26,328 research outputs found
Overlap of quasiparticle random-phase approximation states for nuclear matrix elements of the neutrino-less double beta decay
Quasiparticle random-phase approximation (QRPA) is applied to two nuclei, and
overlap of the QRPA excited states based on the different nuclei is calculated.
The aim is to calculate the overlap of intermediate nuclear states of the
double-beta decay. We use the like-particle QRPA after the closure
approximation is applied to the nuclear matrix elements. The overlap is
calculated rigorously by making use of the explicit equation of the QRPA ground
state. The formulation of the overlap is shown, and a test calculation is
performed. The effectiveness of the truncations used is shown.Comment: 3 minor corrections and 1 minor chang
Emission FTIR analyses of thin microscopic patches of jet fuel residues deposited on heated metal surfaces
The relationship of fuel stability to fuel composition and the development of mechanisms for deposit formation were investigated. Fuel deposits reduce heat transfer efficiency and increase resistance to fuel flow and are highly detrimental to aircraft performance. Infrared emission Fourier transform spectroscopy was chosen as the primary method of analysis because it was sensitive enough to be used in-situ on tiny patches of monolayers or of only a few molecular layers of deposits which generally proved completely insoluble in any nondestructive solvents. Deposits of four base fuels were compared; dodecane, a dodecane/tetralin blend, commercial Jet A fuel, and a broadened-properties jet fuel particularly rich in polynuclear aromatics. Every fuel in turn was provided with and without small additions of such additives as thiophene, furan, pyrrole, and copper and iron naphthenates
Emission FTIR analyses of thin microscopic patches of jet fuel residue deposited on heated metal surface
Deposits laid down in patches on metal strips in a high pressure/high temperature fuel system simulator operated with aerated fuel at varying flow rates were analyzed by emission FTIR in terms of functional groups. Significant differences were found in the spectra and amounts of deposits derived from fuels to which small concentrations of oxygen-, nitrogen-, or sulfur-containing heterocyclics or metal naphthenates were added. The spectra of deposits generated on strips by heating fuels and air in a closed container were very different from those of the flowing fluid deposits. One such closed-container dodecane deposit on silver gave a strong surface-enhanced Raman spectrum
Limit on T-violating P-conserving rhoNN interaction from the gamma decay of Fe-57
We use the experimental limit on the interference of M1 and E2 multipoles in the γ decay of 57Fe to bound the time-reversal-violating parity-conserving ρNN vertex. Our approach is a large-basis shell-model calculation of the interference. We find an upper limit on the parameter g¯ρ, the relative strength of the T-violating ρNN vertex, of close to 10^(-2), a value similar to the best limits from other experiments
Quasielastic neutrino scattering from oxygen and the atmospheric neutrino problem
We examine several phenomena beyond the scope of Fermi-gas models that affect
the quasielastic scattering (from oxygen) of neutrinos in the 0.1 -- 3.0 GeV
range. These include Coulomb interactions of outgoing protons and leptons, a
realistic finite-volume mean field, and the residual nucleon-nucleon
interaction. None of these effects are accurately represented in the Monte
Carlo simulations used to predict event rates due to and neutrinos
from cosmic-ray collisions in the atmosphere. We nevertheless conclude that the
neglected physics cannot account for the anomalous to ratio observed
at Kamiokande and IMB, and is unlikely to change absolute event rates by more
than 10--15\%. We briefly mention other phenomena, still to be investigated in
detail, that may produce larger changes.Comment: In Revtex version 2. 14 pages, 3 figures (available on request from
J. Engel, tel. 302-831-4354, [email protected]
Probing r-Process Production of Nuclei Beyond Bi209 with Gamma Rays
We estimate gamma-ray fluxes due to the decay of nuclei beyond Bi209 from a
supernova or a supernova remnant assuming that the r-process occurs in
supernovae. We find that a detector with a sensitivity of about 10**(-7)
photons/cm**2/s at energies of 40 keV to 3 MeV may detect fluxes due to the
decay of Ra226, Th229, Am241, Am243, Cf249, and Cf251 in the newly discovered
supernova remnant near Vela. In addition, such a detector may detect fluxes due
to the decay of Ac227 and Ra228 produced in a future supernova at a distance of
about 1 kpc. As nuclei with mass numbers A > 209 are produced solely by the
r-process, such detections are the best proof for a supernova r-process site.
Further, they provide the most direct information on yields of progenitor
nuclei with A > 209 at r-process freeze-out. Finally, detection of fluxes due
to the decay of r-process nuclei over a range of masses from a supernova or a
supernova remnant provides the opportunity to compare yields in a single
supernova event with the solar r-process abundance pattern.Comment: 24 pages, 3 figures, to appear in the October 10, 1999 issue of Ap
Supernovae as the Site of the r-Process: Implications for Gamma-Ray Astronomy
We discuss how detection of gamma-ray emission from the decay of r-process
nuclei can improve our understanding of r-process nucleosynthesis. We find that
a gamma-ray detector with a sensitivity of 10**(-7)/cm**2/s at 100-700 keV may
detect the emission from the decay of Sb125, Cs137, Ce144, Eu155, and Os194
produced in a future Galactic supernova. In addition, such a detector may
detect the emission from the decay of Sn126 in the Vela supernova remnant and
the diffuse emission from the decay of Sn126 produced by past supernovae in our
Galaxy. The required detector sensitivity is similar to what is projected for
the proposed Advanced Telescope for High Energy Nuclear Astrophysics (ATHENA).
Both the detection of gamma-ray emission from the decay of several r-process
nuclei (e.g., Sb125 and Os194) produced in future Galactic supernovae and the
detection of emission from the decay of Sn126 in the Vela supernova remnant
would prove that supernovae are a site of the r-process. Furthermore, the
former detection would allow us to determine whether or not the r-process
nuclei are produced in relative proportions specified by the solar r-process
abundance pattern in supernova r-process events. Finally, detection of diffuse
emission from the decay of Sn126 in our Galaxy would eliminate neutron
star/neutron star mergers as the main source for the r-process nuclei near mass
number A=126.Comment: 14 pages, AASTeX, submitted to the Astrophysical Journa
- …