511 research outputs found
A Thomas-Fermi model of localization of proton impurities in neutron matter
We show that the proton impurity in a neutron matter can create an inhomogeneity in density which acts as a potential well localizing the proton’s wave function. At low densities this inhomogeneity is a neutron bulge, whereas at high densities a neutron deficiency (bubble) occurs. We calculate variationally the proton’s energy using a Gaussian wave function. The neutron background is treated in a Thomas–Fermi approximation. The Skyrme interactions are used. We find that the localized proton has lower energy than the plane wave proton for densities below the lower critical density n 0.3n, and above the upper critical density n 2.2n, where n = 0.17 fm. We discuss some implications of the proton localization for magnetic properties of neutron matter containing a small admixture of protons
Mixed quark-nucleon phase in neutron stars and nuclear symmetry energy
The influence of the nuclear symmetry energy on the formation of a mixed
quark-nucleon phase in neutron star cores is studied. We use simple
parametrizations of the nuclear matter equation of state, and the bag model for
the quark phase. The behavior of nucleon matter isobars, which is responsible
for the existence of the mixed phase, is investigated. The role of the nuclear
symmetry energy changes with the value of the bag constant B. For lower values
of B the properties of the mixed phase do not depend strongly on the symmetry
energy. For larger B we find that a critical pressure for the first quark
droplets to form is strongly dependent on the nuclear symmetry energy, but the
pressure at which last nucleons disappear is independent of it.Comment: 12 pages, 16 figures, Phys. Rev. C in pres
Shell model study of the pairing correlations
A systematic study of the pairing correlations as a function of temperature
and angular momentum has been performed in the sd-shell region using the
spherical shell model approach. The pairing correlations have been derived for
even-even, even-odd and odd-odd systems near N=Z and also for the asymmetric
case of N=Z+4. The results indicate that the pairing content and the behavior
of pair correlations is similar in even-even and odd-mass nuclei. For odd-odd
N=Z system, angular momentum I=0 state is an isospin, t=1 neutron-proton paired
configuration. Further, these t=1 correlations are shown to be dramatically
reduced for the asymmetric case of N=Z+4. The shell model results obtained are
qualitatively explained within a simplified degenerate model
Lifetime Measurements in 120Xe
Lifetimes for the lowest three transitions in the nucleus Xe have
been measured using the Recoil Distance Technique. Our data indicate that the
lifetime for the transition is more than a factor of
two lower than the previously adopted value and is in keeping with more recent
measurements performed on this nucleus. The theoretical implications of this
discrepancy and the possible reason for the erroneous earlier results are
discussed. All measured lifetimes in Xe, as well as the systematics of
the lifetimes of the 2 states in Xe isotopes, are compared with
predictions of various models. The available data are best described by the
Fermion Dynamic Symmetry Model (FDSM).Comment: 9 pages, RevTeX, 3 figures with Postscript file available on request
at [email protected], [email protected]. Submitted to Phys.
Rev.
Low Energy Skyrmion-Skyrmion Scattering
We study the scattering of Skyrmions at low energy and large separation using
the method proposed by Manton of truncation to a finite number of degrees
freedom. We calculate the induced metric on the manifold of the union of
gradient flow curves, which for large separation, to first non-trivial order is
parametrized by the variables of the product ansatz. (presented at the Lake
Louise Winter Institute, 1994)Comment: 6 page
Degeneracies when T=0 Two Body Matrix Elements are Set Equal to Zero and Regge's 6j Symmetry Relations
The effects of setting all T=0 two body interaction matrix elements equal to
a constant (or zero) in shell model calculations (designated as ) are
investigated. Despite the apparent severity of such a procedure, one gets
fairly reasonable spectra. We find that using in single j shell
calculations degeneracies appear e.g. the and
states in Sc are at the same excitation energies; likewise the
I=,,9 and 10 states in Ti. The
above degeneracies involve the vanishing of certain 6j and 9j symbols. The
symmetry relations of Regge are used to explain why these vanishings are not
accidental. Thus for these states the actual deviation from degeneracy are good
indicators of the effects of the T=0 matrix elements. A further indicator of
the effects of the T=0 interaction in an even - even nucleus is to compare the
energies of states with odd angular momentum with those that are even
Shifting the quantum Hall plateau level in a double layer electron system
We study the plateaux of the integer quantum Hall resistance in a bilayer
electron system in tilted magnetic fields. In a narrow range of tilt angles and
at certain magnetic fields, the plateau level deviates appreciably from the
quantized value with no dissipative transport emerging. A qualitative account
of the effect is given in terms of decoupling of the edge states corresponding
to different electron layers/Landau levels.Comment: 3 pages, 3 figures include
Settling the half-life of ⁶⁰Fe: fundamental for a versatile astrophysical chronometer
In order to resolve a recent discrepancy in the half-life of ⁶⁰Fe, we performed an independent measurement with a new method that determines the ⁶⁰Fe content of a material relative to Fe55 (t1/2=2.744yr) with accelerator mass spectrometry. Our result of (2.50±0.12)×10⁶yr clearly favors the recently reported value (2.62±0.04)×10⁶yr, and rules out the older result of (1.49±0.27)×10⁶yr. The present weighted mean half-life value of (2.60±0.05)×10⁶yr substantially improves the reliability as an important chronometer for astrophysical applications in the million-year time range. This includes its use as a sensitive probe for studying recent chemical evolution of our Galaxy, the formation of the early Solar System, nucleosynthesis processes in massive stars, and as an indicator of a recent nearby supernova.Part of this work was funded by the Austrian Science
Fund (FWF) Projects No. AP20434 and AI00428 (FWF
and CoDustMas, Eurogenesis via ESF)
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