Dynamical r-process studies within the neutrino-driven wind scenario and its sensitivity to the nuclear physics input

We use results from long-time core-collapse supernovae simulations to investigate the impact of the late time evolution of the ejecta and of the nuclear physics input on the calculated r-process abundances. Based on the latest hydrodynamical simulations, heavy r-process elements cannot be synthesized in the neutrino-driven winds that follow the supernova explosion. However, by artificially increasing the wind entropy, elements up to A=195 can be made. In this way one can reproduce the typical behavior of high-entropy ejecta where the r-process is expected to occur. We identify which nuclear physics input is more important depending on the dynamical evolution of the ejecta. When the evolution proceeds at high temperatures (hot r-process), an (n,g)-(g,n) equilibrium is reached. While at low temperature (cold r-process) there is a competition between neutron captures and beta decays. In the first phase of the r-process, while enough neutrons are available, the most relevant nuclear physics input are the nuclear masses for the hot r-process and the neutron capture and beta-decay rates for the cold r-process. At the end of this phase, the abundances follow a steady beta flow for the hot r-process and a steady flow of neutron captures and beta decays for the cold r-process. After neutrons are almost exhausted, matter decays to stability and our results show that in both cases neutron captures are key for determining the final abundances, the position of the r-process peaks, and the formation of the rare-earth peak. In all the cases studied, we find that the freeze out occurs in a timescale of several seconds.Comment: 20 pages, 12 figures, submitted to Phys. Rev. C (improved version

Halflife of 56Ni in cosmic rays

A measurement of the 56Ni cosmic ray abundance has been discussed as a possible tool to determine the acceleration time scale of relativistic particles in cosmic rays. This conjecture will depend on the halflife of totally ionized 56Ni which can only decay by higher-order forbidden transitions. We have calculated this halflife within large-scale shell model calculations and find t_{1/2} \approx 4 \times 10^4 years, only slightly larger than the currently available experimental lower limit, but too short for 56Ni to serve as a cosmic ray chronometer.Comment: 3 pages, 1 figur

Gamma-Ray Bursts Black hole accretion disks as a site for the vp-process

We study proton rich nucleosynthesis in windlike outflows from gamma-ray bursts accretion disks with the aim to determine if such outflows are a site of the vp-process. The efficacy of this vp-process depends on thermodynamic and hydrodynamic factors. We discuss the importance of the entropy of the material, the outflow rate, the initial ejection point and accretion rate of the disk. In some cases the vp-process pushes the nucleosynthesis out to A~100 and produces light p-nuclei. However, even when these nuclei are not produced, neutrino induced interactions can significantly alter the abundance pattern and cannot be neglected.Comment: 9 pages, 16 figures, accepted for publication in Phys. Rev.