T. Ludziejewski

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 and Ar target electrons colliding with He-like uranium ions at . The differential cross sections for bremsstrahlung were measured at laboratory observation angles of , , and . Substantial discrepancies were found between the experimental cross sections 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.

Projectile excitation and ionization in relativistic ion-atom collisions

Abstract K-shell ionization and excitation is studied for high-Z one-and two-electron ions in relativistic encounters with low-Z targets. For ionization, the data obtained for solid and gaseous targets are compared in detail with the predictions of first order perturbation theory. On the basis of the most recent experimental results, the systematic deviation from first order perturbation theory as observed recently for high-Z ions cannot be confirmed. Moreover, special emphasis is given to a dedicated experiment where projectile excitation has been studied in encounters of heavy one-and two-electron bismuth ions (Z = 83) with light solid targets. The measurement of the characteristic ground-state transitions in coincidence with the primary charge state allowed us to study the formation of excited projectile states via direct Coulomb excitation. In particular, due to the large fine-structure splitting, the excitation cross-sections for the various L-shell sublevels in H- and He-like bismuth could be determined separately. The results are compared with detailed relativistic calculations showing that for high-Z projectiles the magnetic interaction is of considerable importance at the considered collision energies.

The absorption-edge technique at the gas-jet target of the ESR

In a first pilot experiment the absorption-edge spectroscopy was applied at the gas-jet target of the ESR storage ring in order to measure the ground state transitions of H- and He-like gold-ions. The aim of this experiment was to test the potential of this technique for a precise study of QED-effects in high Z ions at the storage ring.

Two-photon decay in strong central fields observed for the case of He-like gold

Abstract The photon energy differential shape of the second order matrix element for the two-photon (2E1) decay of the 1s2s 1 S 0 level in He-like gold has been measured. The results are in agreement with a recent fully relativistic calculation. The corresponding 2E1 matrix element deviates from those in lighter He-like systems due to the strong central field in a heavy two-electron ion.

First experiment with decelerated bare uranium ions conducted at the ESR storage ring

The deceleration capabilities of the ESR have been used for the first time in a dedicated ground state QED experiment conducted at the gasjet target of the ring. By decelerating bare uranium ions from 358 MeV/u down to energies of as low as 49 MeV/u, X-ray spectra have been obtained which provide an abundant yield of characteristic X-ray transitions. The experiment demonstrates that, by choosing the appropriate beam energy and gasjet target, almost all excited projectile states can be selectively populated. Moreover, the experiment provides the first data for beam lifetimes of stored decelerated high-Z ions. Such data are essential for the design of future experiments dealing with decelerated ion beams far below 50 MeV/u.

Interference between electric and magnetic amplitudes for K shell excitation of high-Z H-like projectiles

Abstract We report an investigation of projectile K shell excitation for high- Z ions in relativistic ion-atom collisions. For the case of H-like Bi, the excitation process is unambiguously identified by observing the radiative decay of the excited levels to the vacant 1s shell, in coincidence with ions that did not undergo any charge exchange in the reaction target. The results are compared with detailed relativistic calculations, showing that the magnetic interaction is of considerable importance for the K shell excitation process in high- Z ions. For excitation to the L shell sublevels, the experimental data confirm that the magnetic part of the Lienard-Wiechert interaction must be added coherently with the electric part leading to a significant reduction of the K shell excitation cross section.

Excitation of high-Z one- and two-electron ions in relativistic collisions with gaseous targets

Abstract Progress in the studies of ground state excitation of heavy hydrogen-like and helium-like ions in relativistic collisions with atoms is reported. In particular the recent results obtained in experiments carried out at the internal gas-jet target of the ESR Storage Ring at GSI-Darmstadt are presented. Special emphasis is given to the sensitivity of the measured state selective cross sections to the magnetic effects occurring in relativistic heavy-ion–atom collisions.

Measurement of the spectral shape for the two-photon decay in heliumlike gold

Progress on a measurement of the spectral distribution of the two-photon decay of the 1s2s 1S0 level in the strong central fields of heavy heliumlike ions is reported. A measurement of the exact shape of the continuous spectrum of the two-photon decay in heavy heliumlike ions provides a sensitive test of the details of the complete structure of a heliumlike system. In our experiment at GSI, a beam of 106.6 MeV/u Au77+ ions was excited by a thin Aluminum foil and the subsequent decays were observed in an array of Ge(i) detectors.

Emission of De-excitation x-rays from radiative electron capture into bare projectiles as the inverse of two-step photoionization

In relativistic collisions between bare high-Z ions and low-Z target atoms, electron capture into the ground and excited projectile states is almost completely caused by the time-reserved photoelectric effect, i.e. radiative electron capture. A study of the REC process into bare high-Z can therefore be utilized for the investigation of the photoelectric effect. In this paper we present data for the inverse of the two-step photo-ionization process, which were obtained by measuring the angular distribution of the Lyα1 (2p3/2 → 1s1/2) de-excitation photons induced by REC into the 2p3/2 state of initially bare high-Z ions. The anisotropic emission, revealed by the experiments, demonstrates that the population of the magnetic substates by REC in fast collisions deviates strongly from the statistical one, and that it must lead to a strongly polarized Lyα1-radiation.