401 research outputs found
From multifragmentation to supernovae and neutron stars
The thermodynamics properties of globally neutral dense stellar matter are
analyzed both in terms of mean field instabilities and structures beyond the
mean field. The mean field response to finite wavelenght fluctuations is
calculated with the realistic Sly230a effective interaction. A Monte Carlo
simulation of a schematic lattice Hamiltonian shows the importance of
calculations beyond the mean field to calculate the phase diagram of stellar
matter. The analogies and differences respect to the thermodynamics of nuclear
matter and finite nuclei are stressed.Comment: To be published in Acta Phys. Hung.
Ising analogue to compact-star matter
By constructing an Ising analogue of compact-star matter at sub-saturation
density we explored the effect of Coulomb frustration on the nuclear liquid-gas
phase transition. Our conclusions is twofold. First, the range of temperatures
where inhomogeneous phases form expands with increasing Coulomb-field strength.
Second, within the approximation of uniform electron distribution, the limiting
point upon which the phase-coexistence region ends does not exhibit any
critical behaviour. Possible astrophysics consequences and thermodynamical
connections are discussed.Comment: 4 pages, 3 figure
Thermodynamics of compact-star matter within an ising approach
International Conference on Nucleus Nucleus Collisions 2006International audienceIn the formation and evolution of compact stars, nuclear matter explores high thermal excursions and is the site of intense neutrino emission. Neutrino transport as well as structural properties of this matter depend on the presence of inhomogeneous phases (named âpastaâ phases), which are the result of Coulomb frustration of the Liquid-Gas phase transition. We take into account charge fluctuations by employing a frustrated lattice-gas model to which we impose a neutrality constraint by the addition of an homogeneous background of charge, representing delocalised electrons. Within this schematic model we highlight a generaic feature of the phase-transition phenomenology: the temperature interval where pasta phases are formed is enhanced by Coulomb-frustration effects. This result is at variance with the behaviour of frustrated ferromagnetic systems as well as hot nuclei and mean-field approaches. Moreover, the region of phase coexistence is not found to end upon a critical point, indicating that no critical opalescence can occur in compact-star matter
Optical properties of highly n-doped germanium obtained by in situ doping and laser annealing
High n-type doping in germanium is essential for many electronic and optoelectronic applications especially for high performance Ohmic contacts, lasing and mid-infrared plasmonics. We report on the combination of in situ doping and excimer laser annealing to improve the activation of phosphorous in germanium. An activated n-doping concentration of 8.8ââĂââ1019 cmâ3 has been achieved starting from an incorporated phosphorous concentration of 1.1ââĂââ1020 cmâ3. Infrared reflectivity data fitted with a multi-layer Drude model indicate good uniformity over a 350ânm thick layer. Photoluminescence demonstrates clear bandgap narrowing and an increased ratio of direct to indirect bandgap emission confirming the high doping densities achieved
Production of new neutron-rich isotopes of heavy elements in fragmentation reactions of U projectiles at 1 A GeV
The production of heavy neutron-rich nuclei has been investigated using cold
fragmentation reactions of U projectiles at relativistic energies. The
experiment performed at the high-resolving-power magnetic spectrometer FRS at
GSI allowed to identify 45 new heavy neutron-rich nuclei: Pt,
Au, Hg, Tl, Pb, Bi,
Po, At, Rn and Fr. The production
cross sections of these nuclei were also determined and used to benchmark
reaction codes that predict the production of nuclei far from stability.Comment: 5 pages, 2 figure
High-resolution velocity measurements on fully identified light nuclides produced in 56Fe + hydrogen and 56Fe + titanium systems
New experimental results on the kinematics and the residue production are
obtained for the interactions of 56Fe projectiles with protons and (nat)Ti
target nuclei, respectively, at theincident energy of 1 A GeV. The
titanium-induced reaction serves as a reference case for multifragmentation.
Already in the proton-induced reaction, the characteristics of the isotopic
cross sections and the shapes of the velocity spectra of light residues
indicate that high thermal energy is deposited in the system during the
collision. In the 56Fe+p system the high excitation seems to favour the onset
of fast break-up decays dominated by very asymmetric partitions of the
disassembling system. This configuration leads to the simultaneous formation of
one or more light fragments together with one heavy residue.Comment: 24 pages, 21 figures, 1 table, this work forms part of the PhD thesis
of P.Napolitani, background information on http://www-w2k.gsi.de/kschmidt
Fluorine effect on As diffusion in Ge
The enhanced diffusion of donor atoms, via a vacancy (V)-mechanism, severely affects the realization of ultrahigh doped regions in miniaturized germanium (Ge) based devices. In this work, we report a study about the effect of fluorine (F) on the diffusion of arsenic (As) in Ge and give insights on the physical mechanisms involved. With these aims we employed experiments in Ge co-implanted with F and As and density functional theory calculations. We demonstrate that the implantation of F enriches the Ge matrix in V, causing an enhanced diffusion of As within the layer amorphized by F and As implantation and subsequently regrown by solid phase epitaxy. Next to the end-of-range damaged region F forms complexes with Ge interstitials, that act as sinks for V and induce an abrupt suppression of As diffusion. The interaction of Ge interstitials with fluorine interstitials is confirmed by theoretical calculations. Finally, we prove that a possible F-As chemical interaction does not play any significant role on dopant diffusion. These results can be applied to realize abrupt ultra-shallow n-type doped regions in future generation of Ge-based devices
Production of -particle condensate states in heavy-ion collisions
The fragmentation of quasi-projectiles from the nuclear reaction +
at 25 MeV/nucleon was used to produce excited states candidates to
-particle condensation. The experiment was performed at LNS-Catania
using the CHIMERA multidetector. Accepting the emission simultaneity and
equality among the -particle kinetic energies as experimental criteria
for deciding in favor of the condensate nature of an excited state, we analyze
the and states of C and the state of O. A
sub-class of events corresponding to the direct 3- decay of the Hoyle
state is isolated.Comment: contribution to the 2nd Workshop on "State of the Art in Nuclear
Cluster Physics" (SOTANCP2), Universite Libre de Bruxelles (Belgium), May
25-28, 2010, to be published in the International Journal of Modern Physics
Production of medium-mass neutron-rich nuclei in reactions induced by 136Xe projectiles at 1 A GeV on a beryllium target
Production cross sections of medium-mass neutron-rich nuclei obtained in the
fragmentation of 136Xe projectiles at 1 A GeV have been measured with the
FRagment Separator (FRS) at GSI. 125Pd was identified for the first time. The
measured cross sections are compared to 238U fission yields and model
calculations in order to determine the optimum reaction mechanism to extend the
limits of the chart of the nuclides around the r-process waiting point at N=82.Comment: 9 pages, 6 figure
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