arXiv subjects
Publications and source records attributed to M. Rayet.
Photon-induced reactions play a key role in the nucleosynthesis of heavy neutron-deficient nuclei, the so-called p-nuclei. In this paper we review the present status of experiments on photon-induced reactions at energies of astrophysical importance and their relevance to p-process modeling.
The calculations of the p-process in the O/Ne layers of Type II supernovae are quite successful in reproducung the solar system content of p-nuclides. They predict, however, a significant underproduction of the rare odd-odd nuclide 138La. A model for the explosion of a 25 Mo star with solar metallicity is used to suggest that electron neutrino captures on 138Ba may well be its most efficient production mechanism. The responsibility of an inadequate prediction of the 138La and 139La photodisintegration rates in the too low production of 138La is also examined quantitatively. A detailed discussion of the theoretical uncertainties in these rates suggest that the required rate changes are probably too high to be fully plausible. Their measurement would be most welcome. They would help disentangling the relative contributions of thermonuclear and neutrino processes to the 138La production.
A review is presented of the p-process in Type II supernovae, one of its goals being to enlighten the changes in views on this nucleosynthesis mechanism since the work of Jean and Jim on the subject in 1975. Specific discussions are also devoted to cases of particular interest, like the light Mo and Ru stable isotopes, the rare nuclide 138La or the radionuclide 146Sm. Some comments of diverse natures are also made on the r-process. These considerations do not aim at really providing an exhaustive review of the many nuclear physics and astrophysics intricacies of this process. In contrast, they are hoped to complement or to put in perspective other views that are often expressed in relation with this nucleosynthesis mechanism
Using the ETFSI (extended Thomas-Fermi plus Strutinsky integral) method, we have calculated the fission barriers of nearly 2000 exotic nuclei, including all the neutron-rich nuclei up to A=318 that are expected to be relevant to the r-process, and all the superheavy nuclei in the vicinity of N=184, with Z<=120. Our calculations were performed with the Skyrme force SkSC4, which was determined in the ETFSI-1 mass fit. For proton-deficient nuclei in the region of N=184 we find the barriers to be much higher than previously believed, which suggests that the r-process path might continue to mass numbers well beyond 300. For the superheavy nuclei we typically find barrier heights of 6-7 MeV.
The most detailed calculations of the p-process call for its development in the O/Ne layers of Type II supernovae. In spite of their overall success in reproducing the solar system content of p-nuclides, they suggest a significant underproduction of the light Mo and Ru isotopes. On grounds of a model for the explosion of a 25 solar mass star with solar metallicity, we demonstrate that this failure might just be related to the uncertainties left in the rate of the 22Ne(alpha,n)25Mg neutron producing reaction. The latter indeed has a direct impact on the distribution of the s-process seeds for the p-process.
The most detailed calculations of the p-process call for its development in the O/Ne layers of Type II supernovae. In spite of their overall success in reproducing the solar system content of p-nuclides, they suggest a significant underproduction of the light Mo and Ru isotopes. On grounds of a model for the explosion of a 25 solar mass star with solar metallicity, we demonstrate that this failure might just be related to the uncertainties left in the rate of the 22Ne(alpha,n)25Mg neutron producing reaction. The latter indeed have a direct impact on the distribution of the s-process seeds for the p-process.