Heavy Ion Impact Research Articles

Secondary ions produced from condensed rare gas targets under highly charged MeV/amu heavy ion bombardment

Secondary ions produced from condensed rare gas targets are observed under MeV amu , highly charged, heavy ion impact. The intensities of the observed cluster ions decrease smoothly as the cluster sizes become large but show some discontinuities at particular sizes of cluster ions. This seems to be closely related to the stabilities of cluster ion structures. It is also noted that very few doubly charged or practically no triply/higher charged ions have been observed, in sharp contrast to that of some condensed molecular targets.

Secondary ions from condensed CH4 and NH3 targets under energetic highly charged ion impact-effects of chemical structures and reactivities

Secondary ions produced from condensed NH3 and CH4 molecules under MeV amu-1 heavy ion impact have been observed. Intensities of multiply charged atomic ions are found to depend upon the chemical structures of the parent molecules, while those of cluster ions seem to be influenced through the chemical reactivity of the parent molecules or collision products.

Electron excitation of hydrogenic targets in collisions with ions or atoms

A symmetric eikonal model is developed to study electron excitation of hydrogenic atoms by impact of heavy ions (composed of a nucleus and N electrons) at intermediate and high collision velocities. Differential cross sections are calculated for impact of He+ ions on H targets and compared with existing experimental data for formation of H(n=2) atoms. Total cross sections for collisions of singly (H+, He+, Li+) and doubly charged (He2+, Li2+) projectiles on H targets are also computed. A good representation of measurements is obtained for He+ ions. The role played by the spatial distribution of projectile electrons is analysed.

Energy sensitive detection of heavy ions with transition edge calorimeters

Status and results of a research project are reported, which aims at developing calorimetric low temperature detectors of heavy ions. The special conditions for the detection of energetic heavy ions are discussed. The response of an aluminium transition edge calorimeter, operated at about 1.5K, to the impact of heavy ions was investigated. The observed energy resolutions [Delta]E/E = 3.9 x 10[sup [minus]3] for 5.9 MeV/u [sup 208]Pb-ions, [Delta]E/E = 1.6 x 10[sup [minus]3] for 4.8 MeV/u [sup 58]Ni-ions and [Delta]E/E = 4.3 x 10[sup [minus]3] for 100 MeV/u [sup 20]Ne-ions are most probably not yet limited by the intrinsic detector resolution. The present results already represent an improvement over conventional solid state detectors and ionization chambers.

Ion track structure probed by plasma desorption mass spectrometry

Since the discovery of plasma desorption mass spectrometry by Torgerson [D.F. Torgerson, R.P. Skowronski and R.D. Macfarlane, Biophys. Res. Commun., 60(1974) 616], the method has mainly been used in mass spectrometric studies of bioorganic molecules. However, the ejecta in this electronic sputtering process have also been studied with the aim to gain information on the structure of the ion track formed in a solid by the incident fission fragment. In this paper such studies will be described. In particular, the ejection of large whole ionised organic molecules and the synthesis of fullerenes at the impact of a fast heavy ion on an organic solid will be discussed. Those two processes are connected to different parts of the ion track. Also, the ejection of light ions and damage cross sections will be discussed and are shown to give additional information on the time and space evolution of energy deposited in a fast ion track.

Giant radiation damage produced by the impact of heavy molecular ions onto silicon single crystal

The giant radiation damage imparted to single-crystalline silicon by the impact of Re 2(CO) 2 + at 140 keV is studied by conventional and high-resolution transmission electron microscopy. Evidence for damage produced by the correlated motion of the atoms initially forming the molecular ion is presented.

Multiple inner-shell ionization of target atoms by high-energy heavy-ion impact

Multiple inner-shell ionization of target atoms by high-energy heavy-ion impact

Absolute cross sections for helium single and double ionization in collisions with fast, highly charged projectiles

Absolute cross sections for single and double ionization of helium have been measured for highly charged (24<or=q<or=92) and fast (3.6 MeV u-1<or=Ep<or=1 GeV u-1) heavy-ion impact. The ratios of double-to-single ionization are found to deviate drastically from the prediction of first-order theories: in the strong perturbation regime they fall below the scaling of Knudsen et al. (1984) even for 120 MeV u-1 U91+ impact, whereas a strong increase by a factor of 3 relative to this semi-empirical prediction is observed in the regime of low perturbations for 0.5 and 1 GeV u-1 Kr36+ impact.

Calculation of Incident Angle Dependence of Ion-Induced Kinetic Electron Emission from Aluminum

The Monte Carlo simulation of transport of incident ions and recoiling target atoms is combined with the semiempirical theory of ion-induced kinetic electron emission (KEE) for calculating the incident angle dependence of the KEE yields. The calculation was made for light and heavy ion impact on Al in the energy range from 100 eV to 1 MeV. The present results are consistent with the experimental data and have revealed the origin of the deviation from the inverse cosine law, which corresponds to the contributions from backscattering ions and recoiling target atoms.

Search for nuclear reactions produced by the impact of heavy molecular ions onto LiD

Preliminary evidence for light element fusions induced by the impact of heavy molecular ions, with mass around 430 a.m.u. (obtained by fragmentation of Re2(CO)10) and energy 140 keV, onto LiD target is presented. The experimental arrangement excludes the impact of fast light particles due to fragmentation inside the acceleration column and supports the idea of a «new» underlying physics.

Molecular and cluster ions produced from frozen C 2H 2 molecules under energetic, heavy ion impact

Secondary ions have been measured due to collisions of 1.25 MeV/amu Ar q+ ( q = 12 or 14) projectile ions with C 2H 2 molecular targets frozen on a thin foil which was cooled to liquid nitrogen temperature. In the present experiments, positively charged cluster ions such as [CH m (C 2) n ] + and[C 2H m (C 2) n ] + ( m = 0, 1, 2 or 3) and negatively charged cluster ions [CH m (C 2) n ] − and [C 2H m (C 2) n ] − ( m = 0 or 1) have been observed. The charge/mass spectrum of the atomic and molecular ions frozen C 2H 2 targets was also found to be quite different from that in gaseous C 2H 2 targets.

Al double core electron excitation in asymmetric collisions

We report a detailed Auger study on the double 2p electron excitation in Al by bombarding polycrystalline Al with 5–15 keV noble gas ions (Ne +, Ar +, Kr +, and Xe +) and Mg x Al 1 − x alloys ( x = 0, 0.25, 0.50, and 0.75) with Ar + ions. Fo resolved spectra show three well distinct narrow atomic L 2-Auger peaks at ~ 76, ~ 82, and ~ 85.5 eV which exhibit clear Doppler shifts. These doubly excited Al Auger lines are detectable only for heavy noble gas ion (Ar +, Kr +, and Xe +) impact along off-normal incidence directions suggesting that the excitation occurs in the primary asymmetric collisions. However, for Mg x Al 1 − x alloys such atomic L 2-Auger peaks are clearly present even for normal Ar + ion incidence, unambiguously indicating that the Al double core electron excitation may also occur in collisions with lighter partners. Based on the linear dependence of the intensity of the prominent Al L 2MM peak normalized to its surface concentration on the surface Mg concentration we suggest that it is due to transfer of double L-shell vacancies from one Mg atom excited in the primary Ar +Mg collision to an Al atom in a subsequent MgAl encounter through, for example, 4fσ-3dσ radial coupling.

Al double core electron excitation in asymmetric collisions

Abstract We report a detailed Auger study on the double 2p electron excitation in Al by bombarding polycrystalline Al with 5–15 keV noble gas ions (Ne+, Ar+, Kr+, and Xe+) and MgxAl1 − x alloys (x = 0, 0.25, 0.50, and 0.75) with Ar+ ions. Fo resolved spectra show three well distinct narrow atomic L2-Auger peaks at ~ 76, ~ 82, and ~ 85.5 eV which exhibit clear Doppler shifts. These doubly excited Al Auger lines are detectable only for heavy noble gas ion (Ar+, Kr+, and Xe+) impact along off-normal incidence directions suggesting that the excitation occurs in the primary asymmetric collisions. However, for MgxAl1 − x alloys such atomic L2-Auger peaks are clearly present even for normal Ar+ ion incidence, unambiguously indicating that the Al double core electron excitation may also occur in collisions with lighter partners. Based on the linear dependence of the intensity of the prominent Al L2MM peak normalized to its surface concentration on the surface Mg concentration we suggest that it is due to transfer of double L-shell vacancies from one Mg atom excited in the primary Ar+Mg collision to an Al atom in a subsequent MgAl encounter through, for example, 4fσ-3dσ radial coupling.

Multiply-charged ions and cluster ions produced from frozen CO2 and H2O targets in energetic, heavy ion collisions

Some frozen gases (CO2 and H2O) are used to produce multiply charged recoil ions as well as cluster ions under high energy, heavy ion impact. The ions produced in the frozen gas targets are found to be quite different from those in gas phase targets.

Cluster ions and multiply charged ions formed in frozen CO2 molecules under heavy ion impact

A variety of cluster ions, positive or negative, as well as multiply charged atomic ions have been observed from the frozen CO2 targets under (MeV/amu) energetic, highly charged projectile ion impact. Their spectra are found to be quite different from those produced in the cooled expanding CO2 gas targets.

Up Close: ANOREM, Six Laboratories Devoted to Materials Research

In Caen in northwest France near the Normandy beaches, six laboratories involved in materials research have joined together to promote the scientific process; to discuss their topics, projects and results; and, more generally, to work together in an interdisciplinary way. The six laboratories that form the Association Normande de Recherches sur les Matériaux (ANOREM, or the Normandy Association for Materials Research) are the following:■ Atomic Spectroscopy Laboratory■ Catalysis and Spectrochemistry Laboratory,■ Center for Interdisciplinary Research with Heavy Ions (CIRIL),■ Molecular Chemistry Laboratory,■ Crystallography and Materials Science Laboratory (CRISMAT), and■ Materials Science EngineeringLaboratory (LERMAT).These laboratories perform research on topics ranging from structural chemistry and radiation damage to high Tc superconductors and the European Hermes shuttle project.Among the activities of the Laboratoire de Spectroscopie Atomique, the following two belong to the field of materials science:1. Color center laser research, which spans Bridgman growth, shaping, polishing and coloring of active samples. Besides making “classical” samples, researchers are looking for new materials with improved stability against illumination and thermal bleaching. In particular, researchers are trying to master additive coloration of pure and doped NaF. (This crystal is usually colored by ionizing radiation since its coloration by additives is quite difficult.) There is a good prospect for building a flashlamp-pumped, tunable infrared laser operating at room temperature with a sample which would be “everlasting,” due to an in situ régénération of the active centers by the flashlamp itself. Studies are also being conducted on how to make alkali halide samples with multi-dielectric coatings (either anti-reflecting or mirror). Researchers are investigating such questions as: Should the coating be made before or after coloration? How does it adhere at liquid nitrogen temperatures? What precautions should be taken against attack by moisture?2. Optical spectroscopy of defects created in insulating solids by impact of high energetic heavy ions. This research is a joint project with the GRIL and is described below.

Desorption of secondary negative ions induced by impact of heavy ions near the bohr velocity

The yields of secondary negative ions from solid samples of both valine (MW = 117) and gold have been measured using Xe +, Kr + and Ar + incident ions in the energy range 400 keV—3 MeV, where the calculated nuclear and electronic stopping powers are comparable in magnitude and opposite in slope with respect to the velocity of the incident ions. Results show that the electronic stopping power plays a predominant role in the yield of valine (MH) − ions, whereas the nuclear stopping power is responsible for the yield of gold negative ions. Many low mass secondary ion species are also observed. The shapes of the yield data as a function of the primary ion velocity indicate that the desorption of C −, CH −, O −, F − and OH − ions are related to the nuclear stopping power, whereas desorption of C 2N − and CN − are related to the electronic stopping power.

Two-fragment coincidence studies of molecular coulomb explosions induced by heavy ion impact

Time-of-flight (TOF) spectroscopy was used to study the ionic species produced in collisions of 40 MeV Ar 13+ with molecular oxygen. Ions from the dissociation of molecular ions having charges as high as 10 + were observed. The flight times of the first ion and the difference in flight times between the first and second ions of binary dissociation events were recorded event-by-event, thereby retaining their correlation. Off-line sorting of the data provided TOF and time difference spectra containing well resolved peaks associated with each of the charge division pairs produced in the dissociation process.

High-resolution target Auger spectroscopy at the impact of energetic heavy ions on Ne

The main results and conclusions of a long series of measurements on Ne K Auger spectra produced by the impact of different high-velocity (14.9 a.u.) ions are given.

Resonant multielectron transfer in solid oxides following double K-shell ionization by heavy-ion impact.

The K\ensuremath{\alpha} hypersatellite spectra of oxygen, obtained by bombardment of various solid oxides with 2-MeV/amu beams of C and Ar ions, were measured using a curved-crystal spectrometer. In the spectra for the compounds CaO, SrO, ${\mathrm{CeO}}_{2}$, and three of the oxides of Ti, some of the hypersatellite peaks appeared to be enhanced while others were suppressed. These features are indicative of resonant electron transfer processes caused by the energy matching of valence levels in the multiply ionized oxygen ion with those of its neighboring metal ions. In all cases except CaO, the spectra suggest that correlated multielectron transfer is involved, in which as many as four electrons are exchanged between the two ions. A method developed previously for estimating the energy change associated with the electron exchange was generalized to cover multielectron transfer, and corrections for extra-atomic relaxation were included. Calculations employing this method strongly support the resonant multielectron transfer hypothesis.