Ion-atom Collisions Research Articles

Agreement of Experiment and Theory on the Single Ionization of Helium by Fast Proton Impact.

Even though the study of ion-atom collisions is a mature field of atomic physics, large discrepancies between experiment and theoretical calculations are still common. Here we present experimental results with high momentum resolution on the single ionization of helium induced by 1-MeV protons, and we compare these to theoretical calculations. The overall agreement is strikingly good, and even the first Born approximation yields good agreement between theory and experiment. This has been expected for several decades, but so far has not been accomplished. The influence of projectile coherence effects on the measured data is briefly discussed in terms of an ongoing dispute on the existence of nodal structures in the electron angular emission distributions.

Angle-differential observation of plasmon electrons in the double-differential cross-section spectra of fast-ion-induced electron ejection fromC60

We report on the measurement of double-differential distribution of soft electron emission from ${\text{C}}_{60}$ fullerene, induced by a fast-moving Coulomb field of 76 MeV energy bare fluorine ions. A broad ``plasmon-electron'' peak, riding on the Coulomb-ionization continuum, is observed due to the deexcitation of the giant dipole plasmon resonance state in ${\text{C}}_{60}$. The angular distribution of the plasmon electrons goes through a dip around ${90}^{\ensuremath{\circ}}$, which is contrary to that observed in ion-atom collisions measured in situ, indicating the alignment of the induced dipole moment along the projectile beam direction. A model based on the photoelectron angular distribution which is modified due to the ion-induced postcollisional interaction provides an excellent agreement with the observed asymmetric distribution. The distribution smoothly changes from a dip at ${90}^{\ensuremath{\circ}}$ to a peak with the variation of ejected electron energy indicating transition from a collective plasmon behavior of the whole system to a single ion-atom interaction. The single-differential cross section was also derived, which preserves the signature of the collective excitation.

Simulation of Collisions of Ions with Atoms by the PIC–MC Method. Comparative Estimates

Monte Carlo models which simulate ion-atom collisions are considered. Efficient models for calculating the time between collisions are proposed which take into account the velocity dependence of the cross sections and also the probability distribution of the velocities of the ions and the probability distribution of the angles after a collision. The simulation results are compared with theoretical values of the drift velocity of the ions.

Effect of electron-nuclei interaction on internuclear motions in slow ion-atom collisions

The electron-nuclei interaction affects the internuclear motion in slow ion-atom collisions, which in turn affects theoretical results for the cross sections of various collision processes. The results are especially sensitive to the details of the internuclear dynamics in the presence of a strong isotope effect on the cross sections, as is the case, e.g., for the charge transfer in low-energy collisions of ${\text{He}}^{2+}$ with H, D, and T. By considering this system as an example, we show that internuclear trajectories defined by the Born-Oppenheimer (BO) potential in the entrance collision channel, which effectively accounts for the electron-nuclei interaction, are in much better agreement with trajectories obtained in the ab initio electron-nuclear dynamics approach [R. Cabrera-Trujillo et al., Phys. Rev. A 83, 012715 (2011)] than the corresponding Coulomb trajectories. We also show that the use of the BO trajectory instead of the Coulomb trajectory in the calculations of the charge-transfer cross sections within the adiabatic approach improves the agreement of the results with ab initio calculations.

Separation and solid angle correction of the metastable 1s2s2p 4P Auger yield produced in ion-atom collisions using the biased as cell technique: A tool for the determination of the population mechanisms

SynopsisWe demonstrate an experimental approach to the solid angle correction needed for the metastable 1s2s2p 4P state obtained in ion-atom collisions with gaseous targets. By applying a small bias voltage VGC on the target gas cell, the 4P contributions are separated into two peaks one arising from inside (which is shifted by e VGC) and the other outside the gas cell which is unshifted. Using SIMION we compute the correction in each case and perform a consistency check on our approach.

Radiative double electron capture by bare ions in collisions with gas targets

SynopsisRadiative double electron capture (RDEC) is a fundamental atomic process in ion-atom collisions, in which two electrons are captured to bound states of the projectile with the simultaneous emission of a single photon. To date, RDEC has been successfully measured only in collisions of bare O8+ and F9+ ions with thin-foil carbon targets. In this work we report progress on investigating RDEC in collisions with gas targets.

A dynamic ion-atom hybrid trap for high-resolution cold-collision studies

SynopsisTo push the frontier of studying ion-atom cold collisions, we present a new technique to precisely control collision energies in a hybrid trap setup.

Fraunhofer-type diffraction patterns of matter-wave scattering of projectiles: Electron transfer in energetic ion-atom collisions

Fraunhofer-type diffraction patterns of matter-wave scattering of projectiles: Electron transfer in energetic ion-atom collisions

Time-depending screening effects in relativistic calculations of electronic quantum dynamics in ion-atom collisions

Time-depending screening effects in relativistic calculations of electronic quantum dynamics in ion-atom collisions

Angular differential cross sections for double and single capture in fast ion-atom collisions

SynopsisWe investigate angular differential cross sections for double-electron and single-electron capture in ion- atom collisions for the intermediate and high energy region. We see the diffraction pattern in the spectrum of differential cross sections in the high energy range, i.e. another peak at 0.75 mrad in addition to Thomas peak at 0.47 mrad have been observed.

Impact of Debye plasmas environments on He-like ions and He-atom collisions

SynopsisThe impact of Debye plasmas on the electron capture and ionization process is investigated in multiply charged He-like ion (Li+, Be2+, B3+, C4+, N5+, O6+) and He atom collisions.

Double differential electron emission in ionization of Coronene by fast ions

SynopsisWe present the absolute differential electron emission cross section of coronene under fast bare O-ion impact. The results show some features which cannot be explained by simple ion-atom type collision result. The difference of the energy and angular distribution data with that for CH4 and Ne may indirectly indicate the influence of collective excitation. We have performed the CB1 calculation for comparison.

Fast electron emission in multiply charged ion-atom collisions at intermediate energies

SynopsisIn the present work we show electron spectra from Siq+ on H2 and He targets for projectile energies within the range 2.7 – 7 MeV for several emission angles. We discuss our results based on the picture of quantum interferences between the Short and Long range-projectile potential interactions in the emission of target electrons. Quantum mechanical CDW and CDW-EIS approximations are compared with present results.

Two- and many-body effects in cation emission from H2O molecules by O+ impact at keV energies: Similarities between ionization of atoms and proton emission from molecules

SynopsisWe demonstrate that energy and angle differential emission yields of fragment ions provide valuable information about the collisions of keV energy ions and molecules. For proton fragments, originating from larger molecules, there are striking similarities to the spectra of electrons emitted in fast ion-atom collisions.

Primary processes: from atoms to diatomic molecules and clusters

This article presents a short review of the main progresses achieved at the GANIL facilities during the last thirty years in the field of ion-atom and ion-diatomic molecule collisions. Thanks to the wide range of projectile energies and species available on the different beam lines of the facility, elementary processes such as electron capture, ionization and excitation have been extensively studied. Beside primary collision mechanisms, the relaxation processes of the collision partners after the collision have been another specific source of interest. Progresses on other fundamental processes such as Young type interferences induced by ion-molecule collisions or shake off ionization resulting from nuclear beta decay are also presented.

Full quantum study of non-radiative inelastic processes in lithium–helium ion–atom collisions★

Full quantum study of non-radiative inelastic processes in lithium–helium ion–atom collisions★

Multi-element readout of structured HPGe-detectors for high-resolution x-ray spectroscopy using CUBE-preamplifiers

Very recently we have shown that CUBE-preamplifiers developed by XGLab s.r.l. can be used for the readout of single elements of thick structured planar HPGe- and Si(Li)-detectors produced by SEMIKON [1]. In this paper we will present the results of a simultaneous multi-element readout of structured detectors using the same preamplifiers for measuring high-energy x-rays (more than 100 keV) with a comparable energy resolution as for the single-element readout. Several high-purity germanium detectors (HPGe-detectors) with different position sensitive structures on one detector contact have been used for the first tests. In addition to that we have modified an existing 16-pixel HPGe-polarimeter from GSI-Darmstadt with the new readout. The detector elements (7 mm × 7 mm each, arranged in a 4 × 4 matrix) are connected to CUBE-preamplifiers used in pulse-reset mode. The technological progress achieved with this detector system resulting in a significant improved energy resolution will contribute a lot to much more precise polarization measurements of x-rays emitted from atom-ion collisions which are part of the physics program of the SPARC collaboration (Stored Particles Atomic Physics Research Collaboration) at GSI and the future FAIR accelerator facility (Facility for Antiproton and Ion Research).

Atomic Physics with Accelerators: Projectile Electron Spectroscopy (APAPES)

The new research initiative APAPES (http://apapes.physics.uoc.gr/) has already established a new experimental station with a beam line dedicated for atomic collisions physics research, at the 5 MV TANDEM accelerator of the National Research Centre "Demokritos" in Athens, Greece. A complete zero-degree Auger projectile spectroscopy (ZAPS) apparatus has been put together to perform high resolution studies of electrons emitted in ion-atom collisions. A single stage hemispherical spectrometer with a 2-dimensional Position Sensitive Detector (PSD) combined with a doubly-differentially pumped gas target will be used to perform a systematic isoelectronic investigation of K-Auger spectra emitted from collisions of preexcited and ground state He-like ions with gas targets using novel techniques. Our intention is to provide a more thorough understanding of cascade feeding of the 1s2s2p 4P metastable states produced by electron capture in collisions of He-like ions with gas targets and further elucidate their role in the non-statistical production of excited three-electron 1s2s2p states by electron capture, recently a field of conflicting interpretations awaiting further resolution. At the moment, the apparatus is being completed and the spectrometer will soon be fully operational. Here we present the project progress and the recent high resolution spectrum obtained in collisions of 12 MeV C4+ on a Neon gas target.

Measurement of the low-energyNa+−Natotal collision rate in an ion-neutral hybrid trap

We present measurements of the total elastic and resonant charge-exchange ion-atom collision rate coefficient $k_\mathrm{ia}$ of cold sodium (\ce{Na}) with optically-dark low energy \ce{Na+} ions in a hybrid ion-neutral trap. To determine $k_\mathrm{ia}$, we measured the trap loading and loss from both a \ce{Na} magneto-optical trap (MOT) and a linear radio frequency quadrupole Paul trap. We found the total rate coefficient to be $7.4 \pm 1.9 \times 10^{-8}$ cm$^3$/s for the type I \ce{Na} MOT immersed within an $\approx 140$ K ion cloud and $1.10 \pm 0.25 \times 10^{-7}$ cm$^3$/s for the type II \ce{Na} MOT within an $\approx 1070$ K ion cloud. Our measurements show excellent agreement with previously reported theoretical fully quantal \textit{ab initio} calculations. In the process of determining the total rate coefficient, we demonstrate that a MOT can be used to probe an optically dark ion cloud's spatial distribution within a hybrid trap.

Micron X-ray computed tomography based on micro-particle-induced X-ray emission

Particle-induced X-ray emission (PIXE) is a phenomenon of atomic inner shell ionization and characteristic X-ray emission due to ion-atomic collisions. The intensity of continuous X-rays in the PIXE energy spectrum is much lower than that of characteristic X-rays. Therefore, PIXE can be used as a semi-monochromatic X-ray source. Furthermore, PIXE produced by a heavily charged particle beam with a diameter of several micrometers (micro-PIXE) can be used as a monochromatic X-ray point source for Xray computed tomography (CT) to investigate internal structures of objects <1 mm. We developed micron X-ray CT based on micro-PIXE with a spatial resolution of about 4 μm. Because the photoelectric effect cross-section is proportional to the fifth power of the atomic number, the distributions of small amounts of heavy elements can be investigated using this CT technique, and the element can be identified using its absorption edge. We applied this CT to observe the internal structure of hair, a head of an ant, and Drosophila. We were able to identify the medulla configuration and cortex of the hair, and the mandibular glands, pharynx, and brain in the ant head. We confirmed a high Mn concentration in the mandibular glands. We used a contrast agent to visualize the internal organs of Drosophila. Furthermore, we applied this CT to research clay particles contaminated by the Fukushima Dai-ichi nuclear accident and confirmed that cesium atoms were distributed on the surfaces of clay particles.