1,834 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
Neutrino-nucleus reactions and their role for supernova dynamics and nucleosynthesis
The description of nuclear reactions induced by supernova neutrinos has
witnessed significant progress during the recent years. At the energies and
momentum transfers relevant for supernova neutrinos neutrino-nucleus cross
sections are dominated by allowed transitions, however, often with
non-negligible contributions from (first) forbidden transitions. For several
nuclei allowed Gamow-Teller strength distributions could be derived from
charge-exchange reactions and from inelastic electron scattering data.
Importantly the diagonalization shell model has been proven to accurately
describe these data and hence became the appropriate tool to calculate the
allowed contributions to neutrino-nucleus cross sections for supernova
neutrinos. Higher multipole contributions are usually calculated within the
framework of the Quasiparticle Random Phase Approximation, which describes the
total strength and the position of the giant resonances quite well.
This manuscript reviews the recent progress achieved in calculating
supernova-relevant neutrino-nucleus cross sections and discusses its
verification by data. Moreover, the review summarizes also the impact which
neutrino-nucleus reactions have on the dynamics of supernovae and on the
associated nucleosynthesis. These include the absorption of neutrinos by nuclei
(the inverse of nuclear electron capture which is the dominating
weak-interaction process during collapse), inelastic neutrino-nucleus
scattering and nuclear de-excitation by neutrino-pair emission. We also discuss
the role of neutrino-induced reactions for the recently discovered
process, for the r-process and for the neutrino process, for which
neutrino-nucleus reactions have the largest impact. Finally, we briefly review
neutrino-nucleus reactions important for the observation of supernova neutrinos
by earthbound detectors. (Abridged)Comment: 77 pages, 29 figures, 4 tables, submitted to Progress in Particle and
Nuclear Physic
Supernova neutrinos and nucleosynthesis
Observations of metal-poor stars indicate that at least two different
nucleosynthesis sites contribute to the production of r-process elements. One
site is responsible for the production of light r-process elements Z<~50 while
the other produces the heavy r-process elements. We have analyzed recent
observations of metal-poor stars selecting only stars that are enriched in
light r-process elements and poor in heavy r-process elements. We find a strong
correlation between the observed abundances of the N=50 elements (Sr, Y and Zr)
and Fe. It suggest that neutrino-driven winds from core-collapse supernova are
the main site for the production of these elements. We explore this possibility
by performing nucleosynthesis calculations based on long term Boltzmann
neutrino transport simulations. They are based on an Equation of State that
reproduces recent constrains on the nuclear symmetry energy. We predict that
the early ejecta is neutron-rich with Ye ~ 0.48, it becomes proton rich around
4 s and reaches Ye = 0.586 at 9 s when our simulation stops. The
nucleosynthesis in this model produces elements between Zn and Mo, including
92Mo. The elemental abundances are consistent with the observations of the
metal-poor star HD 12263. For the elements between Ge and Mo, we produce mainly
the neutron-deficient isotopes. This prediction can be confirmed by
observations of isotopic abundances in metal-poor stars. No elements heavier
than Mo (Z=42) and no heavy r-process elements are produced in our
calculations.Comment: 18 pages, 5 figures, submitted to J. Phys. G: Nucl. Part. Phys.
(Focus issue "Nucleosynthesis and the role of neutrinos", ed. Baha Balantekin
and Cristina Volpe
- …