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.

Astrophysical Reaction Rates as a Challenge for Nuclear Reaction Theory

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

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

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

Possible solution to the alpha-potential mystery in the gamma-process and the Nd/Sm ratio in meteorites

Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.The 146Sm/144Sm ratio in the early solar system has been constrained by Nd/Sm isotope ratios in meteoritic material. Predictions of 146Sm and 144Sm production in the gamma-process in massive stars are at odds with these constraints and this is partly due to deficiences in the prediction of the reaction rates involved. The production ratio depends almost exclusively on the (gamma,n)/(gamma,alpha) branching at 148Gd. A measurement of 144Sm(alpha,gamma)148Gd at low energy had discovered considerable discrepancies between cross section predictions and the data. Although this reaction cross section mainly depends on the optical alpha+nucleus potential, no global optical potential has yet been found which can consistently describe the results of this and similar alpha-induced reactions. The untypically large deviation in 144Sm(alpha,gamma) can be explained, however, by low-energy Coulomb excitation which is competing with compound nucleus formation at very low energies. Low-energy (alpha,gamma) and (alpha,n) data on other nuclei can also be consistently explained in this way. Since Coulomb excitation does not affect alpha-emission, the 148Gd(gamma,alpha) rate is much higher than previously assumed. This leads to very small 146Sm/144Sm stellar production ratios, in even more pronounced conflict with the meteorite data