2,911 research outputs found
Cluster formations in deformed states for Si and S
We study cluster formation in strongly deformed states for Si and
S using a macroscopic-microscopic model. The study is based on
calculated total-energy surfaces, which are the sums of deformation-dependent
macroscopic-microscopic potential-energy surfaces and rotational-energy
contributions. We analyze the angular-momentum-dependent total-energy surfaces
and identify the normal- and super-deformed states in Si and S,
respectively. We show that at sufficiently high angular momenta strongly
deformed minima appear. The corresponding microscopic density distributions
show cluster structure that closely resemble the O+C and
O+O configurations. At still higher deformations, beyond the
minima, valleys develop in the calculated surfaces. These valleys lead to mass
divisions that correspond to the target-projectile configurations for which
molecular resonance states have been observed. We discuss the relation between
the one-body deformed minima and the two-body molecular-resonance states.Comment: 6 pages, 7 figure
Proton-neutron quadrupole interactions: an effective contribution to the pairing field
We point out that the proton-neutron energy contribution, for low multipoles
(in particular for the quadrupole component), effectively renormalizes the
strength of the pairing interaction acting amongst identical nucleons filling
up a single-j or a set of degenerate many-j shells. We carry out the
calculation in lowest-order perturbation theory. We perform a study of this
correction in various mass regions. These results may have implications for the
use of pairing theory in medium-heavy nuclei and for the study of pairing
energy corrections to the liquid drop model when studying nuclear masses.Comment: 19 pages, TeX, 3 tables, 2 figures. Accepted in PR
Dynamical approach to heavy-ion induced fission using actinide target nuclei at energies around the Coulomb barrier
In order to describe heavy-ion fusion reactions around the Coulomb barrier
with an actinide target nucleus, we propose a model which combines the
coupled-channels approach and a fluctuation-dissipation model for dynamical
calculations. This model takes into account couplings to the collective states
of the interacting nuclei in the penetration of the Coulomb barrier and the
subsequent dynamical evolution of a nuclear shape from the contact
configuration. In the fluctuation-dissipation model with a Langevin equation,
the effect of nuclear orientation at the initial impact on the prolately
deformed target nucleus is considered. Fusion-fission, quasi-fission and deep
quasi-fission are separated as different Langevin trajectories on the potential
energy surface. Using this model, we analyze the experimental data for the mass
distribution of fission fragments (MDFF) in the reactions of
S+U and Si+U at several incident energies
around the Coulomb barrier. We find that the time scale in the quasi-fission as
well as the deformation of fission fragments at the scission point are
different between the Si+U and S+U systems,
causing different mass asymmetries of the quasi-fission.Comment: 11 figure
Changes in r-process abundances at late times
We explore changes in abundance patterns that occur late in the r process. As
the neutrons available for capture begin to disappear, a quasiequilibrium
funnel shifts material into the large peaks at A=130 and A=195, and into the
rare-earth "bump" at A=160. A bit later, after the free-neutron abundance has
dropped and beta-decay has begun to compete seriously with neutron capture, the
peaks can widen. The degree of widening depends largely on neutron-capture
rates near closed neutron shells and relatively close to stability. We identify
particular nuclei the capture rates of which should be examined experimentally,
perhaps at a radioactive beam facility.Comment: 8 pages, 14 figures included in tex
Semiempirical Shell Model Masses with Magic Number Z = 126 for Superheavy Elements
A semiempirical shell model mass equation applicable to superheavy elements
up to Z = 126 is presented and shown to have a high predictive power. The
equation is applied to the recently discovered superheavy nuclei Z = 118, A =
293 and Z = 114, A = 289 and their decay products.Comment: 7 pages, including 2 figures and 2 table
Two-Step Model of Fusion for Synthesis of Superheavy Elements
A new model is proposed for fusion mechanisms of massive nuclear systems
where so-called fusion hindrance exists. The model describes two-body collision
processes in an approaching phase and shape evolutions of an amalgamated system
into the compound nucleus formation. It is applied to Ca-induced
reactions and is found to reproduce the experimental fusion cross sections
extremely well, without any free parameter. Combined with the statistical decay
theory, residue cross sections for the superheavy elements can be readily
calculated. Examples are given.Comment: 4 pages, 4 figure
A new three-loop sum-integral of mass dimension two
We evaluate a new 3-loop sum-integral which contributes to the Debye
screening mass in hot QCD. While we manage to derive all divergences
analytically, its finite part is mapped onto simple integrals and evaluated
numerically.Comment: 15 page
Mean-field description of ground-state properties of drip-line nuclei. (I) Shell-correction method
A shell-correction method is applied to nuclei far from the beta stability
line and its suitability to describe effects of the particle continuum is
discussed. The sensitivity of predicted locations of one- and two-particle drip
lines to details of the macroscopic-microscopic model is analyzed.Comment: 22 REVTeX pages, 13 uuencoded postscript figures available upon
reques
Dependence of direct neutron capture on nuclear-structure models
The prediction of cross sections for nuclei far off stability is crucial in
the field of nuclear astrophysics. We calculate direct neutron capture on the
even-even isotopes Sn and Pb with energy levels,
masses, and nuclear density distributions taken from different
nuclear-structure models. The utilized structure models are a
Hartree-Fock-Bogoliubov model, a relativistic mean field theory, and a
macroscopic-microscopic model based on the finite-range droplet model and a
folded-Yukawa single-particle potential. Due to the differences in the
resulting neutron separation and level energies, the investigated models yield
capture cross sections sometimes differing by orders of magnitude. This may
also lead to differences in the predicted astrophysical r-process paths.
Astrophysical implications are discussed.Comment: 25 pages including 12 figures, RevTeX, to appear in Phys. Rev.
A series of coverings of the regular n-gon
We define an infinite series of translation coverings of Veech's double-n-gon
for odd n greater or equal to 5 which share the same Veech group. Additionally
we give an infinite series of translation coverings with constant Veech group
of a regular n-gon for even n greater or equal to 8. These families give rise
to explicit examples of infinite translation surfaces with lattice Veech group.Comment: A missing case in step 1 in the proof of Thm. 1 b was added. (To
appear in Geometriae Dedicata.
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