Superheavy Elements and the R-Process

Abstract

Detailed, microscopic-macroscopic fission-barrier calculations have been carried out along the r-process path. It has been found that the results are qualitatively similar to the semiempirical results of Schramm and Fowler in that the r-process yield of nuclei with A > 290 is strongly dependent on the surface symmetry correction to the surface energy of the nucleus. If this surface symmetry correction is represented by the nuclear parameter K, then it can be said that the r-process will not produce nuclei with A > 290 if K > 2.3, whereas finite yields of superheavy elements are possible for K <% 2.3. Detailed calculations following the decay of nuclei from the -process path back to the valley of beta stability (superheavy island) have been carried out. These calculations indicate that it is possible that the predicted longest-lived nucleus 294110 might not be produced in the r-process because fission competition during the decay back might deplete the (even-N, even-Z) nucleus. The details of the decay back were found to be extremely sensitive to the assumed rates, and thus no strong conclusions on abundance yields can be reached. This sensitivity is removed if N = 196 is a magic or semimagic number since there would be only negligible fission competition on the way from the r-process path to the island. The large number of assumptions and uncertainties going into superheavy elements and r-process calculations are discussed in detail. Subject headings: abundances, stellar - cosmic rays - nuclear reactions