4,175 research outputs found

    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.

    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.

    Comment on "187Re(gamma,n) cross section close to and above the neutron threshold"

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    The work of M\"uller et al. [Phys. Rev. C 73, 025804 (2006); astro-ph/0512603] provides interesting experimental data on neutron emission by photodisintegration of 187Re. However, the comparison to theory and the discussed implications for the Re/Os clock require considerable amendment.Comment: 2 pages; accepted for publication in Phys. Rev.

    Nuclear Partition Functions at Temperatures Exceeding 10^10 K

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    Nuclear partition functions were calculated for a grid of temperatures from 1.2x10^10 K to 2.75x10^11 K (1<=kT<=24 MeV) within a Fermi-gas approach, including all nuclides from the proton-dripline to the neutron-dripline with proton number 9<=Z<=85. The calculation is based on a nuclear level density description published elsewhere, thus extending the previous tables of partition functions beyond 10^10 K. Additional high temperature corrections had to be applied.Comment: 12 pages with 2 figures, accepted by Ap. J. Suppl.; additional material can be downloaded from http://ftp.nucastro.org/astro/fits/partfuncs

    General properties of astrophysical reaction rates in explosive nucleosynthesis

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    “Published under licence in Journal of Physics: Conference Series by IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.”Fundamental differences in the prediction of reaction rates with intermediate and heavy target nuclei compared to the ones with light nuclei are discussed, with special emphasis on stellar modifications of the rates. Ground and excited state contributions to the stellar rates are quantified, deriving a linear weighting of excited state contributions despite of a Boltzmann population of the nuclear states. A Coulomb suppression effect of the excited state contributions is identified, acting against the usual Q-value rule in some reactions. The proper inclusion of experimental data in revised stellar rates is shown, containing revised uncertainties. An application to the s-process shows that the actual uncertainties in the neutron capture rates are larger than would be expected from the experimental errors alone. Sensitivities of reaction rates and cross sections are defined and their application in reaction studies is discussed. The conclusion provides a guide to experiment as well as theory on how to best improve the rates used in astrophysical simulations and how to assess their uncertainties.Peer reviewe

    Nuclear Reactions For Nucleosynthesis Beyond Fe

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    Many more nuclear transitions have to be known in the determination of stellar reactivities for trans-iron nucleosynthesis than for reactions of light nuclei. This requires different theoretical and experimental approaches. Some of the issues specific for trans-iron nucleosynthesis are discussed.Comment: 6 pages, 3 figures; invited talk at Int. Conf. on "Nuclear Structure and Dynamics III", June 14-19, 2015, Portoroz, Slovenia; to appear in AIP Conf. Pro

    Astrophysical Reaction Rates as a Challenge for Nuclear Reaction Theory

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    The relevant energy ranges for stellar nuclear reactions are introduced. Low-energy compound and direct reactions are discussed. Stellar modifications of the cross sections are presented. Implications for experiments are outlined.Comment: 8 pages, 2 figures; invited talk at OMEG10, March 2010. To appear in the OMEG10 proceedings published by AI
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