Atoms in extreme virtual photon fields of fast, highly charged ions

Highly-charged ions at velocities close to the speed of light generate strong (I = 10"1"7 - 10"2"0 W/cm"2), ultra-short (t = 10"-"1"9 - 10"-"1"7 s) electromagnetic pulses when passing target atoms or molecules. Single and multiple ionization occurs and can be interpreted in terms of photoionization: at small field strength ionization is due to the absorption or the scattering of a single virtual photon whereas the incoherent, ''simultaneous'' absorption of ''many'' field quanta gives rise to multiple ionization in strong fields. In this paper analogies to photoionization are investigated by comparison of kinematically complete experimental data with results of various theoretical calculations for collisions of 100 MeV/u C"6"+, 1000 MeV/u U"9"2"+ and 3.6 MeV/u Au"5"3"+ on He, Ne and Ar targets. Dynamical multiple ionization mechanisms are identified as a function of the momentum transfer. Two-electron final states are found to sensitively depend on the correlated initial state, and the many-particle Coulomb continuum is investigated for triple ionization of neon in super-strong fields. (orig.)29 refs.SIGLEAvailable from TIB Hannover: RO 801(99-29) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Double ionisation of helium in fast ion collisions: the role of momentum transfer

Double ionisation of helium in the perturbative regime has been explored in a kinematically complete collision experiment using 100 MeV/u C"6"+ ions. Different ionisation mechanisms are identified by inspecting the angular distribution of the electrons as a function of the momentum transfer q to the target by the projectile. For q<1.2 a.u., both electrons are distributed uniformly in the plane perpendicular to the projectile axis, and distinct similarities with photoionisation are identified. For q>1.2 a.u., the faster electron resulting from a binary encounter with the projectile is emitted along the direction of momentum transfer, while the other electron is distributed uniformly. Experimental data are compared with various model calculations based on the Bethe-Born approximation with shake-off. Surprisingly, the effect of the final state interaction is found to depend decisively on the choice of the initial state wave function. (orig.)Available from TIB Hannover: RO 801(99-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Electron bremsstrahlung in collisions of 223 MeV/u He-like uranium ions with gaseous targets

The bremsstrahlung process in the domain of strong Coulomb fields has been investigated for N_2 and Ar target electrons colliding with He-like uranium ions at 223 MeV/u. The doubly differential cross sections for bremsstrahlung were measured at the laboratory observation angles of 48 , 90 , and 132 . Substantial discrepancies were found between the experimental cross secions and the first order Born approximation calculations. The reported data provide a new testing ground for non-perturbative treatment of the coupling between radiation and matter in the presence of strong fields. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Exclusive studies of neutron and charged particle emission in collisions of "1"9"7Au+"1"9"7Au at 400 MeV/nucleon

We present data on collective flow of neutrons in collisions of "1"9"7Au+"1"9"7Au at 400 MeV/nucleon. The azimuthal distribution about the beam axis is investigated with respect to the reaction plane as determined from light charged particles. The 'squeeze-out' of neutrons, perpendicular to the reaction plane, is observed for the first time. Quantitative agreement to a high level of accuracy is found between the behaviour of neutrons and hydrogen ions. (orig.)Accepted for publication by Phys. Rev. Lett.SIGLEAvailable from TIB Hannover: RO 801(93-60) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Energy dependence of collective flow of neutrons and charged particles in "1"9"7Au+"1"9"7Au collisions

Our contribution focusses on one particular aspect of collective flow of nuclear matter: the so-called ''squeeze-out'', i.e. the preferential emission of mid-rapidity particles perpendicular to the reaction plane. The data were taken for the system "1"9"7Au + "1"9"7Au at 400, 600 and 800 MeV/u. We cover two topics, the comparison of neutrons and protons, and the bombarding energy dependence of the neutrons' squeeze-out. (orig.)Available from TIB Hannover: RO 801(94-02) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman