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

Astrophysical relevance of γ\gamma transition energies

The relevant gamma energy range is explicitly identified where additional gamma$ strength has to be located for having an impact on astrophysically relevant reactions. It is shown that folding the energy dependences of the transmission coefficients and the level density leads to maximal contributions for gamma energies of 2<=E_gamma<=4 MeV unless quantum selection rules allow isolated states to contribute. Under this condition, electric dipole transitions dominate. These findings allow to more accurately judge the relevance of modifications of the \gamma strength for astrophysics.Comment: 5 pages, 11 figures, version accepted as a Rapid Communication in Phys. Rev.

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

Quantification of nuclear uncertainties in nucleosynthesis of elements beyond Iron

Thomas Rauscher, 'Quantification of nuclear uncertainties in nucleosynthesis of elements beyond Iron', in Proceedings of Science, Vol. 7 (7) July 2015. Paper presented at the XIII Nuclei in the Cosmos Conference, 7-11 July 2014, Debrecen, Hungary. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.Nucleosynthesis beyond Fe poses additional challenges not encountered when studying astrophysical processes involving light nuclei. Generally higher temperatures and nuclear level densities lead to stronger contributions of transitions on excited target states. This may prevent cross section measurements to determine stellar reaction rates and theory contributions remain important. Furthermore, measurements often are not feasible in the astrophysically relevant energy range. Sensitivity analysis allows not only to determine the contributing nuclear properties but also is a handy tool for experimentalists to interpret the impact of their data on predicted cross sections and rates. It can also speed up future input variation studies of nucleosynthesis by simplifying an intermediate step in the full calculation sequence. Large-scale predictions of sensitivities and ground-state contributions to the stellar rates are presented, allowing an estimate of how well rates can be directly constrained by experiment. The reactions 185W(n,γ) and 186W(γ,n) are discussed as application examples. Studies of uncertainties in abundances predicted in nucleosynthesis simulations rely on the knowledge of reaction rate errors. An improved treatment of uncertainty analysis is presented as well as a recipe for combining experimental data and theory to arrive at a new reaction rate and its uncertainty. As an example, it is applied to neutron capture rates for the s-process, leading to larger uncertainties than previously assumed

Environmental legislation and the impact of lobbying activities

The paper is concerned with effects of lobbying activities by political pressure groups that wish to affect environmental legislation. Two interest groups are considered, environmentalists on the one hand and a polluters' lobby on the other. These two groups can influence the environmental policy in two ways. First, they support those political parties that promise to implement their favoured kind of environmental regulation. This support has an impact on election probabilities and, therefore, on the environmental policy measures implemented by the new government. The second way of influencing political decisions is to exert pressure on an existing government. These two approaches are used in the paper to address the questions of how environmental quality is affected by lobbying activities and how large the resource waste due to lobbying is.

Monte Carlo variations as a tool to assess nuclear physics uncertainties in nucleosynthesis studies

© 2019 IOP Publishing Limited. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. https://creativecommons.org/licenses/by/3.0/The propagation of uncertainties in reaction cross sections and rates of neutron-, proton-, and α-induced reactions into the final isotopic abundances obtained in nucleosynthesis models is an important issue in studies of nucleosynthesis and Galactic Chemical Evolution. We developed a Monte Carlo method to allow large-scale postprocessing studies of the impact of nuclear uncertainties on nucleosynthesis. Temperature-dependent rate uncertainties combining realistic experimental and theoretical uncertainties are used. From detailed statistical analyses uncertainties in the final abundances are derived as probability density distributions. Furthermore, based on rate and abundance correlations an automated procedure identifies the most important reactions in complex flow patterns from superposition of many zones or tracers. The method already has been applied to a number of nucleosynthesis processes.Peer reviewe

Stellar neutron capture reactions at low and high temperature

© The Author(s) 2022. This article is licensed under a Creative Commons Attribution 4.0 International License, to view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.The determination of astrophysical reaction rates requires different approaches depending on the conditions in hydrostatic and explosive burning. The focus here is on astrophysical reaction rates for radiative neutron capture reactions. Relevant nucleosynthesis processes not only involve the s-process but also the i-, r- and γ-processes, which from the nuclear perspective mainly differ in the relative interaction energies of neutrons and nuclei, and in the nuclear level densities of the involved nuclei. Emphasis is put on the difference between reactions at low and high temperature. Possible complications in the prediction and measurement of these reaction rates are illustrated and the connection between theory and experiment is addressed.Peer reviewe

Two effects relevant for the study of astrophysical reaction rates: gamma transitions in capture reactions and Coulomb suppression of the stellar enhancement

Nucleosynthesis processes involve reactions on several thousand nuclei, both close to and far off stability. The preparation of reaction rates to be used in astrophysical investigations requires experimental and theoretical input. In this context, two interesting aspects are discussed: (i) the relevant gamma transition energies in astrophysical capture reactions, and (ii) the newly discovered Coulomb suppression of the stellar enhancement factor. The latter makes a number of reactions with negative Q value more favorable for experimental investigation than their inverse reactions, contrary to common belief.Comment: 5 pages, 5 figures, to appear in the proceedings of CGS 13 (Int. Conf. Capture Gamma Ray Spectroscopy and Related Topics

Astrophysical Reaction Rates From Statistical Model Calculations

Theoretical reaction rates in the temperature range 0.01*10^9<=T[K]<=10.*10^9 are calculated in the statistical model (Hauser-Feshbach formalism) for targets with 10<=Z<=83 (Ne to Bi) and for a mass range reaching the neutron and proton driplines. Reactions considered are (n,gamma), (n,p), (n,alpha), (p,gamma), (p,alpha),(alpha,gamma), and their inverse reactions. Reaction rates as a function of temperature for thermally populated targets are given by analytic seven parameter fits. To facilitate comparison with experimental rates, the stellar enhancement factors are also tabulated. Two complete sets of rates have been calculated, one of which includes a phenomenological treatment of shell quenching for neutron-rich nuclei. These extensive datasets are provided on-line as electronic files, while a selected subset from one calculation is given as printed tables. A summary of the theoretical inputs and advice on the use of the provided tabulations is included.Comment: 22 pages of text and 1 table; accepted by Atomic Data Nuclear Data Tables; a preprint is also available from http://quasar.physik.unibas.ch/~tommy/adndt.htm