Magnetic Sublevel Population Studied for H- and He-like Uranium in Relativistic Ion–Atom Collisions (original) (raw)
Physical Review A, 2011
We have measured the alignment of the L-shell magnetic-substates following the K-shell excitation of hydrogen-and helium-like uranium in relativistic collisions with a low-Z gaseous target. Within this experiment the population distribution for the L-shell magnetic sublevels has been obtained via an angular differential study of the decay photons associated with the subsequent de-excitation process. The results show a very distinctive behavior for the H-and He-like heavy systems. In particular for K → L excitation of He-like uranium, a considerable alignment of the L-shell levels was observed. A comparison of our experimental findings with recent rigorous relativistic predictions provides a good qualitative and a reasonable quantitative agreement, emphasizing the importance of the magnetic-interaction and many-body effects in the strong-field domain of high-Z ions.
Atoms
In this paper, we present an experimental and theoretical study of excitation processes for the heaviest stable helium-like ion, that is, He-like uranium occurring in relativistic collisions with hydrogen and argon targets. In particular, we concentrate on angular distributions of the characteristic Kα radiation following the K → L excitation of He-like uranium. We pay special attention to the magnetic sub-level population of the excited 1s2lj states, which is directly related to the angular distribution of the characteristic Kα radiation. We show that the experimental data can be well described by calculations taking into account the excitation by the target nucleus as well as by the target electrons. Moreover, we demonstrate for the first time an important influence of the electron-impact excitation process on the angular distributions of the Kα radiation produced by excitation of He-like uranium in collisions with different targets.
Physical Review A, 2013
Simultaneous ionization and excitation processes are studied for initially He-like uranium ions in collisions with xenon gaseous targets at relativistic energy, 220 MeV/u. The virtue of investigating the process of simultaneous excitation and ionization is that one electron ends up in the continuum, while the other electron ends up in a hydrogen-like final state. Experimentally, this process can be identified by observing the radiative decay of the excited levels in coincidence with ions that lost one electron (U 91+ ). In particular, owing to the large fine-structure splitting of H-like U, the angular distribution of photons for the simultaneous ionization and excitation into the different total angular momentum j = 1/2 and j = 3/2 states of the L shell is determined directly from the observed yields of Ly α1 and Ly α2 radiation at various observation angles. The experimental data show a progress for the dependence of the alignment on the collision impact parameter. It is shown that the current results confirm the theoretical predictions based on the independent-particle approximation and first-order perturbation, for which the simultaneous ionization and excitation processes occur at small impact parameter.
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.
Magnetic sublevel population in 1s-2p excitation of helium by fast electrons and protons
Journal of Physics B: Atomic, Molecular and Optical Physics, 2001
We report experimental and theoretical results for the magnetic sublevel population of the helium atom in collisions with fast (v i = 3-9 au) electrons and protons. Cross sections for excitation of magnetic sublevels with M = 0 and ±1 have been obtained using polarization measurements of emitted radiation in combination with differential cross sections. Calculations have been carried out using the expansion of the transition amplitude in the Born series over the projectile-target interaction through the second order. Results of calculations are in agreement with experimental data. We find that the particle-antiparticle Z ± difference exceeds the statistical error of measurement up to collision velocities v i ≈ 6 au for excitation of sublevels with M = 0.
Electron bremsstrahlung in collisions of 223 MeV/ u He-like uranium ions with gaseous targets
Journal of Physics B: Atomic, Molecular and Optical Physics, 1998
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 differential cross sections for bremsstrahlung were measured at laboratory observation angles of 48 • , 90 • , and 132 • . 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. † † Permanent address: So ltan Institute for Nuclear Studies,
Physical Review Letters, 2004
Radiative recombination transitions into the ground state of cooled bare and hydrogen-like uranium ions were measured at the storage ring ESR. By comparing the corresponding x-ray centroid energies, this technique allows for a direct measurement of the electron-electron contribution to the ionization potential in the heaviest He-like ions. For the two-electron contribution to the ionization potential of He-like uranium we obtain a value of 2248 ± 9 eV. This represents the most accurate determination of two-electron effects in the domain of high-Z He-like ions and the accuracy reaches already the size of the specific two-electron radiative QED corrections.
Selective population of the[1s2s]S01and[1s2s]S13states of He-like uranium
Physical Review A, 2006
The formation of the ͓1s2s͔ S states in heliumlike uranium ͑U 90+ ͒ has been studied in relativistic collisions of initially lithiumlike uranium ͑U 89+ ͒ ions with N 2 target molecules. By measuring projectile x-ray emission in coincidence with projectile ionization, a strong selectivity for the formation of the ͓1s2s͔ S states in heliumlike uranium is observed. This selectivity is found to be unaffected by the subsequent rearrangement of the atomic orbitals involved. By measuring the photon emission associated with the decay of the ͓1s2s͔ 1 S 0 and the ͓1s2s͔ 3 S 1 substates, we obtain for their relative population probabilities a ratio of close to 1. This finding deviates considerably from the assumption of a statistical distribution 2J +1.
Projectile excitation and ionization in relativistic ion-atom collisions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1997
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.
2020
136 EXPERIMENTAL STUDIES OF THE NUCLEAR-PHYSICAL CHARACTERISTICS OF THE EXTENDED URANIUM TARGET IRRADIATED BY RELATIVISTIC PROTONS, DEUTRONS AND C NUCLEI A.A. Zhadan, V.V. Sotnikov, V.A. Voronko, A.A. Baldin, S.I. Tyutyunnikov, O.V. Bukhal, K.V. Husak, I.V. Zhuk, P. Zhivkov National Science Center “Kharkov Institute of Physics and Technology”, Kharkiv, Ukraine; Joint Institute for Nuclear Research, Dubna, Russia; Joint Institute for Power and Nuclear Research – SOSNY, Minsk, Belarus; Institute for Nuclear Research and Nuclear Energy, Sofia, Bulgaria E-mail: zhadan@kipt.kharkov.ua