9,659 research outputs found

    Astrophysical Rates for Explosive Nucleosynthesis: Stellar and Laboratory Rates for Exotic Nuclei

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    A selected overview of stellar effects and reaction mechanisms with relevance to the prediction of astrophysical reaction rates far off stability is provided.Comment: 4 pages, 2 figures (contining 2 subfigures each); Proceedings of 10th Intl. Conference on Nucleus-Nucleus Collisions, Beijing, China, August 2009; to appear in Nuclear Physics

    Reaction Rate Sensitivity of the gamma-Process Path

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    The location of the (gamma,p)/(gamma,n) and (gamma,alpha)/(gamma,n) line at gamma-process temperatures is discussed, using recently published reaction rates based on global Hauser-Feshbach calculations. The results can directly be compared to previously published, classic gamma-process discussions. The nuclei exhibiting the largest sensitivity to uncertainties in nuclear structure and reaction parameters are specified.Comment: 4 pages, contribution to Nuclei in the Cosmos VIII, to appear in Nucl. Phys.

    The Importance of Parity-Dependence of the Nuclear Level Density in the Prediction of Astrophysical Reaction Rates

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    A simple description for obtaining the parity distribution of nuclear levels in the pf + g9/2 shell as a function of excitation energy was recently derived. We implement this in a global nuclear level density model. In the framework of the statistical model, cross sections and astrophysical reaction rates are calculated in the Fe region and compared to rates obtained with the common assumption of an equal distribution of parities. We find considerable differences, especially for reactions involving particles in the exit channel.Comment: 4 pages, to appear in the proceedings of CGS11 (Prague), World Scientifi

    Differences between stellar and laboratory reaction cross sections

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    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

    Radiogenic p-isotopes from type Ia supernova, nuclear physics uncertainties, and galactic chemical evolution compared with values in primitive meteorites

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    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

    The Karlsruhe Astrophysical Database of Nucleosynthesis in Stars Project - Status and Prospects

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    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

    Relevant energy ranges for astrophysical reaction rates

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    Effective energy windows (Gamow windows) of astrophysical reaction rates for (p,gamma), (p,n), (p,alpha), (alpha,gamma), (alpha,n), (alpha,p), (n,gamma), (n,p), and (n,alpha) on targets with 10<=Z<=83 from proton- to neutron-dripline are calculated using theoretical cross sections. It is shown that widely used approximation formulas for the relevant energy ranges are not valid for a large number of reactions relevant to hydrostatic and explosive nucleosynthesis. The influence of the energy dependence of the averaged widths on the location of the Gamow windows is discussed and the results presented in tabular form (also at http://download.nucastro.org/astro/gamow/).Comment: 8 pages, 12 figures; ASCII table of results at http://download.nucastro.org/astro/gamow/ ; slightly revised text, to appear in Phys. Rev.
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