Qucosa – Hemholtz-Zentrum Dresden-Rossendorf
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The 4 pi - fragment - spectrometer FOBOS
Get PDFThe 4 π - fragment - spectrometer FOBOS developed for heavy-ion research at beam energies of 10 - 100 AMeV has been commissioned for physical experiments at the Flerov Laboratory of Nuclear Reactions of the Joint Institute for Nuclear Research in Dubna. Based on the logarithmic detector principle, it is able to register charged fragments from Protons up to heavy residual nuclei in a large dynamical range. Position-sensitive avalanche counters, axial ionization chambers and CsI(TI) scintillation detectors are arranged in three concentric detector shells. An array of phoswich detectors is used as a more granular forward detector at narrow polar angles. The modular concept of FOBOS allows for different experimental application in the field of exclusive fragment spectroscopy at medium multiplicities. For illustration the fragment spectroscopy studies concerning the spontaneous fission process and the fragmentation of hot nuclei by means of the FOBOS set-up are considered
Polarization Observables in the Reaction NN -> NN O|
Get PDFWe study the reaction NN → NNΦ slightly above the threshold within an extended one-boson exchange model which also accounts for uud knock-out. It is shown that olarization observables, like the beam-target asymmetry, are sensible quantities for identifying a ss admixture in the nucleon wave function on the few per cent level
Freeze-Out Time in Ultrarelativistic Heavy Ion Collisions from Coulomb Effects in Transverse Pion Spectra
Get PDFThe influence of the nuclear Coulomb field on transverse spectra of λ + and λ- measured in Pb + Pb reactions at 158 A GeV has been investigated. Pion trajectories are calculated in the field of an expanding fireball. The observed enhancement of the λ-/λ+ ratio at small momenta depends on the temperature and transverse expansion velocity of the source, the rapidity distribution of the net positive charge, and mainly the time of the freeze-out
Estimates of Dilepton Spectra from Open Charm and Bottom Decays in Relativistic Heavy-Ion Collisions
Get PDFThe spectra of lepton pairs from correlated open charm and bottom decays in ultrarelativistic heavy-ion collisions are calculated. Our approach includes energy loss effects of the fast heavy quarks in deconfined matter which are determined by temperature and density of the expanding parton medium. We find a strong suppression of the initial transverse momentum spectrum of heavy quarks due to the energy lass at LHC conditions. Within the central rapidity covered by the ALICE detector system, the dominant contribution from bottom decays to the high invariant mass dielectron spectrum is predicted
The Chiral Quark-Loop Soliton in a Hot Gas of Constituent Quarks
Get PDFWe consider a chiral one-loop hedgehog soliton of the bosonized SU(2)f Nambu & Jona-Lasinio model which is embedded in a liot medium of constituent quarks. Energy and radius of the soliton are determined in self-consistent mean-field approximation. Quasi-classical corrections to the soliton energy are derived by means of the pushing and cranking approaches. The corresponding inertial parameters are evaluated. It is shown that the inertial mass is equivalent to the total internal energy of the soliton. Corrected nucleon and ∆ isobar masses are calculated in dependence on temperature and density of the medium. As a result of the internal structure of the soliton which is controlled by the self-consistent mean field, the scaling between constituent quark mass and soliton mass is noticeable disturbed
Kühlmittelvermischung in Druckwasserreaktoren; Vergleich von Kühlmittelströmung und -vermischung in einem skalierten Modell des DWR Konvoi mit den Vorgängen im Originalreaktor; Rechnungen mit dem CFD-Code CFX 4.1
Get PDFEs ergab sich die Notwendigkeit, die Vermischungseffekte mit einem 1:5 skalierten Modell nachzuvollziehen. In dieser Arbeit wurden Skalierungseffekte hervorgehoben und ein Vergleich der Strömungen im Originalreaktor und 1:5 Plexiglasmodell mit Hilfe eines numerischen Strömungsberechnungsprogrammes vollzogen. Dabei wurde das Modell und der Originalreaktor möglichtst originalgetreu abgebildet und mit den kalten Strängen zusammen modelliert.Die Vergleichsrechnungen belegen, daß es ausreichend ist, die Vermischungsvorgänge in einem mindestens 1:6.6 skalierten Modell eines DWR zu untersuchen. Die Parameter (Druck, Temperatur, Geschwindigkeit) erlauben den Aufbau als Plexiglasmodell, das eine optische Beobachtung der Vermischung ermöglicht. Das Forschungszentrum Rossendorf hat mit dem Aufbau eines 1:5 Modells 1997 begonnen
Elastic Proton-Deuteron Backward Scattering: Relativistic Effets and Polarization Observables
Get PDFThe elastic proton-deuteron backward reaction is analyzed within a covariant approach based on the Bethe-Salpeter equation with realistic meson-exchange interaction. Lorentz boost and other relativistic effects in the cross section and spin correlation observables, like tensor analyzing power and polarization transfer etc., are investigated in explicit form. Results of numerical calculations for a compbte set of polarization observables are presented
