the constraints introduced by the Fock terms of the relativistic
Hartree-Fock scheme into the particle-hole residual interactions are
straightforward and robust.Comment: 4 pages, 1 figure, Proceedings of INPC2013, Florence, Italy, 2-7 June
201
Self-consistent calculation of nuclear photoabsorption cross section: Finite amplitude method with Skyrme functionals in the three-dimensional real space
The finite amplitude method (FAM), which we have recently proposed (T.
Nakatsukasa, T. Inakura, and K. Yabana, Phys. Rev. C 76, 024318 (2007)),
simplifies significantly the fully self-consistent RPA calculation. Employing
the FAM, we are conducting systematic, fully self-consistent response
calculations for a wide mass region. This paper is intended to present a
computational scheme to be used in the systematic investigation and to show the
performance of the FAM for a realistic Skyrme energy functional. We implemented
the method in the mixed representation in which the forward and backward RPA
amplitudes are represented by indices of single-particle orbitals for occupied
states and the spatial grid points for unoccupied states. We solve the linear
response equation for a given frequency. The equation is a linear algebraic
problem with a sparse non-hermitian matrix, which is solved with an iterative
method. We show results of the dipole response for selected spherical and
deformed nuclei. The peak energies of the giant dipole resonance agree well
with measurements for heavy nuclei, while they are systematically
underestimated for light nuclei. We also discuss the width of the giant dipole
resonance in the fully self-consistent RPA calculation.Comment: 11 pages, 10 figure
Isospin-symmetry breaking in masses of N similar or equal to Z nuclei
Effects of the isospin-symmetry breaking (ISB) beyond mean-field Coulomb terms are systematically studied in nuclear masses near the N = Z line. The Coulomb exchange contributions are calculated exactly. We use extended Skyrme energy density functionals (EDFs) with proton-neutron-mixed densities, to which we add new terms breaking the isospin symmetry. Two parameters associated with the new terms are determined by fitting mirror and triplet displacement energies (MDEs and TDEs) of isospin multiplets. The new EDFs reproduce MDEs for the T = 1/2 doublets and T= 1 triplets, and TDEs for the T= 1 triplets. Relative strengths of the obtained isospin-symmetry-breaking terms are not consistent with the differences in the NN scattering lengths, a(nn), a(pp), and a(np). Based on low-energy experimental data, it seems thus impossible to delineate the strong-force ISB effects from beyond-mean-field Coulomb-energy corrections. (C) 2018 The Author(s). Published by Elsevier B.V.Peer reviewe
Microscopic Structure of High-Spin Vibrational Excitations in Superdeformed 190,192,194Hg
Microscopic RPA calculations based on the cranked shell model are performed
to investigate the quadrupole and octupole correlations for excited
superdeformed bands in 190Hg, 192Hg, and 194Hg. The K=2 octupole vibrations are
predicted to be the lowest excitation modes at zero rotational frequency. At
finite frequency, however, the interplay between rotation and vibrations
produces different effects depending on neutron number: The lowest octupole
phonon is rotationally aligned in 190Hg, is crossed by the aligned
two-quasiparticle bands in 192Hg, and retains the K=2 octupole vibrational
character up to the highest frequency in 194Hg. The gamma vibrations are
predicted to be higher in energy and less collective than the octupole
vibrations. From a comparison with the experimental dynamic moments of inertia,
a new interpretation of the observed excited bands invoking the K=2 octupole
vibrations is proposed, which suggests those octupole vibrations may be
prevalent in SD Hg nuclei.Comment: 22 pages, REVTeX, 12 postscript figures are available on reques
Isospin-symmetry breaking in masses of N ≃ Z nuclei
Effects of the isospin-symmetry breaking (ISB) beyond mean-field Coulomb terms are systematically studied in nuclear masses near the N=Z line. The Coulomb exchange contributions are calculated exactly. We use extended Skyrme energy density functionals (EDFs) with proton–neutron-mixed densities, to which we add new terms breaking the isospin symmetry. Two parameters associated with the new terms are determined by fitting mirror and triplet displacement energies (MDEs and TDEs) of isospin multiplets. The new EDFs reproduce MDEs for the T=1/2 doublets and T=1 triplets, and TDEs for the T=1 triplets. Relative strengths of the obtained isospin-symmetry-breaking terms are not consistent with the differences in the NN scattering lengths, a nn, a pp, and a np. Based on low-energy experimental data, it seems thus impossible to delineate the strong-force ISB effects from beyond-mean-field Coulomb-energy corrections
Relative spins and excitation energies of superdeformed bands in 190Hg: Further evidence for octupole vibration
An experiment using the Eurogam Phase II gamma-ray spectrometer confirms the
existence of an excited superdeformed (SD) band in 190Hg and its very unusual
decay into the lowest SD band over 3-4 transitions. The energies and dipole
character of the transitions linking the two SD bands have been firmly
established. Comparisons with RPA calculations indicate that the excited SD
band can be interpreted as an octupole-vibrational structure.Comment: 12 pages, latex, 4 figures available via WWW at
http://www.phy.anl.gov/bgo/bc/hg190_nucl_ex.htm
Tilted Rotation and Wobbling Motion in Nuclei
The self-consistent harmonic oscillator model including the three-dimensional
cranking term is extended to describe collective excitations in the random
phase approximation. It is found that quadrupole collective excitations
associated with wobbling motion in rotating nuclei lead to the appearance of
two- or three-dimensional rotation.Comment: 9 pages, 2 Postscript figures, corrected typo
The nuclear energy density functional formalism
The present document focuses on the theoretical foundations of the nuclear
energy density functional (EDF) method. As such, it does not aim at reviewing
the status of the field, at covering all possible ramifications of the approach
or at presenting recent achievements and applications. The objective is to
provide a modern account of the nuclear EDF formalism that is at variance with
traditional presentations that rely, at one point or another, on a {\it
Hamiltonian-based} picture. The latter is not general enough to encompass what
the nuclear EDF method represents as of today. Specifically, the traditional
Hamiltonian-based picture does not allow one to grasp the difficulties
associated with the fact that currently available parametrizations of the
energy kernel at play in the method do not derive from a genuine
Hamilton operator, would the latter be effective. The method is formulated from
the outset through the most general multi-reference, i.e. beyond mean-field,
implementation such that the single-reference, i.e. "mean-field", derives as a
particular case. As such, a key point of the presentation provided here is to
demonstrate that the multi-reference EDF method can indeed be formulated in a
{\it mathematically} meaningful fashion even if does {\it not} derive
from a genuine Hamilton operator. In particular, the restoration of symmetries
can be entirely formulated without making {\it any} reference to a projected
state, i.e. within a genuine EDF framework. However, and as is illustrated in
the present document, a mathematically meaningful formulation does not
guarantee that the formalism is sound from a {\it physical} standpoint. The
price at which the latter can be enforced as well in the future is eventually
alluded to.Comment: 64 pages, 8 figures, submitted to Euroschool Lecture Notes in Physics
Vol.IV, Christoph Scheidenberger and Marek Pfutzner editor
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