1,278 research outputs found
Systematics of quadrupolar correlation energies
We calculate correlation energies associated with the quadrupolar shape
degrees of freedom with a view to improving the self-consistent mean-field
theory of nuclear binding energies. The Generator Coordinate Method is employed
using mean-field wave functions and the Skyrme SLy4 interaction. Systematic
results are presented for 605 even-even nuclei of known binding energies, going
from mass A=16 up to the heaviest known. The correlation energies range from
0.5 to 6.0 MeV in magnitude and are rather smooth except for large variations
at magic numbers and in light nuclei. Inclusion of these correlation energies
in the calculated binding energy is found to improve two deficiencies of the
Skyrme mean field theory. The pure mean field theory has an exaggerated shell
effect at neutron magic numbers and addition of the correlation energies reduce
it. The correlations also explain the phenomenon of mutually enhanced magicity,
an interaction between neutron and proton shell effects that is not explicable
in mean field theory.Comment: 4 pages with 3 embedded figure
The Spectral Line Shape of Exotic Nuclei
The quadrupole strength function of is calculated making use of the
SIII interaction, within the framework of continuum-RPA and taking into account
collisions among the nucleons (doorway coupling). The centroid of the giant
resonance is predicted at MeV, that is much below the energy
expected for both isoscalar and isovector quadrupole resonances in nuclei along
the stability valley. About half of this width arises from the coupling of the
resonance to the continuum and about half is due to doorway coupling. This
result is similar to that obtained in the study of giant resonances in light,
-stable nuclei, and shows the lack of basis for the expectation,
entertained until now in the literature, that continuum decay was the main
damping mechanism of giant resonances in halo nuclei.Comment: LaTeX file, 7 pages, figures not included but available if requested
at [email protected], accepted for publication in Phys. Rev.
Global study of quadrupole correlation effects
We discuss the systematics of ground-state quadrupole correlations of binding
energies and mean-square charge radii for all even-even nuclei, from O16 up to
the superheavies, for which data are available. To that aim we calculate their
correlated J=0 ground state by means of the angular-momentum and
particle-number projected generator coordinate method, using the axial mass
quadrupole moment as the generator coordinate and self-consistent mean-field
states only restricted by axial, parity, and time-reversal symmetries. The
calculation is performed within the framework of a non-relativistic
self-consistent mean-field model using the same non-relativistic Skyrme
interaction SLy4 and a density-dependent pairing force to generate the
mean-field configurations and mix them. (See the paper for the rest of the
abstract).Comment: 28 pages revtex, 29 eps figures (2 of which in color), 10 tables.
submitted to Phys. Rev.
Mean field and pairing properties in the crust of neutron stars
Properties of the matter in the inner crust of a neutron star are
investigated in a Hartree-Fock plus BCS approximation employing schematic
effective forces of the type of the Skyrme forces. Special attention is paid to
differences between a homogenous and inhomogeneous description of the matter
distribution. For that purpose self-consistent Hartree Fock calculations are
performed in a spherical Wigner-Seitz cell. The results are compared to
predictions of corresponding Thomas Fermi calculations. The influence of the
shell structure on the formation of pairing correlations in inhomogeneous
matter are discussed.Comment: 11 pages, 9 figure
Extracting particle freeze-out phase-space densities and entropies from sources imaged in heavy-ion reactions
The space-averaged phase-space density and entropy per particle are both
fundamental observables which can be extracted from the two-particle
correlation functions measured in heavy-ion collisions. Two techniques have
been proposed to extract the densities from correlation data: either by using
the radius parameters from Gaussian fits to meson correlations or by using
source imaging, which may be applied to any like pair correlation. We show that
the imaging and Gaussian fits give the same result in the case of meson
interferometry. We discuss the concept of an equivalent instantaneous source on
which both techniques rely. We also discuss the phase-space occupancy and
entropy per particle. Finally, we propose an improved formula for the
phase-space occupancy that has a more controlled dependence on the uncertainty
of the experimentally measured source functions.Comment: 14 pages, final version, to appear PRC. Fixed typos, added refs. for
last section, added discussions of imaging and d/p ratio
Correlation energies by the generator coordinate method: computational aspects for quadrupolar deformations
We investigate truncation schemes to reduce the computational cost of
calculating correlations by the generator coordinate method based on mean-field
wave functions. As our test nuclei, we take examples for which accurate
calculations are available. These include a strongly deformed nucleus, 156Sm, a
nucleus with strong pairing, 120Sn, the krypton isotope chain which contains
examples of soft deformations, and the lead isotope chain which includes the
doubly magic 208Pb. We find that the Gaussian overlap approximation for angular
momentum projection is effective and reduces the computational cost by an order
of magnitude. Cost savings in the deformation degrees of freedom are harder to
realize. A straightforward Gaussian overlap approximation can be applied rather
reliably to angular-momentum projected states based on configuration sets
having the same sign deformation (prolate or oblate), but matrix elements
between prolate and oblate deformations must be treated with more care. We
propose a two-dimensional GOA using a triangulation procedure to treat the
general case with both kinds of deformation. With the computational gains from
these approximations, it should be feasible to carry out a systematic
calculation of correlation energies for the nuclear mass table.Comment: 11 pages revtex, 9 eps figure
Structure of even-even nuclei using a mapped collective Hamiltonian and the D1S Gogny interaction
A systematic study of low energy nuclear structure at normal deformation is
carried out using the Hartree-Fock-Bogoliubov theory extended by the Generator
Coordinate Method and mapped onto a 5-dimensional collective quadrupole
Hamiltonian. Results obtained with the Gogny D1S interaction are presented from
dripline to dripline for even-even nuclei with proton numbers Z=10 to Z=110 and
neutron numbers N less than 200. The properties calculated for the ground
states are their charge radii, 2-particle separation energies, correlation
energies, and the intrinsic quadrupole shape parameters. For the excited
spectroscopy, the observables calculated are the excitation energies and
quadrupole as well as monopole transition matrix elements. We examine in this
work the yrast levels up to J=6, the lowest excited 0^+ states, and the two
next yrare 2^+ states. The theory is applicable to more than 90% of the nuclei
which have tabulated measurements. The data set of the calculated properties of
1712 even-even nuclei, including spectroscopic properties for 1693 of them, are
provided in CEA website and EPAPS repository with this article \cite{epaps}.Comment: 51 pages with 26 Figures and 4 internal tables; this version is
accepted by Physical Review
Source Dimensions in Ultrarelativistic Heavy Ion Collisions
Recent experiments on pion correlations, interpreted as interferometric
measurements of the collision zone, are compared with models that distinguish a
prehadronic phase and a hadronic phase. The models include prehadronic
longitudinal expansion, conversion to hadrons in local kinetic equilibrium, and
rescattering of the produced hadrons. We find that the longitudinal and outward
radii are surprisingly sensitive to the algorithm used for two-body collisions.
The longitudinal radius measured in collisions of 200 GeV/u sulfur nuclei on a
heavy target requires the existence of a prehadronic phase which converts to
the hadronic phase at densities around 0.8-1.0 GeV/fm. The transverse radii
cannot be reproduced without introducing more complex dynamics into the
transverse expansion.Comment: RevTeX 3.0, 28 pages, 6 figures, not included, revised version, major
change is an additional discussion of the classical two-body collision
algorithm, a (compressed) postscript file of the complete paper including
figures can be obtained from Authors or via anonymous ftp at
ftp://ftp_int.phys.washington.edu/pub/herrmann/pisource.ps.
Hanbury-Brown--Twiss Analysis in a Solvable Model
The analysis of meson correlations by Hanbury-Brown--Twiss interferometry is
tested with a simple model of meson production by resonance decay. We derive
conditions which should be satisfied in order to relate the measured momentum
correlation to the classical source size. The Bose correlation effects are
apparent in both the ratio of meson pairs to singles and in the ratio of like
to unlike pairs. With our parameter values, we find that the single particle
distribution is too distorted by the correlation to allow a straightforward
analysis using pair correlation normalized by the singles rates. An analysis
comparing symmetrized to unsymmetrized pairs is more robust, but nonclassical
off-shell effects are important at realistic temperatures.Comment: 21 pages + 9 figures (tarred etc. using uufiles, submitted
separately), REVTeX 3.0, preprint number: DOE/ER/40561-112/INT93-00-3
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