Peer-Review Publications

1992

T. Stöhlker, C. Kozhuharov, A. E. Livingston, P. H. Mokler, Z. Stachura, and A. Warczak
Radiative Electron-Capture into the K-Shell, L-Shell and M-Shell of Decelerated, Hydrogenic Ge Projectiles
Z. Phys. D, 23 :121 (June 1992)
Abstract:
Radiative Electron Capture (REC) in 4 to 12 MeV/u Ge^31+ —> H2 collisions has been studied using an X-ray/particle coincidence technique. This technique allowed a systematic investigation of K-shell REC as well as a separation of REC into the projectile L- and M-shells. The cross sections are discussed within a general scaling picture based on the reduced projectile velocity.

1991

T. Stöhlker, H. Geissel, H. Folger, C. Kozhuharov, P. H. Mokler, G. Münzenberg, D. Schardt, T. Schwab, M. Steiner, H. Stelzer, and K. Sümmerer
Equilibrium Charge State Distributions for Relativistic Heavy-Ions
Nucl. Instr. Meth. B, 61 :408 (October 1991)
Abstract:
Equilibrium charge-state distributions have been measured for 617.2 MeV/u Au and 758.2 MeV/u Xe projectiles traversing C, Al, and Pb targets. In all cases bare ions dominate the charge-state distributions as expected for such relativistic velocities. For both projectiles used, the Al target produced the largest fraction of bare ions. This result is in agreement with calculations and with measurements for uranium ions given in the literature. These first atomic physics measurements at the new SIS accelerator have been performed during commissioning of the fragment separator (FRS).
P. H. Mokler, T. Stöhlker, C. Kozhuharov, Z. Stachura, and A. Warczak
Radiative Electron-Capture - a Tool for Structure Studies of Heavy Few-Electron Ions
Z. Phys. D, 21 :197 (September 1991)
Abstract:
Radiative Electron Capture (REC) in collisions of hydrogenic germanium ions with hydrogen is measured for projectile energies between 4 and 12 MeV/u. Extrapolating the resulting centroid energies of the K-REC radiation to zero collision velocity the K-binding energy in helium-like germanium-ions is determined. The value compares well with the theoretical prediction. REC in atomic collisions is advertised as a spectroscopic tool for structure investigations of very heavy few-electron projectiles.
T. Stöhlker, P. H. Mokler, C. Kozhuharov, E. A. Livingston, and J. Ullrich
Capture of Quasi-Free Electrons into Highly Charged, Heavy Projectiles
Nucl. Instr. Meth. B, 56-7 :86 (May 1991)
Abstract:
In collisions between highly charged, heavy ions and light target atoms at adiabaticity parameters of 0.5 less-than-or-equal-to v2/u2 less-than-or-equal-to 0.75, resonant transfer and excitation (RTE) is an important charge-exchange process. Experiments for medium Z-ions are reviewed. Special emphasis is given to the competing radiative electron capture (REC) process. The general dependences of REC are discussed. In particular, we elucidate results obtained by the triple X-ray/X-ray/charge-changed particle coincidence technique for hydrogenic projectiles up to 36Kr35+ ions. With this method we could isolate a single RTE resonance, the 2s2p1P1 state, which stabilizes radiatively to the metastable 1s2s1S0 state. This state can only decay via two photon emission (2E1). Applying the triple coincidence technique we observed additional strong photon coincidences induced by cascades following REC into high projectile states.
T. Stöhlker, C. Kozhuharov, A. E. Livingston, P. H. Mokler, J. Ullrich, and B. Fricke
2-Photon Decay of the 1s2s S-1(0) State in Kr-36(34+) Produced by Resonant Transfer and Excitation
Z. Phys. D, 21 :S233 (March 1991)
Abstract:
The doubly excited 2s2p 1P1 level of Kr34+ populated via resonant transfer and excitation (RTE) feeds selectively the metastable 1s2s 1S0 state which can only decay via simultaneous emission of two photons to the ground state 1s2 1S0. X-ray/X-ray coincidence measurements in heavy ion-atom collisions enable the direct measurement of the spectral distribution of the two-photon decay in He-like ions. In addition, we observe strong photon cascades induced by radiative electron capture.

1990

A. Warczak, Z. Stachura, A. Szymanski, T. Stöhlker, C. Kozhuharov, A. E. Livingston, P. H. Mokler, and S. Reusch
Evidence for Resonant 2-Electron Capture and Excitation in Collisions of H-Like Ge with Ne
Phys. Lett. A, 146 :122 (May 1990)
Abstract:
Evidence for resonant two-electron capture and excitation, i.e. the time-recersed double Auger process with radiative stabilitization, was found by measuring coincidences between two K-X-rays of a heavy ion associated with its double charge exchange. Hydrogen-like Ge31+ ions with energies of 4.5-11.5 MeV/u were directed into a neon gas target. Contributions from the double non-resonant transfer and excitation process are also discussed.

1989

P. H. Mokler, S. Reusch, and T. Stöhlker
Heavy-Ion Beam Tailoring Using Dielectronic Recombination
Nucl. Instr. Meth. A, 278 :93 (May 1989)
Abstract:
For non-naked highly-charged heavy ions, dielectronic recombination (DR) can be the dominant electron capture process. Depending on the kind of a DR resonance involved, cross sections may reach values up to 10^2-18 cm^2 at the peak maximum. The widths of the DR resonances are typically <1 eV. Tuning a merged electron beam with an internal temperature typically - 0.1 eV to the DR resonance, a well defined narrow part can be cut out of the original "hot" primary ion beam by this charge-exchange process. The charge-changed new beam is pretty "cool" (DE/E=10^-5). Acase study for Ge^31+ +e=Ge^30+** (2P^2^1D_2) is given. Technical applications of DR beam tailoring techniques at heavy-ion storage rings will be discussed.
P. H. Mokler, S. Reusch, T. Stöhlker, R. Schuch, M. Schulz, G. Wintermeyer, Z. Stachura, A. Warczak, A. Müller, Y. Awaya, and T. Kambara
Resonant Transfer and Excitation in Swift, Heavy Few-Electron Projectiles
Rad. Eff. Def. Solids, 110 :39 (January 1989)