261 research outputs found
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.
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