Radiative processes studied for bare uranium ions in collisions with H 2 (original) (raw)
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Electron- and Proton-Impact Excitation of Hydrogenlike Uranium in Relativistic Collisions
Physical Review Letters, 2013
The K shell excitation of H-like uranium (U 91þ) in relativistic collisions with different gaseous targets has been studied at the experimental storage ring at GSI Darmstadt. By performing measurements with different targets as well as with different collision energies, we were able to observe for the first time the effect of electron-impact excitation (EIE) process in the heaviest hydrogenlike ion. The large finestructure splitting in H-like uranium allowed us to unambiguously resolve excitation into different L shell levels. State-of-the-art calculations performed within the relativistic framework which include excitation mechanisms due to both protons (nucleus) and electrons are in good agreement with the experimental findings. Moreover, our experimental data clearly demonstrate the importance of including the generalized Breit interaction in the treatment of the EIE process.
Multiple ionization and collision dynamics in high-energy uranium-rare gas collisions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1989
The multiple ionization of rare gas target atoms in collisions with MeV/u highly-charged heavy ions was investigated systematically in a projectile energy (EP) regime between 1.4 and 420 meV/u. The absolute cross sections u(4) for the production of Ar recoil-ions with charge state 4 decrease smoothly with E, for 4 I 8, whereas a distinct maximum in the E,-dependence can be observed for higher 4. Furthermore. for 1.4 MeV/u U"+ and 5.9 MeV/u U65' Impact on Ne. a new experimental technique was applied allowing the simultaneous determination of 4 and of the transverse (with respect to the beam axis) recoil-ion momentum ~a L. From the good agreement of these differential absolute cross sections with the results of n-body classical trajectory Monte Carlo (nCTMC) calculations we conclude that the trajectories of the heavy nuclei are influenced considerably by the interaction with the target electrons as has been predicted by theory.
X-ray transitions studied for decelerated bare and H-like uranium ions at the ESR electron cooler
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
Here we report on X-ray spectra induced by spontaneous capture of free electrons into decelerated bare-and hydrogen-like uranium ions which we measured recently at the cooler section of the ESR storage ring. The most intense lines observed in spectra can be attributed to direct transition of electrons into the K shell of the projectile ions and to characteristic L ! K (Lya) transitions. Radiative recombination lines into the K shell of bare and H-like uranium can be exploited for measuring the two-electron contribution to the ground state binding energy in helium-like uranium. The goal is to probe for high-Z ions bound-state QED corrections which are of the order of a 2 . Besides the dominant characteristic L ! K transitions, the strongly reduced Bremsstrahlung (due to the low cooler voltage applied to the decelerated ions) allowed us to observe for the very first time RR transitions into the L shell as well as the balmer radiation located at the low-energy part of the spectra.
Radiative Electron Capture Studied for Bare, Decelerated Uranium Ions
Physica Scripta, 2001
By applying the deceleration technique for bare uranium ions at the ESR storage ring we studied the Radiative Electron Capture process in collisions with low-Z target atoms. This allowed us to extend the current information about the time-reversed photoionization process of highly-charged heavy ions to much lower energies than those accessible for neutral heavy elements in the direct reaction channel. The angular di¡erential data obtained prove theoretical predictions that at high-Z higher-order multipole contributions and magnetic corrections play an important role even at energies close to the threshold.
H(2s)formation inH+-H and H-H collisions
Physical Review A, 1980
Cross sections for metastable H(2s) formation by electron capture in H+-H(1s) collisions and by excitation in H(1s)-H(ls) collisions have been measured over the energy range 1.9-92 keV. A fast beam of H+ ions or H(ls) atoms was passed through a tungsten-tube-furnace target which contained thermally dissociated hydrogen. Fast metastable H(2s) atoms formed by collisions in the target were detected downstream using electric field quenching and Lyman-a photon-counting techniques. The present values are normalized at 24.5 keV to the average value of three previous indeyendent measurements of the H(2s) formation cross section in H+-H collisions which agree to within 20%. Measured cross sections for both H-H and H-H collisions contain only one maximum, in contrast with certain theoretical predictions. For H+-H the low-energy data are in good agreement with theoretical results based on a multistate molecular treatment of the collision. Above 75 keV the H+-H data agree with the Born approximation cross sections. Close-coupling pseudostate predictions lack overall detailed agreement with the present results, although the maximum in the cross section is reproduced well. High-energy (E & 15 keV) coupled-state calculations using a scaled hydrogenic two-center expansion are in good accord with the data. For H-H collisions all theoretical treatments are in poor accord with the present experimental results. Above 40 keV the measured H-H cross section is inversely proportional to the impact energy. This E energy dependence is in agreement with high-energy theoretical predictions. However, above 10 keV the Born approximation predicts structure in the cross section due to simultaneous excitation of the projectile and target which is not observed. The present results are compared with previous experimental determinations, and discrepancies are found to exist.
Multiple ionisation of rare gases by high-energy uranium ions
Journal of Physics B: Atomic, Molecular and Optical Physics, 1988
Multiple ionisation cross sections u (q) for the production of recoil ions in charge state q by 120 MeV U-' U90+ impact have been measured for Ne, Ar and Kr targets using a recoil-ion-projectile-electron triple-coincidence technique. The data are compared with previously measured cross sections for U-ion impact in the projectile energy (E,) range from 1.4 to 420 MeV U-'. For low recoil-ion charge states a (q) decreases over the whole E , range somewhat more slowly than l/E,, whereas for higher recoil-ion charge states a (q) reaches a maximum at about 10-15 MeVu-'. The data are nicely described by parameter-free n-body Classical Trajectory Monte Carlo (~C T M C) calculations. The calculations indicate the importance of accounting for the Auger events in the description of the multiple ionisation process. Because of the smooth E , dependence of "(4) towards high E , , the development of a recoil-ion source using a primary U-ion beam in a storage ring for the production of high charge state recoil-ions appears to be feasible.
Physical Review A, 2001
We have investigated ionization mechanisms in fast ion-atom collisions by measuring the low-energy electron emission cross sections in a pure three-body collision involving bare carbon ions (vϭ6.35 a.u.) colliding with atomic hydrogen targets. The measurements have also been extended to molecular hydrogen and helium targets. In this paper we provide the energy and angular distributions of double differential cross sections of low-energy electron emission for atomic hydrogen targets. The Slevin rf source with a high degree of dissociation was used to produce the atomic H target. It is found that the two-center effect has a major influence on the observed large forward-backward angular asymmetry. A detailed comparison is presented with calculations based on the continuum distorted-wave ͑CDW͒ and CDW-EIS ͑eikonal initial-state͒ approximations. Both the continuum distorted-wave calculations provide a very good understanding of the data, whereas the first Born calculation predicts almost symmetric forward-backward distributions that do not agree with the data. The two-center effect is slightly better represented by the CDW calculations compared to the CDW-EIS calculation. The total cross sections are, however, in good agreement with the theories used. The results for molecular hydrogen and helium will be discussed in the following paper.
Journal of Physics B-atomic Molecular and Optical Physics, 2004
The radiative charge exchange processes in H+ + H(1s) and He+(1s) + H(1s2) collisions at intermediate ion-atom impact velocities were treated in this paper from a spectroscopic aspect as new sources of UV and VUV emission. These processes were characterized by the cross-section spectral densities. In the case of hydrogen the corresponding spectral density was calculated for the wavelength lgr and impact velocity v in the ranges 1.823 nm les lgr les 217.537 nm and 0.141v0 les v les 1.414v0 where v0 is the atomic unit velocity. Based on these calculations the photon fluxes, generated due to the interaction of weakly ionized low pressure hydrogen plasma with H+ ion beams, were estimated. It was shown that these fluxes in the UV and VUV domain were strong enough for the spectroscopic measurement. In the case of helium the photon fluxes were estimated in the range lgr > 30 nm. It was found that they are smaller than those in the case of hydrogen but still at a substantial level.