160 research outputs found
Electron gas polarization effect induced by heavy H-like ions of moderate velocities channeled in a silicon crystal
We report on the observation of a strong perturbation of the electron gas
induced by 20 MeV/u U ions and 13 MeV/u Pb ions channeled in
silicon crystals. This collective response (wake effect) in-duces a shift of
the continuum energy level by more than 100 eV, which is observed by means of
Radiative Electron Capture into the K and L-shells of the projectiles. We also
observe an increase of the REC probability by 20-50% relative to the
probability in a non-perturbed electron gas. The energy shift is in agreement
with calculations using the linear response theory, whereas the local electron
density enhancement is much smaller than predicted by the same model. This
shows that, for the small values of the adiabaticity parameter achieved in our
experiments, the density fluctuations are not strongly localized at the
vicinity of the heavy ions
Differential energy measurement between He- and Li-like uranium intra-shell transitions
We present the first clear identification and highly accurate measurement of
the intra-shell transition 1s2p\, ^3P_2 \to 1s2s\, ^3S_1 of He-like uranium
performed via X-ray spectroscopy. The present experiment has been conducted at
the gas-jet target of the ESR storage ring in GSI (Darmstadt, Germany) where a
Bragg spectrometer, with a bent germanium crystal, and a Ge(i) detector were
mounted. Using the ESR deceleration capabilities, we performed a differential
measurement between the 1s2p\, ^3P_2 \to 1s2s\, ^3S_1 He-like U transition
energy, at 4510 eV, and the 1s^22p\ ^2P_{3/2} \to 1s^22s\, ^2S_{1/2} Li-like
U transition energy, at 4460 eV. By a proper choice of the ion velocities, the
X-ray energies from the He- and Li-like ions could be measured, in the
laboratory frame, at the same photon energy. This allowed for a drastic
reduction of the experimental systematic uncertainties, principally due to the
Doppler effect, and for a comparison with the theory without the uncertainties
arising from one-photon QED predictions and nuclear size corrections
Subshell-selective x-ray studies of radiative recombination of ions with electrons for very low relative energies
Radiative recombination (RR) into the K shell and L subshells of U92+ ions interacting with cooling electrons has been studied in an x-ray RR experiment at the electron cooler of the Experimental Storage Ring at GSI. The measured radiative recombination rate coefficients for electron-ion relative energies in the range 0–1000 meV demonstrate the importance of relativistic effects. The observed asymmetry of the measured K-RR x-ray emission with respect to the cooling energy, i.e., zero average relative velocity (⟨vrel⟩=0), are explained by fully relativistic RR calculations. With our new approach, we show that the study of the angular distribution of RR photons for different relative energies opens new perspectives for detailed understanding of the RR of ions with cooling electrons in cold magnetized plasma
Observation of the 2p3/2 -> 2s1/2 intra-shell transition in He-like uranium
We present the first observation of the 1s2p 3P2 ? 1s2s 3S1 transition in
He-like uranium. The experiment was performed at the internal gas-jet target of
the ESR storage ring at GSI exploiting a Bragg crystal spectrometer and a
germanium solid state detector. Using the 1s2 2p 2P3/2 ? 1s2 2s 2S1/2
transition in Li-like uranium as reference and the deceleration capabilities of
the ESR storage rings, we obtained the first evaluation of the He-like heavy
ion intra-shell transition energy
Ion slowing down and charge exchange at small impact parameters selected by channeling: superdensity effects
CASInternational audienceIn two experiments performed with 20-30 MeV/u highly charged heavy ions (Pb56+, U91+) channeled through thin silicon crystals, we observed the original features of superdensity, associated to the glancing collisions with atomic rows undergone by part of the incident projectiles. In particular the very high collision rate yields a quite specific charge exchange regime, that leads to a higher ionization probability than in random conditions. X-ray measurements show that electrons captured in outershells are prevented from being stabilized, which enhances the lifetime of the projectile innershell vacancies. The charge state distributions and the energy loss spectra are compared to Monte-Carlo simulations. These simulations confirm, extend and illustrate the qualitative analysis of the experimental results
Mechanisms of K-vacancy production determined from the impact-parameter dependence of K x-ray production in 1.4-MeV/amu Kr + Ge collisions
Charge state dependence of characteristic x-ray emission under single collision conditions for 1.4 MeV/amu Cu ions
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