184 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
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
Recommended from our members
Past millennium hydroclimate variability from Corsican pine tree-ring chronologies
Palaeoclimatic evidence is necessary to place the current warming and drying trends of the Mediterranean region in a longâterm perspective of preâindustrial variability. Annually resolved and absolutely dated climate proxies that extend back into medieval times are, however, limited to a few sites only. Here we present a network of long ring width chronologies from Pinus nigra treeâline sites in northern Corsica (France) that cohere exceptionally well over centuries and support the development of a single highâelevation pine chronology extending back to 974 CE. We apply various detrending methods to these data to retain highâtoâlow frequency ring width variability and scale the resulting chronologies against instrumental precipitation and drought observations to produce hydroclimate reconstructions for the last millennium. Proxy calibration and transfer are challenged by a lack of highâelevation meteorological data, however, limiting our understanding of precipitation changes in subâalpine treeâline environments. Our new reconstructions extend beyond existing records and provide evidence for lowâfrequency precipitation variability in the centralâwestern Mediterranean from 974â2016 CE. Comparison with a European scale drought reconstruction network shows that regional predictor chronologies are needed to accurately estimate longâterm hydroclimate variability on Corsica
Hyperspherical partial wave calculation for double photoionization of the helium atom at 20 eV excess energy
Hyperspherical partial wave approach has been applied here in the study of
double photoionization of the helium atom for equal energy sharing geometry at
20 eV excess energy. Calculations have been done both in length and velocity
gauges and are found to agree with each other, with the CCC results and with
experiments and exhibit some advantages of the corresponding three particle
wave function over other wave functions in use.Comment: 11 pages, 1 figure, submitted to J. Phys B: At. Mol. Opt. Phys; v2 -
revised considerably, rewritten using ioplatex clas
State-resolved valence shell photoionization of Be-like ions: experiment and theory
High-resolution photoionization experiments were carried out using beams of
Be-like C, N, and O ions with roughly equal populations of
the S ground-state and the P manifold of metastable components. The
energy scales of the experiments are calibrated with uncertainties of 1 to 10
meV depending on photon energy. Resolving powers beyond 20,000 were reached
allowing for the separation of contributions from the individual metastable
P, P, and P states. The measured data compare
favourably with semi-relativistic Breit-Pauli R-matrixComment: 23 figures and 3 table
Measurements of proton-induced reactions on ruthenium-96 in the ESR at GSI
8th International Conference on Nuclear Physics at Storage Rings Stori11, October 9-14, 2011 Laboratori Nazionale di Frascati, Italy.
Storage rings offer the possibility of measuring proton- and alpha-induced reactions in inverse kinematics. The combination of this approachwith a radioactive beamfacility allows, in principle, the determination of the respective cross sections for radioactive isotopes. Such data are highly desired for a better understanding of astrophysical nucleosynthesis processes like the p-process. A pioneering experiment has been performed at the Experimental Storage Ring (ESR) at GSI using a stable 96Ru beam at 9-11 AMeV and a hydrogen target. Monte-Carlo simulations of the experiment were made using the Geant4 code. In these simulations, the experimental setup is described in detail and all reaction channels can be investigated. Based on the Geant4 simulations, a prediction of the shape of different spectral components can be performed. A comparison of simulated predictions with the experimental results shows a good agreement and allows the extraction of the cross section
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
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
- âŠ