997 research outputs found
Macroscopic Features of Light Heavy-Ion Fission Reactions
Global macroscopic features observed in the fully-damped binary processes in
light di-nuclear systems, such as limiting angular momenta, mean total kinetic
energies and energy thresholds for fusion-fission processes (''fission
thresholds") are presented. Their deduced systematics are consistent with that
obtained for heavier systems and follow a fusion-fission picture which can be
described by a realistic rotating liquid drop model considering diffuse-surface
and finite-nuclear-range effects.Comment: 8 pages(REVTeX), 3 figures available upon request, to appear in Phys.
Rev.
Binary Decay of Light Nuclear Systems
A review of the characteristic features found in fully energy-damped,
binarydecay yields from light heavy-ion reactions with is presented. The different aspects of these yields that
have been used to support models of compound-nucleus (CN) fission and
deep-inelastic dinucleus orbiting are highlighted. Cross section calculations
based on the statistical phase space at different stages of the reaction are
presented and compared to the experimental results. Although the statistical
models are found to reproduce most of the observed experimental behaviors, an
additional reaction component corresponding to a heavy-ion resonance or
orbiting mechanism is also evident in certain systems. The system dependence of
this second component is discussed. The extent to which the binary yields in
very light systems can be viewed as resulting from a
fusion-fission mechanism is explored. A number of unresolved questions, such as
whether the different observed behaviors reflect characteristically different
reaction times, are discussed.Comment: 79 pages REVTeX file, 39 ps Figures included - to be publihed in
Physics Report
Entrance-channel Mass-asymmetry Dependence of Compound-nucleus Formation Time in Light Heavy-ion Reactions
The entrance-channel mass-asymmetry dependence of the compound nucleus
formation time in light heavy-ion reactions has been investigated within the
framework of semiclassical dissipative collision models. the model calculations
have been succesfully applied to the formation of the Ar compound
nucleus as populated via the Be+Si, B+Al,
C+Mg and F+F entrance channels. The shape evolution
of several other light composite systems appears to be consistent with the
so-called "Fusion Inhibition Factor" which has been experimentally observed. As
found previously in more massive systems for the fusion-evaporation process,
the entrance-channel mass-asymmetry degree of freedom appears to determine the
competition between the different mechanisms as well as the time scales
involved.Comment: 12 pages, 3 Figures available upon request, Submitted at Phys. Rev.
Study of 9Be+12C elastic scattering at energies near the Coulomb barrier
In this work, angular distribution measurements for the elastic channel were
performed for the 9Be+12C reaction at the energies ELab=13.0, 14.5, 17.3, 19.0
and 21.0 MeV, near the Coulomb barrier. The data have been analyzed in the
framework of the double folding S\~ao Paulo potential. The experimental elastic
scattering angular distributions were well described by the optical potential
at forward angles for all measured energies. However, for the three highest
energies, an enhancement was observed for intermediate and backward angles.
This can be explained by the elastic transfer mechanism.
Keywords: 9Be+12C, Elastic Scattering, S\~aoo Paulo Potential
6Li direct breakup lifetimes
alpha-d coincidence data were studied for the 6Li + 59Co reaction at E(lab) =
29.6 MeV. By using a kinematic analysis, it was possible to identify which
process, leading to the same final state, has the major contribution for each
of the selected angular regions. Contributions of the 6Li sequential and direct
breakup to the incomplete fusion/transfer process were discussed by considering
the lifetimes obtained by using a semiclassical approach, for both breakup
components.Comment: 5 pages, 4 figures, Invited Talk (Parrallel Sessions) of A. Szanto de
Toledo, prepared for the Proccedings of the 10th International Conference on
Nucleus-Nucleus Collisions, August 16-21, 2009, Beijing, China; submitted to
Nucl. Phys. A (Proceedings of NN2009
Dissipative collisions in O + Al at E=116 MeV
The inclusive energy distributions of fragments (3Z7) emitted in
the reaction O + Al at 116 MeV have been measured in
the angular range = 15 - 115. A non-linear
optimisation procedure using multiple Gaussian distribution functions has been
proposed to extract the fusion-fission and deep inelastic components of the
fragment emission from the experimental data. The angular distributions of the
fragments, thus obtained, from the deep inelastic component are found to fall
off faster than those from the fusion-fission component, indicating shorter
life times of the emitting di-nuclear systems. The life times of the
intermediate di-nuclear configurations have been estimated using a diffractive
Regge-pole model. The life times thus extracted (
Sec.) are found to decrease with the increase in the fragment charge. Optimum
Q-values are also found to increase with increasing charge transfer i.e. with
the decrease in fragment charge.Comment: 9 pages, 4 figures, 1 tabl
Towards Quantum Transport for Nuclear Reactions
Nonequilibrium Green's functions represent a promising tool for describing
central nuclear reactions. Even at the single-particle level, though, the
Green's functions contain more information that computers may handle in the
foreseeable future. In this study, we investigate whether all the information
contained in the Green's functions is necessarily relevant when describing the
time evolution of nuclear reactions. For this, we carry out mean-field
calculations of slab collisions in one dimension.Comment: 8 pages, 11 figures, contribution to Proceedings of the Conference on
Frontiers of Quantum and Mesoscopic Thermodynamics, 28 July - 2 August 2008,
Prague, Czech Republi
Near-barrier Fusion and Breakup/Transfer induced by Weakly Bound and Exotic Halo Nuclei
The influence on the fusion process of coupling to collective degrees of
freedom has been explored. The significant enhancement of the fusion cross
section at sub-barrier energies was compared to predictions of one-dimensional
barrier penetration models. This was understood in terms of the dynamical
processes arising from strong couplings to collective inelastic excitations of
the target and projectile. However, in the case of reactions where at least one
of the colliding nuclei has a sufficiently low binding energy, for breakup to
become an important process, conflicting model predictions and experimental
results have been reported in the literature. Excitation functions for sub- and
near-barrier total (complete + incomplete) fusion cross sections have been
measured for the Li+Co reactions. Elastic scattering as well as
breakup/transfer yields have also been measured at several incident energies.
Results of Continuum-Discretized Coupled-Channel ({\sc Cdcc}) calculations
describe reasonably well the experimental data for both reactions at and above
the barrier. A systematic study of He induced fusion reactions with a
three-body {\sc Cdcc} method is presented. The relative importance of breakup
and bound-state structure effects on total fusion (excitation functions) is
particularly investigated. The four-body {\sc Cdcc} model is being currently
developed.Comment: 8 pages, 3 figures; espcrc1 style; Invited Talk given at IX Int.Conf.
on Nucleus-Nucleus Collisions, Rio de Janeiro Aug.2006; submitted to
Nucl.Phys.
- …