A. Warczak

Observation of hydrogenlike and heliumlike krypton spectra

Hydrogenlike and heliumliken=2→n=1 lines in Kr have been produced and studied for the first time. HydrogenlikeL y α lines have been observed and the fine structure interval has been determined. The absolute energy of the1P1,3P2,3P1 lines of heliumlike Kr have been measured and compared to Multiconfigurational Dirac-Fock Calculations.

Applications of position sensitive germanium detectors for X-ray spectroscopy of highly charged heavy ions

The spectroscopy of atomic transitions in the hard X-ray regime above 15 keV utilizing position-sensitive solid state detectors is discussed. Special emphasis is given to the current detector developments for X-ray spectroscopy of heavy ions at the ESR storage ring where applications for precision spectroscopy as well as for polarization studies are of particular interest. For both cases, the advantages and new possibilities which are opened up by position and energy resolving solid state detectors are illustrated by the presentation of first experiments.

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.

Precision tests of QED in strong fields: experiments on hydrogen- and helium-like uranium

In this contribution, we present an experimental study carried out at GSI Darmstadt devoted to investigation of quantum electrodynamical (QED) effects for the ground states in hydrogen- and helium-like uranium. In the experiment, X-ray spectra following radiative recombination of free electrons with bare and H-like uranium ions (U92+, U91+) were measured at the electron cooler of the ESR storage ring. Utilizing clean and favorable experimental conditions present at the electron cooler, we were able to obtain very accurate values for the ground-state binding energies from the observed X-ray transitions. When compared with theory, our results provide the most stringent test of bound-state QED for one- and two-electron systems in the strong-field regime.

Deviation from first-order perturbation theory observed at intermediate relativistic velocities for the ionisation of highly-charged heavy projectiles

Projectile K-shell ionization cross sections were measured for 80-200 MeV u-1 H- and He-like Bi ions on thin C, Al and Ni targets. The results are compared with predictions of first-order perturbation theories, RSCA and PWBA, as well as with experimental results published for Xe and U ions at similar ratios eta of projectile velocity to K-shell electron velocity. All experimental data lie a factor of 1.5 above theory for 0.6< eta <1.5.

Ground state transitions in one- and two-electron Bi projectiles

Abstract By using segmented solid state X-ray detectors and applying X-ray/charge-state selective particle coincidences, the ionic structures of 83 Bi 82+ and 83 Bi 81+ have been studied separately at 82 MeV/u under single collision conditions. The high granularity of the Ge(i) X-ray detectors used allowed a partial Doppler correction for the X-ray events while maintaining a large total solid angle. An absoluute precision of K-transition energies of 10 −3 is feasible; the relative accuracy is better than 30 eV. The experimental values compare very well with the theoretical transition energies in H- and He-like Bi ions.

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.

Radiative double electron capture in heavy-ion atom collisions

Abstract Total cross sections for radiative double electron capture (RDEC) in collisions of fast highly charged ions with light target atoms were estimated. The applied method is based on the principle of detailed balance using the cross sections for the double photoionization process. Preliminary results of a dedicated RDEC experiment aiming at the observation of photons with twice the single REC photon energy, associated with double charge exchange, are discussed. Additionally, results of complementary measurements of double capture (without photon registration) by fully stripped U ions in collisions with C atoms at 295 MeV/u are presented. Here, a surprisingly enhanced cross section for double electron capture is found in accordance with observations reported in the literature.

Single and double electron capture in collisions of highly ionized, decelerated Ge ions with Ne

Experimental cross sections for non-radiative single and double electron capture from Ne target into decelerated H-like Ge ions at collision energies of (4-12) MeV u-1 are presented. The results are compared with theoretical calculations and an empirical scaling rule. Information concerning the impact parameter dependence of electron capture is extracted using classical trajectory Monte Carlo calculations.

Double-electron capture in relativistic U92+ collisions at the ESR gas-jet target

Abstract Total cross-sections for radiative single- and double-electron capture are measured in collisions of fast highly charged ions with light target atoms. Cross-sections for non-correlated double capture are in accordance with theoretical predictions. No significant line structure at twice the single K-radiative electron capture (K-REC) photon energy was observed. Angular distributions single K-REC photons associated with single- and double-charge exchange exhibit the same pattern. The corresponding REC lines are almost by a factor of two broader for double-charge exchange than in the single capture case.