Latest documents http://publikationen.stub.uni-frankfurt.de/index/index/ Fri, 30 Jun 2006 11:30:58 +0200 Fri, 30 Jun 2006 11:30:58 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2481 Collisions of very heavy ions at energies close to the Coulomb barrier are discussed as a unique tool to study the behavior of the electron-positron field in the presence of strong external electromagnetic fields. To calculate the excitation processes induced by the collision dynamics, a semiclassical model is employed and adapted to describe the field-theoretical many-particle system. An expansion in the adiabatic molecular basis is chosen. Energies and matrix elements are calculated using the monopole approximation. In a supercritical (Z1+Z2≳173) quasiatomic system the 1s level joins the antiparticle continuum and becomes a resonance, rendering the neutral vacuum state unstable. Several methods of treating the corresponding time-dependent problem are discussed. A projection-operator technique is introduced for a fully dynamical treatment of the resonance. Positron excitation rates in s1/2 and p1/2 states are obtained by numerical solution of the coupled-channel equations and are compared with results from first- plus second-order perturbation theory. Calculations are performed for subcritical and supercritical collisions of Pb-Pb, Pb-U, U-U, and U-Cf. Strong relativistic deformations of the wave functions and the growing contributions from inner-shell bound states lead to a very steep Z dependence of positron production. The results are compared with available data from experiments done at GSI. Correlations between electrons and positrons are briefly discussed. Joachim Reinhardt; Berndt Müller; Walter Greiner article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2481 Fri, 30 Jun 2006 11:30:58 +0200 http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2479 We calculate the spin polarization of 1sσ vacancies and emitted δ electrons induced by the strong magnetic field (|Bmax|∼1016G) in collisions of very heavy ions (Z1+Z2=178). The electron excitations are determined by the solution of coupled-channel equations within the quasimolecular basis states including the vector potential. The formulation is extended to the many-electron case. Spin polarizations of the order of 5-10% for impact energies below the Coulomb barrier are predicted. Gerhard Soff; Joachim Reinhardt; Walter Greiner article http://publikationen.stub.uni-frankfurt.de/frontdoor/index/index/docId/2479 Fri, 30 Jun 2006 11:16:27 +0200