74 research outputs found
Microscopic mass estimations
The quest to build a mass formula which have in it the most relevant
microscopic contributions is analyzed. Inspired in the successful Duflo-Zuker
mass description, the challenges to describe the shell closures in a more
transparent but equally powerful formalism are discussed.Comment: 14 pages, 6 figures, submitted to Journal of Physics G, Focus issue
on Open Problems in Nuclear Structure Theor
How good are the Garvey-Kelson predictions of nuclear masses?
The Garvey-Kelson relations are used in an iterative process to predict
nuclear masses in the neighborhood of nuclei with measured masses. Average
errors in the predicted masses for the first three iteration shells are smaller
than those obtained with the best nuclear mass models. Their quality is
comparable with the Audi-Wapstra extrapolations, offering a simple and
reproducible procedure for short range mass predictions. A systematic study of
the way the error grows as a function of the iteration and the distance to the
known masses region, shows that a correlation exists between the error and the
residual neutron-proton interaction, produced mainly by the implicit assumption
that varies smoothly along the nuclear landscape.Comment: 10 pages, 18 figure
NUCLEAR MASSES AND THEIR IMPACT IN R-PROCESS NUCLEOSYNTHESIS
During the present Thesis, the role of the nuclear masses in r-process nucleosynthesis
calculations have been explored. In order to accomplish this goal, we have computed
neutron capture rates in the framework of the statistical model for all relevant nuclei
in the r-process regime, to be more specific, nuclei ranging from Zn (Z=30) to Bi (Z=83)
and contained inside the model dependent driplines. We have use the currently available
mass models that best reproduce the known masses with a root mean square deviation
smaller than RMSD<600 keV. This include the following set of mass models: Finite Range
Droplet Model (FRDM), Weizsäcker-Skyrme model (WS3) and two variants of
the Duflo-Zuker mass model, namely DZ10 and DZ31. The thermodynamical conditions were taken from hydrodynamical simulations corresponding to high entropy neutrino winds from core collapse supernovae (SNe) and Neutron star mergers(NSM)
On the nuclear robustness of the r process in neutron-star mergers
We have performed r-process calculations for matter ejected dynamically in
neutron star mergers based on a complete set of trajectories from a
three-dimensional relativistic smoothed particle hydrodynamic simulation. Our
calculations consider an extended nuclear network, including spontaneous,
- and neutron-induced fission and adopting fission yield distributions
from the ABLA code. We have studied the sensitivity of the r-process abundances
to nuclear masses by using different models. Most of the trajectories,
corresponding to 90% of the ejected mass, follow a relatively slow expansion
allowing for all neutrons to be captured. The resulting abundances are very
similar to each other and reproduce the general features of the observed
r-process abundance (the second and third peaks, the rare-earth peak and the
lead peak) for all mass models as they are mainly determined by the fission
yields. We find distinct differences in the abundance yields at and just above
the third peak, which can be traced back to different predictions of neutron
separation energies for r-process nuclei around neutron number . The
remaining trajectories, which contribute 10% by mass to the total integrated
abundances, follow such a fast expansion that the r process does not use all
the neutrons. This also leads to a larger variation of abundances among
trajectories as fission does not dominate the r-process dynamics. The total
integrated abundances are dominated by contributions from the slow abundances
and hence reproduce the general features of the observed r-process abundances.
We find that at timescales of weeks relevant for kilonova light curve
calculations, the abundance of actinides is larger than the one of lanthanides.
Hence actinides can be even more important than lanthanides to determine the
photon opacities under kilonova conditions. (Abridged)Comment: 17 pages, 7 figures, resubmitted to PRC addressing referee comment
The anatomy of the simplest Duflo-Zuker mass formula
The simplest version of the Duflo-Zuker mass model (due entirely to the late
Jean Duflo) is described by following step by step the published computer code.
The model contains six macroscopic monopole terms leading asymptotically to a
Liquid Drop form, three microscopic terms supposed to mock configuration mixing
(multipole) corrections to the monopole shell effects, and one term in charge
of detecting deformed nuclei and calculating their masses. A careful analysis
of the model suggests a program of future developments that includes a
complementary approach to masses based on an independently determined monopole
Hamiltonian, a better description of deformations and specific suggestions for
the treatment of three body forces.Comment: 30 pages, 21 figures, extensives changes to improve presentation and
clarity, with an ample discussion of the anomalous term. Accepted for
publication in Nuclear Physics
Behavior of early warnings near the critical temperature in the two-dimensional Ising model
Among the properties that are common to complex systems, the presence of
critical thresholds in the dynamics of the system is one of the most important.
Recently, there has been interest in the universalities that occur in the
behavior of systems near critical points. These universal properties make it
possible to estimate how far a system is from a critical threshold. Several
early-warning signals have been reported in time series representing systems
near catastrophic shifts. The proper understanding of these early-warnings may
allow the prediction and perhaps control of these dramatic shifts in a wide
variety of systems. In this paper we analyze this universal behavior for a
system that is a paradigm of phase transitions, the Ising model. We study the
behavior of the early-warning signals and the way the temporal correlations of
the system increase when the system is near the critical point.Comment: 20 pages, 8 figures, Submitted to PLOS ONE on Oct. 20th 2014.
PONE-D-14-4718
Nuclear masses and the number of valence nucleons
An improved version of the liquid drop model is presented. The addition of two terms, linear and quadratic in the total number of valence nucleons (particles or holes), improves the description of atomic masses, which can be fitted with an r.m.s. error of 1.2 MeV. Predictions are analysed an compared with those of established models. (c) 2007 Elsevier B.V. All rights reserved
Image reconstruction techniques applied to nuclear mass models
A new procedure is presented that combines well-known nuclear models with image reconstruction techniques. A color-coded image is built by taking the differences between measured masses and the predictions given by the different theoretical models. This image is viewed as part of a larger array in the (N,Z) plane, where unknown nuclear masses are hidden, covered by a "mask." We apply a suitably adapted deconvolution algorithm, used in astronomical observations, to "open the window" and see the rest of the pattern. We show that it is possible to improve significantly mass predictions in regions not too far from measured nuclear masses
Symmetry Energy I: Semi-Infinite Matter
Energy for a nucleus is considered in macroscopic limit, in terms of nucleon
numbers. Further considered for a nuclear system is the Hohenberg-Kohn energy
functional, in terms of proton and neutron densities. Finally,
Skyrme-Hartree-Fock calculations are carried out for a half-infinite
particle-stable nuclear-matter. In each case, the attention is focused on the
role of neutron-proton asymmetry and on the nuclear symmetry energy. We extend
the considerations on the symmetry term from an energy formula to the
respective term in the Hohenberg-Kohn functional. We show, in particular, that
in the limit of an analytic functional, and subject to possible Coulomb
corrections, it is possible to construct isoscalar and isovector densities out
of the proton and neutron densities, that retain a universal relation to each
other, approximately independent of asymmetry. In the so-called local
approximation, the isovector density is inversely proportional to the symmetry
energy in uniform matter at the local isoscalar density. Generalized symmetry
coefficient of a nuclear system is related, in the analytic limit of a
functional, to an integral of the isovector density. We test the relations,
inferred from the Hohenberg-Kohn functional, in the Skyrme-Hartree-Fock
calculations of half-infinite matter. Within the calculations, we obtain
surface symmetry coefficients and parameters characterizing the densities, for
the majority of Skyrme parameterizations proposed in the literature. The
volume-to-surface symmetry-coefficient ratio and the displacement of nuclear
isovector relative to isoscalar surfaces both strongly increase as the slope of
symmetry energy in the vicinity of normal density increases.Comment: 87 pages, 18 figures; discussion of Kohn-Sham method added,
comparison to results in literature broadene
The beta-Oslo method: experimentally constrained () reaction rates relevant to the -process
Unknown neutron-capture reaction rates remain a significant source of
uncertainty in state-of-the-art -process nucleosynthesis reaction network
calculations. As the -process involves highly neutron-rich nuclei for which
direct () cross-section measurements are virtually impossible,
indirect methods are called for to constrain () cross sections used
as input for the -process nuclear network. Here we discuss the newly
developed beta-Oslo method, which is capable of providing experimental input
for calculating () rates of neutron-rich nuclei. The beta-Oslo method
represents a first step towards constraining neutron-capture rates of
importance to the -process.Comment: 4 pages, 1 figure, conference proceedings Nuclei in the Cosmos XV
2018, Italy
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