4,823 research outputs found
Differences between stellar and laboratory reaction cross sections
Nuclear reactions proceed differently in stellar plasmas than in the
laboratory due to the thermal effects in the plasma. On one hand, a target
nucleus is bombarded by projectiles distributed in energy with a distribution
defined by the plasma temperature. The most relevant energies are low by
nuclear physics standards and thus require an improved description of
low-energy properties, such as optical potentials, required for the calculation
of reaction cross sections. Recent studies of low-energy cross sections suggest
the necessity of a modification of the proton optical potential. On the other
hand, target nuclei are in thermal equilibrium with the plasma and this
modifies their reaction cross sections. It is generally expected that this
modification is larger for endothermic reactions. We show that there are many
exceptions to this rule.Comment: 4 pages, Proceedings of Nuclear Physics in Astrophysics 4, Frascati,
Italy; to appear in J. Phys. Conf. Serie
The Karlsruhe Astrophysical Database of Nucleosynthesis in Stars Project - Status and Prospects
The KADoNiS (Karlsruhe Astrophysical Database of Nucleosynthesis in Stars) project is an astrophysical online database for cross sections relevant for nucleosynthesis in the s process and the γ process. The s-process database (http://www.kadonis.org) was started in 2005 and is presently facing its 4th update (KADoNiS v1.0). The γ-process database (KADoNiS-p, http://www.kadonis.org/pprocess) was recently revised and re-launched in March 2013. Both databases are compilations for experimental cross sections with relevance to heavy ion nucleosynthesis. For the s process recommended Maxwellian averaged cross sections for kT=5-100 keV are given for more than 360 isotopes between 1H and 210Bi. For the γ-process database all available experimental data from (p, γ), (p, n), (p, α), (α, γ), (α, n), and (α, p) reactions between 70Ge and 209Bi in or close to the respective Gamow window were collected and can be compared to theoretical predictions. The aim of both databases is a quick and user-friendly access to the available data in the astrophysically relevant energy regions. © 2014 Elsevier Inc.Peer reviewe
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
Motion of nanodroplets near chemical heterogeneities
We investigate the dynamics of nanoscale droplets in the vicinity of chemical
steps which separate parts of a substrate with different wettabilities. Due to
long-ranged dispersion forces, nanodroplets positioned on one side of the step
perceive the different character of the other side even at some distances from
the step, leading to a dynamic response. The direction of the ensuing motion of
such droplets does not only depend on the difference between the equilibrium
contact angles on these two parts but in particular on the difference between
the corresponding Hamaker constants. Therefore the motion is not necessarily
directed towards the more wettable side and can also be different from that of
droplets which span the step.Comment: 6 pages, 6 figure
A thin film model for corotational Jeffreys fluids under strong slip
We derive a thin film model for viscoelastic liquids under strong slip which
obey the stress tensor dynamics of corotational Jeffreys fluids.Comment: 3 pages, submitted to Eur. Phys. J.
Coulomb suppression of the stellar enhancement factor
It is commonly assumed that reaction measurements for astrophysics should be
preferably performed in the direction of positive Q value to minimize the
impact of the stellar enhancement factor, i.e. the difference between the
laboratory rate and the actual stellar rate. We show that the stellar effects
can be minimized in the charged particle channel, even when the reaction Q
value is negative. As a demonstration, the cross section of the astrophysically
relevant 85Rb(p,n)85Sr reaction has been measured by activation between 2.16 <
Ec.m. < 3.96 MeV and the astrophysical reaction rate for (p,n) as well as (n,p)
is directly inferred from the data. The presented arguments are also relevant
for other alpha and proton-induced reactions in the p and rp processes.
Additionally, our results confirm a previously derived modification of a global
optical proton potential.Comment: submitted to PR
Measurement of (α,n) reaction cross sections of erbium isotopes for testing astrophysical rate predictions
Date of Acceptance: 30/01/2015The γ-process in core-collapse and/or type Ia supernova explosions is thought to explain the origin of the majority of the so-called p nuclei (the 35 proton-rich isotopes between Se and Hg). Reaction rates for γ-process reaction network studies have to be predicted using Hauser-Feshbach statistical model calculations. Recent investigations have shown problems in the prediction of α-widths at astrophysical energies which are an essential input for the statistical model. It has an impact on the reliability of abundance predictions in the upper mass range of the p nuclei. With the measurement of the 164,166Er(α,n)167,169Yb reaction cross sections at energies close to the astrophysically relevant energy range we tested the recently suggested low energy modification of the α+nucleus optical potential in a mass region where γ-process calculations exhibit an underproduction of the p nuclei. Using the same optical potential for the α-width which was derived from combined 162Er(α,n) and 162Er(α,γ) measurement makes it plausible that a low-energy modification of the optical α+nucleus potential is needed.Peer reviewedFinal Accepted Versio
Probing the Production of Actinides under Different r-process Conditions
Several extremely metal-poor stars are known to have an enhanced thorium abundance. These actinide-boost stars have likely inherited material from an r-process that operated under different conditions than the r-process that is reflected in most other metal-poor stars with no actinide enhancement. In this article, we explore the sensitivity of actinide production in r-process calculations to the hydrodynamical conditions as well as the nuclear physics. We find that the initial electron fraction Y e is the most important factor determining the actinide yields and that the abundance ratios between long-lived actinides and lanthanides like europium can vary for different conditions in our calculations. In our setup, conditions with high entropies systematically lead to lower actinide abundances relative to other r-process elements. Furthermore, actinide-enhanced ejecta can also be distinguished from the "regular" composition in other ways, most notably in the second r-process peak abundances.Peer reviewe
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