70 research outputs found
Astrophysical S-factor for O+O within the adiabatic molecular picture
The astrophysical S-factor for O + O is investigated within the
adiabatic molecular picture. It very well explains the available experimental
data. The collective radial mass causes a pronounced resonant structure in the
S-factor excitation function, providing a motivation for measuring the O
+ O fusion cross section at deep sub-barrier energies.Comment: 5 pages, 2 figures, SOTANCP2008 Conference, Strasbourg, France, May
13-16, 2008, To appear in IJMP
Characterizing the astrophysical S-factor for C+C with wave-packet dynamics
A quantitative study of the astrophysically important sub-barrier fusion of
C+C is presented. Low-energy collisions are described in the
body-fixed reference frame using wave-packet dynamics within a nuclear
molecular picture. A collective Hamiltonian drives the time propagation of the
wave-packet through the collective potential-energy landscape. The fusion
imaginary potential for specific dinuclear configurations is crucial for
understanding the appearance of resonances in the fusion cross section. The
theoretical sub-barrier fusion cross sections explain some observed resonant
structures in the astrophysical S-factor. These cross sections monotonically
decline towards stellar energies. The structures in the data that are not
explained are possibly due to cluster effects in the nuclear molecule, which
are to be included in the present approach.Comment: Submitted to Physical Review C; 7 figure
Nuclear structure of the exotic mass region along the rp process path
Isomeric states in the nuclei along the rapid proton capture process path are
studied by the projected shell model. Emphasis is given to two waiting point
nuclei 68Se and 72Kr that are characterized by shape coexistence. Energy
surface calculations indicate that the ground state of these nuclei corresponds
to an oblate-deformed minimum, while the lowest state at the prolate-deformed
minimum can be considered as a shape isomer. The impact of these isomer states
on isotopic abundance in x-ray bursts is studied in a multi-mass-zone x-ray
burst model by assuming an upper-lower limit approach.Comment: Proceedings of Nuclei in Cosmos VIII, to appear in Nucl. Phys.
An Approximation for the rp-Process
Hot (explosive) hydrogen burning or the Rapid Proton Capture Process
(rp-process) occurs in a number of astrophysical environments. Novae and X-ray
bursts are the most prominent ones, but accretion disks around black holes and
other sites are candidates as well. The expensive and often multidimensional
hydro calculations for such events require an accurate prediction of the
thermonuclear energy generation, while avoiding full nucleosynthesis network
calculations. In the present investigation we present an approximation scheme
applicable in a temperature range which covers the whole range of all presently
known astrophysical sites. It is based on the concept of slowly varying
hydrogen and helium abundances and assumes a kind of local steady flow by
requiring that all reactions entering and leaving a nucleus add up to a zero
flux. This scheme can adapt itself automatically and covers situations at low
temperatures, characterized by a steady flow of reactions, as well as high
temperature regimes where a -equilibrium is established.
In addition to a gain of a factor of 15 in computational speed over a full
network calculation, and an energy generation accurate to more than 15 %, this
scheme also allows to predict correctly individual isotopic abundances. Thus,
it delivers all features of a full network at a highly reduced cost and can
easily be implemented in hydro calculations.Comment: 18 pages, LaTeX using astrobib and aas2pp4, includes PostScript
figures; Astrophysical Journal, in press. PostScript source also available at
http://quasar.physik.unibas.ch/preps.htm
44Ti and 56Ni in core-collapse supernovae
We investigate the physical conditions where 44Ti and 56Ni are created in
core-collapse supernovae. In this preliminary work we use a series of
post-processing network calculations with parametrized expansion profiles that
are representative of the wide range of temperatures, densities and
electron-to-baryon ratios found in 3D supernova simulations. Critical flows
that affect the final yields of 44Ti and 56Ni are assessed.Comment: To appear in the Conference Proceedings for the "10th Symposium on
Nuclei in the Cosmos (NIC X)", July 27 - August 1 2008, Mackinack Island,
Michigan, US
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