1,692 research outputs found
Fusion and breakup in the reactions of 6,7Li and 9Be
We develop a three body classical trajectory Monte Carlo (CTMC) method to
dicsuss the effect of the breakup process on heavy-ion fusion reactions induced
by weakly bound nuclei. This method follows the classical trajectories of
breakup fragments after the breakup takes place, and thus provides an
unambiguous separation between complete and incomplete fusion cross sections.
Applying this method to the fusion reaction Li + Bi, we find that
there is a significant contribution to the total complete fusion cross sections
from the process where all the breakup fragments are captured by the target
nucleus (i.e., the breakup followed by complete fusion).Comment: 4 pages, 3 eps figures. Uses espcrc1.sty. To be published in the
proceedings of the 8th international conference on clustering aspects of
nuclear structure and dynamics, November 24 - 29, 2003, Nara, Japan (Nucl.
Phys. A
Validity of the linear coupling approximation in heavy-ion fusion reactions at sub barrier energies
The role of higher order coupling of surface vibrations to the relative
motion in heavy-ion fusion reactions at near-barrier energies is investigated.
The coupled channels equations are solved to all orders, and also in the linear
and the quadratic coupling approximations. Taking Ni + Zr
reactions as examples, it is shown that all order couplings lead to
considerably improved agreement with the experimentally measured fusion cross
sections and average angular momenta of the compound nucleus for such heavy
nearly symmetric systems. The importance of higher order coupling is also
examined for asymmetric systems like O + Cd, Sm, for
which previous calculations of the fusion cross section seemed to indicate that
the linear coupling approximation was adequate. It is shown that the shape of
the barrier distributions and the energy dependence of the average angular
momentum can change significantly when the higher order couplings are included,
even for systems where measured fusion cross sections may seem to be well
reproduced by the linear coupling approximation.Comment: Latex file, 15 pages, 6 figure
Suppression of complete fusion due to breakup in the reactions B + Bi
Above-barrier cross sections of -active heavy reaction products, as
well as fission, were measured for the reactions of B with
Bi. Detailed analysis showed that the heavy products include components
from incomplete fusion as well as complete fusion (CF), but fission originates
almost exclusively from CF. Compared with fusion calculations without breakup,
the CF cross sections are suppressed by 15% for B and 7% for B. A
consistent and systematic variation of the suppression of CF for reactions of
the weakly bound nuclei Li, Be, B on targets of
Pb and Bi is found as a function of the breakup threshold
energy
Microscopic study of the effect of intrinsic degrees of freedom on fusion
Fusion cross-sections are computed for the CaCa system over a
wide energy range with two microscopic approaches where the only
phenomenological input is the Skyrme energy density functional. The first
method is based on the coupled-channels formalism, using the bare
nucleus-nucleus potential calculated with the frozen Hartree-Fock technique and
the deformation parameters of vibrational states computed with the
time-dependent Hartree-Fock (TDHF) approach. The second method is based on the
density-constrained TDHF method to generate nucleus-nucleus potentials from
TDHF evolution. Both approaches incorporate the effect of couplings to internal
degrees of freedoms in different ways. The predictions are in relatively good
agreement with experimental data.Comment: 6 pages, 11 figures. Invited talk to FUSION1
Statistical model of the powder flow regulation by nanomaterials
Fine powders often tend to agglomerate due to van der Waals forces between
the particles. These forces can be reduced significantly by covering the
particles with nanoscaled adsorbates, as shown by recent experiments. In the
present work a quantitative statistical analysis of the effect of powder flow
regulating nanomaterials on the adhesive forces in powders is given. Covering
two spherical powder particles randomly with nanoadsorbates we compute the
decrease of the mutual van der Waals force. The dependence of the force on the
relative surface coverage obeys a scaling form which is independent of the used
materials. The predictions by our simulations are compared to the experimental
results.Comment: 18 pages, 9 figures, 1 table, LaTeX; reviewed version with minor
changes, published (Powder Technology
Relating breakup and incomplete fusion of weakly-bound nuclei through a classical trajectory model with stochastic breakup
A classical dynamical model that treats break-up stochastically is presented
for low energy reactions of weakly-bound nuclei. The three-dimensional model
allows a consistent calculation of breakup, incomplete and complete fusion
cross sections. The model is assessed by comparing the breakup observables with
CDCC quantum mechanical predictions, which are found to be in reasonable
agreement. Through the model, it is demonstrated that the breakup probability
of the projectile as a function of its distance from the target is of primary
importance for understanding complete and incomplete fusion at energies near
the Coulomb barrier.Comment: Accepted in Physical Review Letter
Importance of Non-Linear Couplings in Fusion Barrier Distributions and Mean Angular Momenta
The effects of higher order coupling of surface vibrations to the relative
motion on heavy-ion fusion reactions at near-barrier energies are investigated.
The coupled channels equations are solved to all orders, and also in the linear
and the quadratic coupling approximations. It is shown that the shape of fusion
barrier distributions and the energy dependence of the average angular momentum
of the compound nucleus can significantly change when the higher order
couplings are included. The role of octupole vibrational excitation of ^{16}O
in the ^{16}O + ^{144}Sm fusion reaction is also discussed using the all order
coupled-channels equations.Comment: 8 pages, 6 figures, To be published in the Proceedings of the FUSION
97 Conference, South Durras, Australia, March 1997 (J. Phys. G
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