4,180 research outputs found
Reaction Rate Sensitivity of the gamma-Process Path
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
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"
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
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
“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
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
Photonuclear Reactions in Astrophysics
This is an Accepted Manuscript of an article published by Taylor & Francis Group in the journal Nuclear Physics News. Published on 12 Sep 2018, available online: https://doi.org/10.1080/10619127.2018.1463016Nucleosynthesis in stars and stellar explosions proceeds via nuclear reactions in thermalized plasmas. Nuclear reactions not only transmutate elements and their isotopes, and thus create all known elements from primordial hydrogen and helium, they also release energy to keep stars in hydrostatic equilibrium over astronomical timescales. A stellar plasma has to be hot enough to provide sufficient kinetic energy to the plasma components to overcome Coulomb barriers and to allow interactions between them. Plasma components in thermal equilibrium are bare atomic nuclei, free electrons, and photons (radiation). Typical temperatures of plasmas experiencing nuclear burning range from 107 K for hydrostatic hydrogen burning (mainly interactions among protons and He isotopes) to 1010 K or more in explosive events, such as supernovae or neutron star mergers. This still translates into low interaction energies by nuclear physics standards, as the most probable energy E between reaction partners in terms of temperature is derived from Maxwell-Boltzmann statistics and yields E = T9/11.6045 MeV, where T9 is the plasma temperature in GK.Peer reviewe
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