874 research outputs found
Multipole Expansion for Relativistic Coulomb Excitation
We derive a general expression for the multipole expansion of the
electro-magnetic interaction in relativistic heavy-ion collisions, which can be
employed in higher-order dynamical calculations of Coulomb excitation. The
interaction has diagonal as well as off-diagonal multipole components,
associated with the intrinsic and relative coordinates of projectile and
target. A simple truncation in the off-diagonal components gives excellent
results in first-order perturbation theory for distant collisions and for beam
energies up to 200 MeV/nucleon.Comment: 3 figures, Accepted for publication in Phys. Rev.
Sensitivity to multi-phonon excitations in heavy-ion fusion reactions
Measured cross sections for the fusion of {64}Ni with {64}Ni, {74}Ge, and
{100}Mo targets are analyzed in a coupled-channels approach. The data for the
{64}Ni target above 0.1 mb are reproduced by including couplings to the
low-lying 2^+ and 3^- states and the mutual and two-phonon excitations of these
states. The calculations become more challenging as the fusing nuclei become
softer and heavier, and excitations to multi-phonon states start to play an
increasingly important role. Thus it is necessary to include up to four-phonon
excitations in order to reproduce the data for the {64}Ni+{74}Ge system.
Similar calculations for {64}Ni+{100}Mo, and also for the symmetric
{74}Ge+{74}Ge system, show large discrepancies with the data. Possible ways to
improve the calculations are discussed.Comment: 24 pages, 7 figures, 4 table
Hindrance of heavy-ion fusion due to nuclear incompressibility
We propose a new mechanism to explain the unexpected steep falloff of fusion
cross sections at energies far below the Coulomb barrier. The saturation
properties of nuclear matter are causing a hindrance to large overlap of the
reacting nuclei and consequently a sensitive change of the nuclear potential
inside the barrier. We report in this letter a good agreement with the data of
coupled-channels calculation for the {64}Ni+{64}Ni combination using the
double-folding potential with M3Y-Reid effective N-N forces supplemented with a
repulsive core that reproduces the nuclear incompressibility for total overlap.Comment: 4 pages, 3 figure
A non-perturbative approach to halo breakup
The theory of weakly bound cluster breakup, like halo nucleus breakup, needs
an accurate treatment of the transitions from bound to continuum states induced
by the nuclear and Coulomb potentials. When the transition probability is not
very small, a non-perturbative framework might be necessary. Nuclear excitation
dominates at small impact parameters whereas the Coulomb potential being long
range acts over a larger impact parameter interval. In this article, we propose
an effective breakup amplitude which meets a number of requirements necessary
for an accurate quantitative description of the breakup reaction mechanism.
Furthermore our treatment gives some insight on the interplay between time
dependent perturbation theory and sudden approximation and it allows to include
the nuclear and Coulomb potentials to all orders within an eikonal-like
framework.Comment: 22 Latex pages, 1 table, 8 eps figures. Accepted for publication on
Nucl. Phys.
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.
Dynamical deformation effects in subbarrier fusion of Ni+Sn
We show that dynamical deformation effects play an important role in fusion
reactions involving the Ni nucleus, in particular the
Ni+Sn system. We calculate fully microscopic interaction
potentials and the corresponding subbarrier fusion cross sections.Comment: 3 pages, 2 figure
Nuclear pairing and Coriolis effects in proton emitters
We introduce a Hartree-Fock-Bogoliubov mean-field approach to treat the
problem of proton emission from a deformed nucleus. By substituting a rigid
rotor in a particle-rotor-model with a mean-field we obtain a better
description of experimental data in Ho. The approach also elucidates
the softening of kinematic coupling between particle and collective rotation,
the Coriolis attenuation problem.Comment: 2 pages, 1 figur
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