245 research outputs found
Natural Units For Nuclear Energy Density Functional Theory
Naive dimensional analysis based on chiral effective theory, when adapted to
nuclear energy density functionals, prescribes natural units and a hierarchy of
contributions that could be used to constrain fits of generalized functionals.
By applying these units, a large sample of Skyrme parametrizations is examined
for naturalness, which is signaled by dimensionless coupling constants of order
one. The bulk of the parameters are found to be natural, with an underlying
scale consistent with other determinations. Significant deviations from unity
are associated with deficiencies in the corresponding terms of particular
functionals or with an incomplete optimization procedure.Comment: 5 pages, 2 figures, accepted for publication in Phys. Rev.
Empirical Abundance Scaling Laws and Implications for the Gamma-Process in Core-Collapse Supernovae
Analyzing the solar system abundances, we have found two empirical abundance
scaling laws concerning the p- and s-nuclei with the same atomic number. The
first scaling is s/p ratios are almost constant over a wide range of the atomic
number, where the p-nculei are lighter than the s-nuclei by two or four
neutrons. The second scaling is p/p ratios are almost constant, where the
second -nuclei are lighter than the first p-nucleus by two neutrons. These
scalings are a piece of evidence that most p-nuclei are dominantly synthesized
by the gamma-process in supernova explosions. The scalings lead to a novel
concept of "universality of gamma-process" that the s/p and p/p ratios of
nuclei produced by individual gamma-processes are almost constant,
respectively. We have calculated the ratios by gamma-process based on
core-collapse supernova explosion models under various astrophysical conditions
and found that the scalings hold for materials produced by individual
gamma-processes independent of the astrophysical conditions assumed. The
universality originates from three mechanisms: the shifts of the gamma-process
layers to keep their peak temperature, the weak s-process in pre-supernovae,
and the independence of the s/p ratios of the nuclear reactions. The results
further suggest an extended universality that the s/p ratios in the
gamma-process layers are not only constant but also centered on a specific
value of 3. With this specific value and the first scaling, we estimate that
the ratios of -process abundance contributions from the AGB stars to the
massive stars are almost 6.7 for the -nuclei of A > 90. We find that large
enhancements of s/p ratios for Ce, Er, and W are a piece of evidence that the
weak s-process actually occurred before SNe.Comment: 35 pages, 15 figure
P-Process Nucleosynthesis inside Supernova-Driven Supercritical Accretion Disks
We investigate p-process nucleosynthesis in a supercritical accretion disk
around a compact object of 1.4 M_solar, using the self-similar solution of an
optically thick advection dominated flow. Supercritical accretion is expected
to occur in a supernova with fallback material accreting onto a new-born
compact object. It is found that appreciable amounts of p-nuclei are
synthesized via the p-process in supernova-driven supercritical accretion disks
(SSADs) when the accretion rate m_dot = M_dot c^2/(16 L_Edd) >10^5, where L_Edd
is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs
have similar feature to those of the oxygen/neon layers in Type II supernovae
when the abundance of the fallback gas far from the compact object is that of
the oxygen/neon layers in the progenitor. The overall abundance profile is in
agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and
La, are underproduced in the SSADs as in Type II supernovae. If the fallback
gas is mixed with a small fraction of proton through Rayleigh-Taylor
instability during the explosion, significant amounts of Mo92 are produced
inside the SSADs. Ru96 and La138 are also produced when the fallback gas
contains abundant proton though the overall abundance profile of p-nuclei is
rather different from that of the solar system. The p-process nucleosynthesis
in SSADs contributes to chemical evolution of p-nuclei, in particular Mo92, if
several percents of fallback matter are ejected via jets and/or winds.Comment: 15 pages, 7 figures included, 3 tables, LaTeX emulateapj5.sty,
accepted for publication by the Astronomical Journal (March, 2003
Investigation of alpha-induced reactions on 130Ba and 132Ba and their importance for the synthesis of heavy p nuclei
Captures of alpha particles on the proton-richest Barium isotope, 130Ba, have
been studied in order to provide cross section data for the modeling of the
astrophysical gamma process. The cross sections of the 130Ba(alpha,gamma)134Ce
and 130Ba(alpha,n)133Ce reactions have been measured with the activation
technique in the center-of mass energy range between 11.6 and 16 MeV, close
above the astrophysically relevant energies. As a side result, the cross
section of the 132Ba(alpha,n)135Ce reaction has also been measured. The results
are compared with the prediction of statistical model calculations, using
different input parameters such as alpha+nucleus optical potentials. It is
found that the (alpha,n) data can be reproduced employing the standard
alpha+nucleus optical potential widely used in astrophysical applications.
Assuming its validity also in the astrophysically relevant energy window, we
present new stellar reaction rates for 130Ba(alpha,gamma)134Ce and
132Ba(alpha,gamma)136Ce and their inverse reactions calculated with the SMARAGD
statistical model code. The highly increased 136Ce(gamma,alpha)132Ba rate
implies that the p nucleus 130Ba cannot directly receive contributions from the
Ce isotopic chain. Further measurements are required to better constrain this
result.Comment: Accepted for publication in Phys. Rev.
Extended Skyrme interaction (I): spin fluctuations in dense matter
Most of the Skyrme interactions are known to predict spin or isospin
instabilities beyond the saturation density of nuclear matter which contradict
predictions based on realistic interactions. A modification of the standard
Skyrme interaction is proposed so that the ferromagnetic instability is
removed. The new terms are density dependent and modify only the spin p-h
interaction in the case of spin-saturated system. Consequences for the nuclear
response function and neutrino mean free path are shown. The overall effect of
the RPA correlations makes dense matter more transparent for neutrino
propagation by a factor of 2 to 10 depending of the density.Comment: 6 pages, 5 Figs., 2 Tab
Measurements of proton induced reaction cross sections on 120Te for the astrophysical p-process
The total cross sections for the 120Te(p,gamma)121I and 120Te(p,n)120I
reactions have been measured by the activation method in the effective
center-of-mass energies between 2.47 MeV and 7.93 MeV. The targets were
prepared by evaporation of 99.4 % isotopically enriched 120Te on Aluminum and
Carbon backing foils, and bombarded with proton beams provided by the FN tandem
accelerator at the University of Notre Dame. The cross sections and factors
were deduced from the observed gamma ray activity, which was detected off-line
by two Clover HPGe detectors mounted in close geometry. The results are
presented and compared with the predictions of statistical model calculations
using the codes NON-SMOKER and TALYS.Comment: 17 pages, 5 figures, 5 tables, regular articl
Cross-section measurement of the Ba 130 (p,Îł) La 131 reaction for Îł -process nucleosynthesis
Background: Deviations between experimental data of charged-particle-induced reactions and calculations within the statistical model are frequently found. An extended data base is needed to address the uncertainties regarding the nuclear-physics input parameters in order to understand the nucleosynthesis of the neutron-deficient p nuclei. Purpose: A measurement of total cross-section values of the Ba130(p,Îł)La131 reaction at low proton energies allows a stringent test of statistical model predictions with different proton+nucleus optical model potentials. Since no experimental data are available for proton-capture reactions in this mass region around A â130, this measurement can be an important input to test the global applicability of proton+nucleus optical model potentials. Method: The total reaction cross-section values were measured by means of the activation method. After the irradiation with protons, the reaction yield was determined by use of Îł-ray spectroscopy using two clover-type high-purity germanium detectors. In total, cross-section values for eight different proton energies could be determined in the energy range between 3.6 MeV â€Ep†5.0 MeV, thus, inside the astrophysically relevant energy region. Results: The measured cross-section values were compared to Hauser-Feshbach calculations using the statistical model codes TALYS and SMARAGD with different proton+nucleus optical model potentials. With the semimicroscopic JLM proton+nucleus optical model potential used in the SMARAGD code, the absolute cross-section values are reproduced well, but the energy dependence is too steep at the lowest energies. The best description is given by a TALYS calculation using the semimicroscopic Bauge proton+nucleus optical model potential using a constant renormalization factor. Conclusions: The statistical model calculation using the Bauge semimicroscopic proton+nucleus optical model potential deviates by a constant factor of 2.1 from the experimental data. Using this model, an experimentally supported stellar reaction rate for proton capture on the p nucleus Ba130 was calculated. At astrophysical temperatures, an increase in the stellar reaction rate of 68% compared to rates obtained from the widely used NON-SMOKER code is found. This measurement extends the scarce experimental data base for charged-particle-induced reactions, which can be helpful to derive a more globally applicable proton+nucleus optical model potential.Peer reviewedFinal Accepted Versio
Astrophysical S-factors for fusion reactions involving C, O, Ne and Mg isotopes
Using the Sao Paulo potential and the barrier penetration formalism we have
calculated the astrophysical factor S(E) for 946 fusion reactions involving
stable and neutron-rich isotopes of C, O, Ne, and Mg for center-of-mass
energies E varying from 2 MeV to 18-30 MeV (covering the range below and above
the Coulomb barrier). We have parameterized the energy dependence S(E) by an
accurate universal 9-parameter analytic expression and present tables of fit
parameters for all the reactions. We also discuss the reduced 3-parameter
version of our fit which is highly accurate at energies below the Coulomb
barrier, and outline the procedure for calculating the reaction rates. The
results can be easily converted to thermonuclear or pycnonuclear reaction rates
to simulate various nuclear burning phenomena, in particular, stellar burning
at high temperatures and nucleosynthesis in high density environments.Comment: 30 pages including 11 tables, 4 figures, ADNDT, accepte
Skyrme Interaction and Nuclear Matter Constraints
This paper presents a detailed assessment of the ability of the 240 Skyrme
interaction parameter sets in the literature to satisfy a series of criteria
derived from macroscopic properties of nuclear matter in the vicinity of
nuclear saturation density at zero temperature and their density dependence,
derived by the liquid drop model, experiments with giant resonances and
heavy-ion collisions. The objective is to identify those parameterizations
which best satisfy the current understanding of the physics of nuclear matter
over a wide range of applications. Out of the 240 models, only 16 are shown to
satisfy all these constraints. Additional, more microscopic, constraints on
density dependence of the neutron and proton effective mass beta-equilibrium
matter, Landau parameters of symmetric and pure neutron nuclear matter, and
observational data on high- and low-mass cold neutron stars further reduce this
number to 5, a very small group of recommended Skyrme parameterizations to be
used in future applications of the Skyrme interaction of nuclear matter related
observables. Full information on partial fulfillment of individual constraints
by all Skyrme models considered is given. The results are discussed in terms of
the physical interpretation of the Skyrme interaction and the validity of its
use in mean-field models. Future work on application of the Skyrme forces,
selected on the basis of variables of nuclear matter, in Hartree-Fock
calculation of properties of finite nuclei, is outlined.Comment: 86 pages, 14 figure
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