4,040 research outputs found
Tables of Nuclear Cross Sections and Reaction Rates: an Addendum to the Paper "Astrophysical Reaction Rates from Statistical Model Calculations"
In a previous publication [Atomic Data and Nuclear Data Tables 75, 1 (2000)],
we had given seven parameter analytical fits to theoretical reaction rates
derived from nuclear cross sections calculated in the statistical model
(Hauser-Feshbach formalism) for targets with 9<Z<84 (Ne to Bi) and for a mass
range reaching the neutron and proton driplines. Reactions considered were
(n,gamma), (n,p), (n,alpha), (p,gamma), (p,alpha), (alpha,gamma), and their
inverse reactions. On public demand, we present here the theoretical nuclear
cross sections and astrophysical reaction rates from which those rate fits were
derived, and we provide these data as on-line electronic files. Corresponding
to the fitted rates, two complete data sets are provided, one of which includes
a phenomenological treatment of shell quenching for neutron-rich nuclei.Comment: 23 pages, 3 tables; scheduled to appear in Atomic Data Nuclear Data
Tables 79 (2001) (September issue); preprint and data also available at
http://quasar.physik.unibas.ch/~tommy/adndt.htm
Global statistical model calculations and the role of isospin
An improved code for the calculation of astrophysical reaction rates in the
statistical model is presented. It includes the possibility to study isospin
effects. Such effects heavily affect capture rates involving self-conjugate
nuclei and may also be found in reactions on other intermediate and heavy
targets.Comment: 5 pages LaTeX, uses iopconf.sty, to appear in the proceedings of the
2nd Oak Ridge Symposium on Atomic and Nuclear Astrophysics, ed. A.
Mezzacappa, IOP, in pres
Radiogenic p-isotopes from type Ia supernova, nuclear physics uncertainties, and galactic chemical evolution compared with values in primitive meteorites
The nucleosynthesis of proton-rich isotopes is calculated for multi-dimensional Chandrasekhar-mass models of Type Ia supernovae (SNe Ia) with different metallicities. The predicted abundances of the short-lived radioactive isotopes 92Nb, 97, 98Tc, and 146Sm are given in this framework. The abundance seeds are obtained by calculating s-process nucleosynthesis in the material accreted onto a carbon-oxygen white dwarf from a binary companion. A fine grid of s-seeds at different metallicities and 13C-pocket efficiencies is considered. A galactic chemical evolution model is used to predict the contribution of SN Ia to the solar system p-nuclei composition measured in meteorites. Nuclear physics uncertainties are critical to determine the role of SNe Ia in the production of 92Nb and 146Sm. We find that, if standard Chandrasekhar-mass SNe Ia are at least 50% of all SN Ia, they are strong candidates for reproducing the radiogenic p-process signature observed in meteorites.Peer reviewedFinal Accepted Versio
Comment on "Heavy element production in inhomogeneous big bang nucleosynthesis"
The work of Matsuura et al. [Phys. Rev. D 72, 123505 (2005);
astro-ph/0507439] claims that heavy nuclei could have been produced in a
combined p- and r-process in very high baryon density regions of an
inhomogeneous big bang. However, they do not account for observational
constraints and previous studies which show that such high baryon density
regions did not significantly contribute to big bang abundances.Comment: 2 pages, submitted to Phys. Rev. D on Feb 23, 200
Reaction Rates and Nuclear Properties Relevant for Nucleosynthesis in Massive Stars and Far From Stability
Explosive nuclear burning in astrophysical environments produces unstable
nuclei which again can be targets for subsequent reactions. In addition, it
involves a large number of stable nuclides which are not fully explored by
experiments, yet. Thus, it is necessary to be able to predict reaction cross
sections and thermonuclear rates with the aid of theoretical models. Such
predictions are also of interest for investigations at radioactive ion beam
facilities. An extended library of theoretical cross sections and reaction
rates is presented. The problem of alpha+nucleus potentials is addressed and
new parametrizations presented. The problem of properly predicting cross
sections at low level densities is illustrated by the 62Ni(n,gamma) reaction.Comment: 7 pages, invited talk, to appear in proceedings of CGS11 (Prague),
World Scientific (new version: fixed typo in potential parameters; note: they
will still be incorrect in the printed version
The 106Cd(α, α)106Cd elastic scattering in a wide energy range for γ process studies
Date of Acceptance: 15/04/2015Alpha elastic scattering angular distributions of the 106Cd(α, α)106Cd reaction were measured at three energies around the Coulomb barrier to provide a sensitive test for the α + nucleus optical potential parameter sets. Furthermore, the new high precision angular distributions, together with the data available from the literature were used to study the energy dependence of the locally optimized α + nucleus optical potential in a wide energy region ranging from ELab=27.0MeV down to 16.1 MeV.The potentials under study are a basic prerequisite for the prediction of α-induced reaction cross sections and thus, for the calculation of stellar reaction rates used for the astrophysical γ process. Therefore, statistical model predictions using as input the optical potentials discussed in the present work are compared to the available 106Cd + alpha cross section data.Peer reviewe
Parity-Dependence in the Nuclear Level Density
Astrophysical reaction rates are sensitive to the parity distribution at low
excitation energies. We combine a formula for the energy-dependent parity
distribution with a microscopic-macroscopic nuclear level density. This
approach describes well the transition from low excitation energies, where a
single parity dominates, to high excitations where the two densities are equal.Comment: 4 pages, 3 figures; contribution to Nuclei In The Cosmos VIII, to
appear in Nucl. Phys.
Testing the role of SNe Ia for galactic chemical evolution of p-nuclei with two-dimensional models and with s-process seeds at different metallicities
Date of Acceptance: 07/11/2014The bulk of p isotopes is created in the "gamma processes" mainly by sequences of photodisintegrations and beta decays in explosive conditions in Type Ia supernovae (SNIa) or in core collapse supernovae (ccSN). The contribution of different stellar sources to the observed distribution of p-nuclei in the solar system is still under debate. We explore single degenerate Type Ia supernovae in the framework of two-dimensional SNIa delayed-detonation explosion models. Travaglio et al. discussed the sensitivity of p-nuclei production to different SNIa models, i.e., delayed detonations of different strength, deflagrations, and the dependence on selected s-process seed distributions. Here we present a detailed study of p-process nucleosynthesis occurring in SNIa with s-process seeds at different metallicities. Based on the delayed-detonation model DDT-a of TRV11, we analyze the dependence of p-nucleosynthesis on the s-seed distribution obtained from different strengths of the 13C pocket. We also demonstrate that 208Pb seed alone changes the p-nuclei production considerably. The heavy-s seeds (140 ≤A < 208) contribute with about 30%-40% to the total light-p nuclei production up to 132Ba (with the exception of 94Mo and 130Ba, to which the heavy-s seeds contribute with about 15% only). Using a Galactic chemical evolution code from Travaglio et al., we study the contribution of SNIa to the solar stable p-nuclei. We find that explosions of Chandrasekhar-mass single degenerate systems produce a large amount of p-nuclei in our Galaxy, both in the range of light (A ≤ 120) and heavy p-nuclei, at almost flat average production factors (within a factor of about three). We discussed in details p-isotopes such as 94Mo with a behavior diverging from the average, which we attribute to uncertainties in the nuclear data or in SNIa modeling. Li et al. find that about 70% of all SNeIa are normal events. If these are explained in the framework of explosions of Chandrasekhar-mass white dwarfs resulting from the single-degenerate progenitor channel, we find that they are responsible for at least 50% of the p-nuclei abundances in the solar system.Peer reviewedFinal Accepted Versio
Thermal noise influences fluid flow in thin films during spinodal dewetting
Experiments on dewetting thin polymer films confirm the theoretical
prediction that thermal noise can strongly influence characteristic time-scales
of fluid flow and cause coarsening of typical length scales. Comparing the
experiments with deterministic simulations, we show that the Navier-Stokes
equation has to be extended by a conserved bulk noise term to accomplish the
observed spectrum of capillary waves. Due to thermal fluctuations the spectrum
changes from an exponential to a power law decay for large wavevectors. Also
the time evolution of the typical wavevector of unstable perturbations exhibits
noise induced coarsening that is absent in deterministic hydrodynamic flow.Comment: 4 pages, 3 figure
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