1,669 research outputs found
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.
Self-Similar Intermediate Asymptotics for a Degenerate Parabolic Filtration-Absorption Equation
The equation is
known in literature as a qualitative mathematical model of some biological
phenomena. Here this equation is derived as a model of the groundwater flow in
a water absorbing fissurized porous rock, therefore we refer to this equation
as a filtration-absorption equation. A family of self-similar solutions to this
equation is constructed. Numerical investigation of the evolution of
non-self-similar solutions to the Cauchy problems having compactly supported
initial conditions is performed. Numerical experiments indicate that the
self-similar solutions obtained represent intermediate asymptotics of a wider
class of solutions when the influence of details of the initial conditions
disappears but the solution is still far from the ultimate state: identical
zero. An open problem caused by the nonuniqueness of the solution of the Cauchy
problem is discussed.Comment: 19 pages, includes 7 figure
Shell Model Monte Carlo Studies of -Soft Nuclei
We present Shell Model Monte Carlo calculations for nuclei within the full
major shell 50-82 for both protons and neutrons. The interaction is determined
solely by self-consistency and odd-even mass differences. The methods are
illustrated for Sn, Te and Xe. We calculate shape
distributions, moments of inertia and pairing correlations as functions of
temperature and angular velocity. Our calculations are the first microscopic
evidence of -softness of nuclei in this region.Comment: uuencoded postscript of manuscript with three figure
Nuclear composition and energy spectra in the 12 April 1969 solar particle event
Nuclear composition for several multicharged nuclei and energy spectra for hydrogen, helium, and medium nuclei measured in solar particle even
Fitting theories of nuclear binding energies
In developing theories of nuclear binding energy such as density-functional
theory, the effort required to make a fit can be daunting due to the large
number of parameters that may be in the theory and the large number of nuclei
in the mass table. For theories based on the Skyrme interaction, the effort can
be reduced considerably by using the singular value decomposition to reduce the
size of the parameter space. We find that the sensitive parameters define a
space of dimension four or so, and within this space a linear refit is adequate
for a number of Skyrme parameters sets from the literature. We do not find
marked differences in the quality of the fit between the SLy4, the Bky4 and SkP
parameter sets. The r.m.s. residual error in even-even nuclei is about 1.5 MeV,
half the value of the liquid drop model. We also discuss an alternative norm
for evaluating mass fits, the Chebyshev norm. It focuses attention on the cases
with the largest discrepancies between theory and experiment. We show how it
works with the liquid drop model and make some applications to models based on
Skyrme energy functionals. The Chebyshev norm seems to be more sensitive to new
experimental data than the root-mean-square norm. The method also has the
advantage that candidate improvements to the theories can be assessed with
computations on smaller sets of nuclei.Comment: 17 pages and 4 figures--version encorporates referee's comment
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
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.
Absorption of Energy at a Metallic Surface due to a Normal Electric Field
The effect of an oscillating electric field normal to a metallic surface may
be described by an effective potential. This induced potential is calculated
using semiclassical variants of the random phase approximation (RPA). Results
are obtained for both ballistic and diffusive electron motion, and for two and
three dimensional systems. The potential induced within the surface causes
absorption of energy. The results are applied to the absorption of radiation by
small metal spheres and discs. They improve upon an earlier treatment which
used the Thomas-Fermi approximation for the effective potential.Comment: 19 pages (Plain TeX), 2 figures, 1 table (Postscript
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