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- Viscous fluid dynamical calculation of the reaction 12C(85 MeV/nucleon) + 197Au (1983)
- Proton spectra have been calculated for the reaction 12C(85 MeV/nucleon) + 197Au using a three-dimensional hydrodynamical model with viscosity and thermal conductivity and final thermal breakup. The theoretical results are compared to recent data. It is shown that the predicted flow effects are not observable as a result of the impact parameter averaging inherent in the inclusive proton spectra. In contrast, angular distributions of medium mass nuclei (A>3) in nearly central collisions can provide signatures for flow effects.

- Viscosity and the equation of state in high energy heavy-ion reactions (1993)
- Viscous hydrodynamic calculations of high energy heavy-ion collisions (Nb-Nb and Au-Au) from 200 to 800 MeV/nucleon are presented. The resulting baryon rapidity distributions, the in-plane transverse momentum transfer (bounce-off), and the azimuthal dependence of the midrapidity particles (off-plane squeeze out) compare well with Plastic Ball data. We find that the considered observables are sensitive both to the nuclear equation of state and to the nuclear shear viscosity η. Transverse momentum distributions indicate a high shear viscosity (η≊60 MeV/fm2 c) in the compression zone, in agreement with nuclear matter estimates. The bulk viscosity ζ influences only the entropy production during the expansion stage; collective observables like flow and dN/dY do not depend strongly on ζ. The recently observed off-plane (φ=90°) squeeze-out, which is found in the triple-differential rapidity distribution, exhibits the strongest sensitivity to the nuclear equation of state. It is demonstrated that for very central collisions, b=1 fm, the squeeze-out is visible even in the double-differential cross section. This is experimentally accessible by studying azimuthally symmetric events, as confirmed recently by data of the European 4π detector collaboration at Gesellchaft für Schwerionforschung Darmstadt.

- Variable masses in fission and heavy-ion collisions (1972)
- With the use of the cranking formula, the coordinate-dependent mass parameters of the kinetic-energy operator in fission processes and heavy-ion collisions are calculated in the two-center oscillator model. It is shown that the reduced mass and also the classical moment of inertia are obtained for large separations of the fragments. For small separations, however, the mass parameter for the motion of the centers of mass of the fragments is larger than the reduced mass by an order of magnitude.

- Time-dependent Hartree-Fock studies of superheavy molecules (1983)
- The time dependent Hartree-Fock approximation is used to study the dynamical formation of long-lived superheavy nuclear complexes. The effects of long-range Coulomb polarization are treated in terms of a classical quadrupole polarization model. Our calculations show the existence of "resonantlike" structures over a narrow range of bombarding energies near the Coulomb barrier. Calculations of 238U + 238U are presented and the consequences of these results for supercritical positron emission are discussed. NUCLEAR REACTIONS 238U + 238U collisions as a function of bombarding energy, in the time-dependent Hartree-Fock approximation. Superheavy molecules and strongly damped collisions.

- Three-component fluid dynamics for the description of energetic heavy-ion reactions (1982)
- The nucleons taking part in heavy ion reaction are considered as a three-component fluid. The first and second components correspond to the nucleons of the target and the projectile, while the thermalized nucleons produced in the course of the collision belong to the third component. Making use of the Boltzmann equation, hydrodynamical equations are derived. An equation of state for anisotropic nuclear matter obtained from a field theoretical model in mean field approximation is applied in a one dimensional version of the three-component fluid model. The speed of thermalization is analyzed and compared to the results of cascade and kinetic models. NUCLEAR REACTIONS Relativistic heavy-ion reactions, hydrodynamic description.

- Thermal photons as a measure for the rapidity dependence of the temperature (1995)
- The rapidity distribution of thermal photons produced in Pb+Pb collisions at CERN-SPS energies is calculated within scaling and three- fluid hydrodynamics. It is shown that these scenarios lead to very different rapidity spectra. A measurement of the rapidity dependence of photon radiation can give cleaner insight into the reaction dynamics than pion spectra, especially into the rapidity dependence of the temperature.

- Theory of fission-mass distributions demonstrated for 226Ra, 236U, 258Fm (1973)
- With the mass asymmetry described by the dynamical collective fragmentation coordinate ξ, and with use of the asymmetric two-center shell model, the fission mass distributions for 226Ra, 236U, and 258Fm (which are typical representatives for triple-, double-, and single-humped distributions) are explained.

- The Phase Transition to the Quark-Gluon Plasma and Its Effect on Hydrodynamic Flow (1995)
- It is shown that in ideal relativistic hydrodynamics a phase transition from hadron to quark and gluon degrees of freedom in the nuclear matter equation of state leads to a minimum in the excitation function of the transverse collective flow.

- Shell structure of superheavy nuclei in self-consistent mean-field models (1999)
- We study the extrapolation of nuclear shell structure to the region of superheavy nuclei in self-consistent mean-field models—the Skyrme-Hartree-Fock approach and the relativistic mean-field model—using a large number of parametrizations which give similar results for stable nuclei but differ in detail. Results obtained with the folded-Yukawa potential which is widely used in macroscopic-macroscopic models are shown for comparison. We focus on differences in the isospin dependence of the spin-orbit interaction and the effective mass between the models and their influence on single-particle spectra. The predictive power of the mean-field models concerning single-particle spectra is discussed for the examples of 208Pb and the spin-orbit splittings of selected neutron and proton levels in 16O, 132Sn, and 208Pb. While all relativistic models give a reasonable description of spin-orbit splittings, all Skyrme interactions show a wrong trend with mass number. The spin-orbit splitting of heavy nuclei might be overestimated by 40%–80%, which exposes a fundamental deficiency of the current nonrelativistic models. In most cases the occurrence of spherical shell closures is found to be nucleon-number dependent. Spherical doubly magic superheavy nuclei are found at 184298114, 172292120, or 184310126 depending on the parametrization. The Z=114 proton shell closure, which is related to a large spin-orbit splitting of proton 2f states, is predicted only by forces which by far overestimate the proton spin-orbit splitting in 208Pb. The Z=120 and N=172 shell closures predicted by the relativistic models and some Skyrme interactions are found to be related to a central depression of the nuclear density distribution. This effect cannot appear in macroscopic-microscopic models or semiclassical approaches like the extended Thomas-Fermi-Strutinski integral approach which have a limited freedom for the density distribution only. In summary, our findings give a strong argument for 172292120 to be the next spherical doubly magic superheavy nucleus.

- Probes for the early reaction dynamics of heavy ion collisions at AGS and SPS (1997)
- We discuss the early evolution of ultrarelativistic heavy-ion collisions within a multi- fluid dynamical model. In particular, we show that due to the finite mean-free path of the particles compression shock waves are smeared out considerably as compared to the one-fluid limit. Also, the maximal energy density of the baryons is much lower. We discuss the time scale of kinetic equilibration of the baryons in the central region and its relevance for directed flow. Finally, thermal emission of direct photons from the fluid of produced particles is calculated within the three-fluid model and two other simple expansion models. It is shown that the transverse momentum and rapidity spectra of photons give clue to the cooling law and the early rapidity distribution of the photon source.