455 research outputs found
Mean free paths and in-medium scattering cross sections of energetic nucleons in neutron-rich nucleonic matter within the relativistic impulse approximation
The mean free paths and in-medium scattering cross sections of energetic
nucleons in neutron-rich nucleonic matter are investigated using the nucleon
optical potential obtained within the relativistic impulse approximation with
the empirical nucleon-nucleon scattering amplitudes and the nuclear densities
obtained in the relativistic mean field model. It is found that the
isospin-splitting of nucleon mean free paths, sensitive to the imaginary part
of the symmetry potential, changes its sign at certain high kinetic energy. The
in-medium nucleon-nucleon cross sections are analytically and numerically
demonstrated to be essentially independent of the isospin asymmetry of the
medium and increase linearly with density in the high energy region where the
relativistic impulse approximation is applicable.Comment: 13 pages, 6 figure
Implications of Variability Patterns observed in TeV Blazars on the Structure of the Inner Jet
The recent long look X-ray observations of TeV blazars have revealed many
important new features concerning their time variability. In this paper, we
suggest a physical interpretation for those features based on the framework of
the internal and external shock scenarios. We present a simplified model
applicable to TeV blazars, and investigate through simulations how each of the
model parameters would affect to the observed light curve or spectrum. In
particular, we show that the internal shock scenario naturally leads to all the
observed variability properties including the structure function, but for it to
be applicable, the fractional fluctuation of the initial bulk Lorentz factors
must be small, with sigma_gamma / gamma_average < 0.01. This implies very low
dynamical efficiency of the internal shock scenario. We also suggest that
several observational quantities -- such as the characteristic time scale, the
relative amplitude of flares as compared to the steady (``offset'') component,
and the slope of the structure function -- can be used to probe the inner jet.
The results are applied to the TeV blazar Mrk421, and this, within the context
of the model, leads to the determination of several physical parameters: the
ejection of a shell with average thickness of ~1E13 cm occurs on average every
10 minutes, and the shells collide ~1E17 cm away from the central source.Comment: 12 pages, 13 figures, to appear in Ap
The neutron halo of He in a microscopic model
The two--neutron separation energy of He has been reproduced for the
first time in a realistic parameter--free microscopic multicluster model
comprising the and clusterizations, with cluster
breathing excitations included. The contribution of the channel is
substantial. A very thick (0.85 fm) neutron halo has been found in full
agreement with the results of the latest phenomenological analysis.Comment: Submitted to Phys. Rev. C, 8 pages, Latex with Revtex, 2 figures (not
included) available on request, 08-03-9
Modified Bethe-Weizsacker mass formula with isotonic shift and new driplines
Nuclear masses are calculated using the modified Bethe-Weizsacker mass
formula in which the isotonic shifts have been incorporated. The results are
compared with the improved liquid drop model with isotonic shift. Mass excesses
predicted by this method compares well with the microscopic-macroscopic model
while being much more simple. The neutron and proton drip lines have been
predicted using this modified Bethe-Weizsacker mass formula with isotonic
shifts.Comment: 9 pages including 2 figure
Application of Absorbing Boundary Condition to Nuclear Breakup Reactions
Absorbing boundary condition approach to nuclear breakup reactions is
investigated. A key ingredient of the method is an absorbing potential outside
the physical area, which simulates the outgoing boundary condition for
scattered waves. After discretizing the radial variables, the problem results
in a linear algebraic equation with a sparse coefficient matrix, to which
efficient iterative methods can be applicable. No virtual state such as
discretized continuum channel needs to be introduced in the method. Basic
aspects of the method are discussed by considering a nuclear two-body
scattering problem described with an optical potential. We then apply the
method to the breakup reactions of deuterons described in a three-body direct
reaction model. Results employing the absorbing boundary condition are found to
accurately coincide with those of the existing method which utilizes
discretized continuum channels.Comment: 21 pages, 5 figures, RevTeX
Neutron and proton drip lines using the modified Bethe-Weizsacker mass formula
Proton and neutron separation energies have been calculated using the
extended Bethe-Weizsacker mass formula. This modified Bethe-Weizsacker mass
formula describes minutely the positions of all the old and the new magic
numbers. It accounts for the disappearance of some traditional magic numbers
for neutrons and provides extra stability for some new neutron numbers. The
neutron and proton drip lines have been predicted using this extended
Bethe-Weizsacker mass formula. The implications of the proton drip line on the
astrophysical rp-process and of the neutron drip line on the astrophysical
r-process have been discussed.Comment: 5 pages, 2 figure
Fusion-Fission of 16O+197Au at Sub-Barrier Energies
The recent discovery of heavy-ion fusion hindrance at far sub-barrier
energies has focused much attention on both experimental and theoretical
studies of this phenomenon. Most of the experimental evidence comes from
medium-heavy systems such as Ni+Ni to Zr+Zr, for which the compound system
decays primarily by charged-particle evaporation. In order to study heavier
systems, it is, however, necessary to measure also the fraction of the decay
that goes into fission fragments. In the present work we have, therefore,
measured the fission cross section of 16O+197Au down to unprecedented far
sub-barrier energies using a large position sensitive PPAC placed at backward
angles. The preliminary cross sections will be discussed and compared to
earlier studies at near-barrier energies. No conclusive evidence for
sub-barrier hindrance was found, probably because the measurements were not
extended to sufficiently low energies.Comment: Fusion06 - Intl. Conf. on Reaction Mechanisms and Nuclear Structure
at the Coulomb Barrier, San Servolo, Venezia, Italy, March 19-223, 2006 5
pages, 4 figure
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