Session 3WPA: The Origin of the Heavy Elements I

Transuranic Fission Fragments in Stars

Recent observations of the chemical compositions of metal-poor stars suggest that fission fragments of transuranic elements contributed to the abundance patterns of stars enhanced in products of rapid neutron-capture process (r-process) nucleosynthesis. The elements Ru, Rh, Pd, and Ag (atomic numbers 44 ≤ Z ≤ 47, mass numbers 99 ≤ A ≤ 110) and heavier elements (63 ≤ Z ≤ 78, A > 150) appear to be coproduced as the lighter and heavier fission fragment peaks from transuranic nuclei. If so, then nuclei with A > 260 may be regularly produced in r-process events. I will present the evidence for this discovery, and I will explore how this signature can be used to break the degeneracy between "yields" and "dilution" in star-forming environments, such as the low-mass dwarf galaxies where r-process-enhanced stars are likely born.   

Neutrino interactions and radioactive nuclear reactions in explosive nucleosynthesis of heavy nuclei

Heavy nuclei are produced by various nuclear processes such as r-, ν-, νp-, γ/p- and s-processes in massive stars as well as small-to-intermediate mass stars. Especially, the r-, ν- and νp-processes among them are strongly affected by the ν-nucleus interactions which leave observational signals to constrain still unknown neutrino mass hierarchy. Several light-mass nuclear reactions of radioactive unstable nuclei also play the important roles in the nucleosynthesis. In this talk we will first discuss our Galactic chemical evolution studies of heavy nuclei and show that the supernovae (both ν-driven winds and magneto-hydrodynamic jet SNe), the collapsars (the collapse and explosion of very massive stars leaving a black hole instead of neutron star as a remnant) and the binary neutron-star mergers are the viable astrophysical sites for explosive nucleosynthesis associated with ν-interactions in high density matter. We will secondly discuss the effects of neutrino-flavor oscillation due to collective oscillation and MSW effect and the roles of radioactive nuclear reactions on the nucleosynthesis. We will finally propose how to constrain the neutrino mass hierarchy in our nucleosynthetic method.