659 research outputs found
The impact of global nuclear mass model uncertainties on -process abundance predictions
Rapid neutron capture or `-process' nucleosynthesis may be responsible for
half the production of heavy elements above iron on the periodic table. Masses
are one of the most important nuclear physics ingredients that go into
calculations of -process nucleosynthesis as they enter into the calculations
of reaction rates, decay rates, branching ratios and Q-values. We explore the
impact of uncertainties in three nuclear mass models on -process abundances
by performing global monte carlo simulations. We show that root-mean-square
(rms) errors of current mass models are large so that current -process
predictions are insufficient in predicting features found in solar residuals
and in -process enhanced metal poor stars. We conclude that the reduction of
global rms errors below keV will allow for more robust -process
predictions.Comment: 5 pages, 3 figures, invited talk at the 15th International Symposium
on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15), to appear in
EPJ Web of Conference
The sensitivity of r-process nucleosynthesis to the properties of neutron-rich nuclei
About half of the heavy elements in the Solar System were created by rapid
neutron capture, or r-process, nucleosynthesis. In the r-process, heavy
elements are built up via a sequence of neutron captures and beta decays in
which an intense neutron flux pushes material out towards the neutron drip
line. The nuclear network simulations used to test potential astrophysical
scenarios for the r-process therefore require nuclear physics data (masses,
beta decay lifetimes, neutron capture rates, fission probabilities) for
thousands of nuclei far from stability. Only a small fraction of this data has
been experimentally measured. Here we discuss recent sensitivity studies that
aim to determine the nuclei whose properties are most crucial for r-process
calculations.Comment: 8 pages, 4 figures, submitted to the Proceedings of the Fifth
International Conference on Fission and Properties of Neutron-Rich Nuclei
(ICFN5
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Spectroscopy of ultrathin epitaxial rutile TiO[sub 2](110) films grown on W(100)
Epitaxial ultrathin titanium dioxide films of 0.3 to similar to 7 nm thickness on a metal single crystal substrate have been investigated by high resolution vibrational and electron spectroscopies. The data complement previous morphological data provided by scanned probe microscopy and low energy electron diffraction to provide very complete characterization of this system. The thicker films display electronic structure consistent with a stoichiometric TiO2 phase. The thinner films appear nonstoichiometric due to band bending and charge transfer from the metal substrate, while work function measurements also show a marked thickness dependence. The vibrational spectroscopy shows three clear phonon bands at 368, 438, and 829 cm(-1) (at 273 K), which confirms a rutile structure. The phonon band intensity scales linearly with film thickness and shift slightly to lower frequencies with increasing temperature, in accord with results for single crystals. (c) 2007 American Institute of Physics
Sensitivity studies for r-process nucleosynthesis in three astrophysical scenarios
In rapid neutron capture, or r-process, nucleosynthesis, heavy elements are
built up via a sequence of neutron captures and beta decays that involves
thousands of nuclei far from stability. Though we understand the basics of how
the r-process proceeds, its astrophysical site is still not conclusively known.
The nuclear network simulations we use to test potential astrophysical
scenarios require nuclear physics data (masses, beta decay lifetimes, neutron
capture rates, fission probabilities) for all of the nuclei on the neutron-rich
side of the nuclear chart, from the valley of stability to the neutron drip
line. Here we discuss recent sensitivity studies that aim to determine which
individual pieces of nuclear data are the most crucial for r-process
calculations. We consider three types of astrophysical scenarios: a traditional
hot r-process, a cold r-process in which the temperature and density drop
rapidly, and a neutron star merger trajectory.Comment: 8 pages, 4 figures, submitted to the Proceedings of the International
Nuclear Physics Conference (INPC) 201
r-Process Nucleosynthesis in Hot Accretion Disk Flows from Black Hole - Neutron Star Mergers
We consider hot accretion disk outflows from black hole - neutron star
mergers in the context of the nucleosynthesis they produce. We begin with a
three dimensional numerical model of a black hole - neutron star merger and
calculate the neutrino and antineutrino fluxes emitted from the resulting
accretion disk. We then follow the element synthesis in material outflowing the
disk along parameterized trajectories. We find that at least a weak r-process
is produced, and in some cases a main r-process as well. The neutron-rich
conditions required for this production of r-process nuclei stem directly from
the interactions of the neutrinos emitted by the disk with the free neutrons
and protons in the outflow.Comment: 10 pages, 4 figures, one table and additional references adde
Nucleosynthesis in the Outflow from Gamma Ray Burst Accretion Disks
We examine the nucleosynthesis products that are produced in the outflow from
rapidly accreting disks. We find that the type of element synthesis varies
dramatically with the degree of neutrino trapping in the disk and therefore the
accretion rate of the disk. Disks with relatively high accretion rates such as
10 M_solar/s can produce very neutron rich nuclei that are found in the r
process. Disks with more moderate accretion rates can produce copious amounts
of Nickel as well as the light elements such as Lithium and Boron. Disks with
lower accretion rates such as 0.1 M_solar/s produce large amounts of Nickel as
well as some unusual nuclei such as Ti-49, Sc-45, Zn-64, and Mo-92. This wide
array of potential nucleosynthesis products is due to the varying influence of
electron neutrinos and antineutrinos emitted from the disk on the
neutron-to-proton ratio in the outflow. We use a parameterization for the
outflow and discuss our results in terms of entropy and outflow acceleration.Comment: 12 pages, 12 figures; submitted to Ap
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