27 research outputs found
Hindrance of ^{16}O+^{208}Pb fusion at extreme sub-barrier energies
We analyze the fusion data for O+Pb using coupled-channels
calculations. We include couplings to the low-lying surface excitations of the
projectile and target and study the effect of the (O,O)
one-neutron pickup. The hindrance of the fusion data that is observed at
energies far below the Coulomb barrier cannot be explained by a conventional
ion-ion potential and defining the fusion in terms of ingoing-wave boundary
conditions (IWBC). We show that the hindrance can be explained fairly well by
applying the M3Y double-folding potential which has been corrected with a
calibrated, repulsive term that simulates the effect of nuclear
incompressibility.
We show that the coupling to one-neutron transfer channels plays a crucial
role in improving the fit to the data. The best fit is achieved by increasing
the transfer strength by 25% relative to the strength that is required to
reproduce the one-neutron transfer data. The larger strength is not unrealistic
because the calculated inelastic plus transfer cross section is in good
agreement with the measured quasielastic cross section. We finally discuss the
problem of reproducing the fusion data at energies far above the Coulomb
barrier. Here we do not account for the data when we apply the IWBC but the
discrepancy is essentially eliminated by applying the M3Y+repulsion potential
and a weak, short-ranged imaginary potential.Comment: text and 8 fifure
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
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
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
Coupled-Channels Approach for Dissipative Quantum Dynamics in Near-Barrier Collisions
A novel quantum dynamical model based on the dissipative quantum dynamics of
open quantum systems is presented. It allows the treatment of both
deep-inelastic processes and quantum tunneling (fusion) within a fully quantum
mechanical coupled-channels approach. Model calculations show the transition
from pure state (coherent) to mixed state (decoherent and dissipative) dynamics
during a near-barrier nuclear collision. Energy dissipation, due to
irreversible decay of giant-dipole excitations of the interacting nuclei,
results in hindrance of quantum tunneling.Comment: 8 pages, 4 figures, Invited talk by A. Diaz-Torres at the FUSION08
Conference, Chicago, September 22-26, 2008, To appear in AIP Conference
Proceeding
Mass Distributions Beyond TDHF
The mass distributions for giant dipole resonances in 32S and 132Sn decaying
through particle emission and for deep-inelastic collisions between 16O nuclei
have been investigated by implementing the Balian-Veneroni variational
technique based upon a three-dimensional time-dependent Hartree-Fock code with
realistic Skyrme interactions. The mass distributions obtained have been shown
to be significantly larger than the standard TDHF results.Comment: 6 pages, 2 figures, Based on talk by J. M. A. Broomfield at the
FUSION08 Conference, Chicago, September 22-26, 2008. Conference proceedings
to be published by AI
Decay Rate of Triaxially-Deformed Proton Emitters
The decay rate of a triaxially-deformed proton emitter is calculated in a
particle-rotor model, which is based on a deformed Woods-Saxon potential and
includes a deformed spin-orbit interaction. The wave function of the
ground state of the deformed proton emitter Ho is obtained
in the adiabatic limit, and a Green's function technique is used to calculate
the decay rate and branching ratio to the first excited 2 state of the
daughter nucleus. Only for values of the triaxial angle
is good agreement obtained for both the total decay rate and the 2
branching ratio.Comment: 19 pages, 4 figure