765 research outputs found
Nucleation and cluster formation in low-density nucleonic matter: A mechanism for ternary fission
Ternary fission yields in the reaction 241Pu(nth,f) are calculated using a
new model which assumes a nucleation-time moderated chemical equilibrium in the
low density matter which constitutes the neck region of the scissioning system.
The temperature, density, proton fraction and fission time required to fit the
experimental data are derived and discussed. A reasonably good fit to the
experimental data is obtained. This model provides a natural explanation for
the observed yields of heavier isotopes relative to those of the lighter
isotopes, the observation of low proton yields relative to 2H and 3H yields and
the non-observation of 3He, all features which are shared by similar thermal
neutron induced and spontaneous fissioning systems.Comment: 6 pages, 3 figure
Symmetry energy of dilute warm nuclear matter
The symmetry energy of nuclear matter is a fundamental ingredient in the
investigation of exotic nuclei, heavy-ion collisions and astrophysical
phenomena. New data from heavy-ion collisions can be used to extract the free
symmetry energy and the internal symmetry energy at subsaturation densities and
temperatures below 10 MeV. Conventional theoretical calculations of the
symmetry energy based on mean-field approaches fail to give the correct
low-temperature, low-density limit that is governed by correlations, in
particular by the appearance of bound states. A recently developed quantum
statistical (QS) approach that takes the formation of clusters into account
predicts symmetry energies that are in very good agreement with the
experimental data. A consistent description of the symmetry energy is given
that joins the correct low-density limit with quasiparticle approaches valid
near the saturation density.Comment: 4 pages, 2 figures, 1 tabl
Novel technique to extract experimental symmetry free energy information of nuclear matter
A new method of accessing information on the symmetry free energy from yields
of fragments produced in Fermi-energy heavy-ion collisions is proposed.
Furthermore, by means of quantum fluctuation analysis techniques, correlations
between extracted symmetry free-energy coefficients with temperature and
density were studied. The obtained results are consistent with those of
commonly used isoscaling techniques.Comment: 6 pages, 3 figures Heavy-ion nuclear reactions at Fermi energies,
Nuclear equation of State, Fragmentatio
Density determinations in heavy ion collisions
The experimental determination of freeze-out temperatures and densities from
the yields of light elements emitted in heavy ion collisions is discussed.
Results from different experimental approaches are compared with those of model
calculations carried out with and without the inclusion of medium effects.
Medium effects become of relevance for baryon densities above fm. A quantum statistical (QS) model incorporating medium
effects is in good agreement with the experimentally derived results at higher
densities. A densitometer based on calculated chemical equilibrium constants is
proposed.Comment: 5 pages, 3 figure
Terahertz frequency standard based on three-photon coherent population trapping
A scheme for a THz frequency standard based on three-photon coherent
population trapping in stored ions is proposed. Assuming the propagation
directions of the three lasers obey the phase matching condition, we show that
stability of few 10 at one second can be reached with a precision
limited by power broadening to in the less favorable case. The
referenced THz signal can be propagated over long distances, the useful
information being carried by the relative frequency of the three optical
photons.Comment: article soumis a PRL le 21 mars 2007, accepte le 10 mai, version 2
(24/05/2007
Spin-zero anomaly in the magnetic quantum oscillations of a two-dimensional metal
We report on an anomalous behavior of the spin-splitting zeros in the de
Haas-van Alphen (dHvA) signal of a quasi-two-dimensional organic
superconductor. The zeros as well as the angular dependence of the amplitude of
the second harmonic deviate remarkably from the standard Lifshitz-Kosevich (LK)
prediction. In contrast, the angular dependence of the fundamental dHvA
amplitude as well as the spin-splitting zeros of the Shubnikov-de Haas signal
follow the LK theory. We can explain this behavior by small chemical-potential
oscillations and find a very good agreement between theory and experiment. A
detailed wave-shape analysis of the dHvA signal corroborates the existence of
an oscillating chemical potential
Active optics for the interrogation of a single ion
4 pagesInternational audienceThe signal-to-noise ratio in the detection of a single ion is one of the determining factors in the speed of the detection of the ion's internal states. Its value defines the necessary interrogation time to distinguish between an ion in the "on" and an ion in the "off" state. The improvement of the detection signal by means of active optics is a new approach in single-ion experiments. They accompany further progress in the stabilization of the clock laser for the single ion interrogation
Caloric curves and critical behavior in nuclei
Data from a number of different experimental measurements have been used to
construct caloric curves for five different regions of nuclear mass. These
curves are qualitatively similar and exhibit plateaus at the higher excitation
energies. The limiting temperatures represented by the plateaus decrease with
increasing nuclear mass and are in very good agreement with results of recent
calculations employing either a chiral symmetry model or the Gogny interaction.
This agreement strongly favors a soft equation of state. Evidence is presented
that critical excitation energies and critical temperatures for nuclei can be
determined over a large mass range when the mass variations inherent in many
caloric curve measurements are taken into account.Comment: In response to referees comments we have improved the discussion of
the figures and added a new figure showing the relationship between the
effective level density and the excitation energy. The discussion has been
reordered and comments are made on recent data which support the hypothesis
of a mass dependence of caloric curve
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