664 research outputs found
Nuclear Breakup of Borromean Nuclei
We study the eikonal model for the nuclear-induced breakup of Borromean
nuclei, using Li11 and He6 as examples. The full eikonal model is difficult to
realize because of six-dimensional integrals, but a number of simplifying
approximations are found to be accurate. The integrated diffractive and
one-nucleon stripping cross sections are rather insensitive to the
neutron-neutron correlation, but the two-nucleon stripping does show some
dependence on the correlation. The distribution of excitation energy in the
neutron-core final state in one-neutron stripping reactions is quite sensitive
to the shell structure of the halo wave function. Experimental data favor
models with comparable amounts of s- and p-wave in the Li11 halo.Comment: 34 pages REVTeX, 14 postscript figures. Small changes in comparison
with experimen
Estimating monthly-averaged air-sea transfers of heat and momentum using the bulk aerodynamic method
Air-sea transfers of sensible heat, latent heat, and momentum are computed from twenty-five years of middle-latitude and subtropical ocean weather ship data in the North Atlantic and North Pacific using the bulk aerodynamic method. The results show that monthly-averaged wind speeds, temperatures, and humidities can be used to estimate the monthly-averaged sensible and latent heat fluxes computed from the bulk aerodynamic equations to within a relative error of approximately 10%. The estimate of monthly-averaged wind stress under the assumption of neutral stability are shown to be within approximately 5% of the monthly-averaged non-neutral values
Analysis of the surface heat balance over the world ocean
It is possible to estimate long term monthly mean latent and sensible heat fluxes over the ocean to within or approximately 20% relative accuracy of the bulk aerodynamic formulas, by using observations of the monthly mean surface wind speed and the monthly mean sea air temperature and humidity differences. It is possible to make an estimate of the fluxes on a month to month basis from monthly averaged surface data
Charge radius and dipole response of Li
We investigate the consistency of the measured charge radius and dipole
response of Li within a three-body model. We show how these observables
are related to the mean square distance between the Li core and the center
of mass of the two valence neutrons. In this representation we find by
considering the effect of smaller corrections that the discrepancy between the
results of the two measurements is of the order of 1.5. We also
investigate the sensitivity to the three-body structure of Li and find
that the charge radius measurement favors a model with a 50% s-wave component
in the ground state of the two-neutron halo, whereas the dipole response is
consistent with a smaller s-wave component of about 25% value.Comment: 6 pages, 3 figure
Fusion at deep subbarrier energies: potential inversion revisited
For a single potential barrier, the barrier penetrability can be inverted
based on the WKB approximation to yield the barrier thickness. We apply this
method to heavy-ion fusion reactions at energies well below the Coulomb barrier
and directly determine the inter-nucleus potential between the colliding
nuclei. To this end, we assume that fusion cross sections at deep subbarrier
energies are governed by the lowest barrier in the barrier distribution. The
inverted inter-nucleus potentials for the O +Sm and O
+Pb reactions show that they are much thicker than phenomenological
potentials. We discuss a consequence of such thick potential by fitting the
inverted potentials with the Bass function.Comment: 8 pages, 5 figures. Uses aipxfm.sty. A talk given at the FUSION08:
New Aspects of Heavy Ion Collisions Near the Coulomb Barrier, September
22-26, 2008, Chicago, US
Signature of Shallow Potentials in Deep Sub-barrier Fusion Reactions
We extend a recent study that explained the steep falloff in the fusion cross
section at energies far below the Coulomb barrier for the symmetric dinuclear
system 64Ni+64Ni to another symmetric system, 58Ni+58Ni, and the asymmetric
system 64Ni+100Mo. In this scheme the very sensitive dependence of the internal
part of the nuclear potential on the nuclear equation of state determines a
reduction of the classically allowed region for overlapping configurations and
consequently a decrease in the fusion cross sections at bombarding energies far
below the barrier. Within the coupled-channels method, including couplings to
the low-lying 2+ and 3- states in both target and projectile as well as mutual
and two-phonon excitations of these states, we calculate and compare with the
experimental fusion cross sections, S-factors, and logarithmic derivatives for
the above mentioned systems and find good agreement with the data even at the
lowest energies. We predict, in particular, a distinct double peaking in the
S-factor for the far subbarrier fusion of 58Ni+58Ni which should be tested
experimentally.Comment: 34 pages, 10 figures, to appear in Phys. Rev.
Exact Stochastic Mean-Field dynamics
The exact evolution of a system coupled to a complex environment can be
described by a stochastic mean-field evolution of the reduced system density.
The formalism developed in Ref. [D.Lacroix, Phys. Rev. E77, 041126 (2008)] is
illustrated in the Caldeira-Leggett model where a harmonic oscillator is
coupled to a bath of harmonic oscillators. Similar exact reformulation could be
used to extend mean-field transport theories in Many-body systems and
incorporate two-body correlations beyond the mean-field one. The connection
between open quantum system and closed many-body problem is discussed.Comment: Proceedings series of Proceedings of "FUSION08: New Aspects of Heavy
Ion Collisions near the Coulomb Barrier", September 22-26, 2008, Chicago, US
Recent developments in the eikonal description of the breakup of exotic nuclei
The study of exotic nuclear structures, such as halo nuclei, is usually
performed through nuclear reactions. An accurate reaction model coupled to a
realistic description of the projectile is needed to correctly interpret
experimental data. In this contribution, we briefly summarise the assumptions
made within the modelling of reactions involving halo nuclei. We describe
briefly the Continuum-Discretised Coupled Channel method (CDCC) and the
Dynamical Eikonal Approximation (DEA) in particular and present a comparison
between them for the breakup of 15C on Pb at 68AMeV. We show the problem faced
by the models based on the eikonal approximation at low energy and detail a
correction that enables their extension down to lower beam energies. A new
reaction observable is also presented. It consists of the ratio between angular
distributions for two different processes, such as elastic scattering and
breakup. This ratio is completely independent of the reaction mechanism and
hence is more sensitive to the projectile structure than usual reaction
observables, which makes it a very powerful tool to study exotic structures far
from stability.Comment: Contribution to the proceedings of the XXI International School on
Nuclear Physics and Applications & the International Symposium on Exotic
Nuclei, dedicated to the 60th Anniversary of the JINR (Dubna) (Varna,
Bulgaria, 6-12 September 2015), 7 pages, 4 figure
Extraction of nucleus-nucleus potential and energy dissipation from dynamical mean-field theory
Nucleus-nucleus interaction potentials in heavy-ion fusion reactions are
extracted from the microscopic time-dependent Hartree-Fock theory. When the
center-of-mass energy is much higher than the Coulomb barrier energy, extracted
potentials identify with the frozen density approximation. As the
center-of-mass energy decreases to the Coulomb barrier energy, potentials
become energy dependent. This dependence indicates dynamical reorganization of
internal degrees of freedom and leads to a reduction of the "apparent" barrier.
Including this effect leads to the Coulomb barrier energy very close to
experimental one. Aspects of one-body energy dissipation extracted from the
mean-field theory are discussed.Comment: 6 pages, 5 figures. Uses aipxfm.sty. A talk given at the FUSION08:
New Aspects of Heavy Ion Collisions Near the Coulomb Barrier, September
22-26, 2008, Chicago, US
- …