1,806 research outputs found
Coupled-channels density-matrix approach to low-energy nuclear reaction dynamics
Atomic nuclei are complex, quantum many-body systems whose structure
manifests itself through intrinsic quantum states associated with different
excitation modes or degrees of freedom. Collective modes (vibration and/or
rotation) dominate at low energy (near the ground-state). The associated states
are usually employed, within a truncated model space, as a basis in (coherent)
coupled channels approaches to low-energy reaction dynamics. However, excluded
states can be essential, and their effects on the open (nuclear) system
dynamics are usually treated through complex potentials. Is this a complete
description of open system dynamics? Does it include effects of quantum
decoherence? Can decoherence be manifested in reaction observables? In this
contribution, I discuss these issues and the main ideas of a coupled-channels
density-matrix approach that makes it possible to quantify the role and
importance of quantum decoherence in low-energy nuclear reaction dynamics.
Topical applications, which refer to understanding the astrophysically
important collision C + C and achieving a unified quantum
dynamical description of relevant reaction processes of weakly-bound nuclei,
are highlighted.Comment: Invited Talk at FINUSTAR3, August 23-27, 2010, Rhodes, Greece. To be
published in AIP Conference Proceeding
Dynamical collective potential energy landscape: its impact on the competition between fusion and quasi-fission in a heavy fusing system
A realistic microscopically-based quantum approach to the competition between
fusion and quasi-fission in a heavy fusing system is applied to several
reactions leading to No. Fusion and quasi-fission are described in
terms of a diffusion process of nuclear shapes through a dynamical collective
potential energy landscape which is initially diabatic and gradually becomes
adiabatic. The microscopic ingredients of the theory are obtained with a
realistic two-center shell model based on Woods-Saxon potentials. The results
indicate that (i) the diabatic effects play a very important role in the onset
of fusion hindrance for heavy systems, and (ii) very asymmetric reactions
induced by closed shell nuclei seem to be the best suited to synthesize the
heaviest compound nuclei.Comment: 6 pages, 5 figures, To be published in the AIP Proceedings of
FUSION06, International Conference on Reaction Mechanisms and Nuclear
Structure at the Coulomb barrier, March 19-23, 2006, San Servolo (Venice),
Ital
PLATYPUS: a code for fusion and breakup in reactions induced by weakly-bound nuclei within a classical trajectory model with stochastic breakup
A self-contained Fortran-90 program based on a classical trajectory model
with stochastic breakup is presented, which should be a powerful tool for
quantifying complete and incomplete fusion, and breakup in reactions induced by
weakly-bound two-body projectiles near the Coulomb barrier. The code calculates
complete and incomplete fusion cross sections and their angular momentum
distribution, as well as breakup observables (angle, kinetic energy and
relative energy distributions).Comment: Accepted in Computer Physics Communications (2011
Modelling incomplete fusion dynamics of weakly-bound nuclei at near-barrier energies
The classical dynamical model for reactions induced by weakly-bound nuclei at
near-barrier energies is developed further. It allows a quantitative study of
the role and importance of incomplete fusion dynamics in asymptotic
observables, such as the population of high-spin states in reaction products as
well as the angular distribution of direct alpha-production. Model calculations
indicate that incomplete fusion is an effective mechanism for populating
high-spin states, and its contribution to the direct alpha production yield
diminishes with decreasing energy towards the Coulomb barrier. It also becomes
notably separated in angles from the contribution of no-capture breakup events.
This should facilitate the experimental disentanglement of these competing
reaction processes.Comment: 12 pages, 7 figures (for better resolution figures please contact the
author), Accepted in Journal of Physics
Characterizing the astrophysical S-factor for C+C with wave-packet dynamics
A quantitative study of the astrophysically important sub-barrier fusion of
C+C is presented. Low-energy collisions are described in the
body-fixed reference frame using wave-packet dynamics within a nuclear
molecular picture. A collective Hamiltonian drives the time propagation of the
wave-packet through the collective potential-energy landscape. The fusion
imaginary potential for specific dinuclear configurations is crucial for
understanding the appearance of resonances in the fusion cross section. The
theoretical sub-barrier fusion cross sections explain some observed resonant
structures in the astrophysical S-factor. These cross sections monotonically
decline towards stellar energies. The structures in the data that are not
explained are possibly due to cluster effects in the nuclear molecule, which
are to be included in the present approach.Comment: Submitted to Physical Review C; 7 figure
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