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Most sputtering yield measurements for solid N 2 are reported for stopping powers lower than 10 − 13 eV cm 2 /molecule. We measured the sputtering yield for solid N 2 at stopping powers, in the electronic regime, above 10 − 12 eV cm 2 /molecule, extending the range of such measurements by more than an order of magnitude, using a 33 MeV 58Ni 9 + swift heavy ions beam. The evolution of the thin N 2 ice films was monitored in-situ by mid-infrared spectroscopy (FTIR) during irradiation. As N 2 is only weakly infrared active, and can be hardly monitored directly via an infrared absorption mode in such experiments, we use the Fabry–Perot interference fringes of the ice film to evaluate, via an optical model, the erosion of the N 2 film as a function of ion fluence. A sputtering model including several sputtering crater shapes is developed and tested against experimental data. We derive the sputtering yield for a semi-infinite N 2 ice film and its dependence with the ice thickness for thin film conditions, monitoring the N 2 ice sputtering depth. We combine the results with previous measurements at lower stopping powers to derive the electronic sputtering of solid N 2 over a large stopping power range.

A typographical error remains in the publication of the first name of Aymann S. El-Said: Aymann should be written as Ayman.

International audience; Sputtering experiments were performed by irradiating LiF, NaCl, and RbCl crystals with various swift heavy ions like S, Ni, I, Au with energies between 60 and 210 MeV, C$_{60}$ clusters between 12 and 30 MeV or Pb ions between 730 and 6040 MeV. Sputtered species are collected on arc-shaped catchers and subsequently analyzed by elastic recoil detection analysis or Rutherford backscattering analysis. The study focuses on angular distributions and total yields for LiF and covers a broad range of experimental parameters including cleaved or rough sample surfaces, ion fluence, beam incident angles, and different ion velocities leading to electronic energy loss (S$_{e}$) values from 5 to 45 keV/nm. In most cases, the angular distribution has two components, a jet-like peak perpendicular to the surface sample superimposed on a broad isotropic cosine distribution whatever is the beam incident angle. The observation of the jet depends mainly on the surface flatness and angle of ion incidence. However, the jet does not appear clearly when irradiated with C$_{60}$ cluster. The sputtering yield is stoichiometric and characterized by huge total yields of up to a few 10$^{5}$ atoms per incident ion. The yield follows a power law as function of electronic energy loss, Y follows an exponential law with S$_{e}^{n}$ with n ~ 4. While the azimuthal symmetry for sputtering is observed at low ion velocity (~1 MeV/u), it seems to be lost at high velocity (>4 MeV/u). The data provide a comprehensive overview how the angular distribution and the total sputtering yield scale with the energy loss, beam incidence angle and ion velocity. Complementary experiments have been done with NaCl and RbCl targets confirming the observation made for LiF.[graphic not available: see fulltext][graphic not available: see fulltext]

International audience; Sputtering experiments with swift heavy ions in the electronic energy loss regime were performed by using the catcher technique in combination with elastic recoil detection analysis. The angular distribution of particles sputtered from the surface of LiF single crystals is composed of a jet-like peak superimposed on a broad isotropic distribution. By using incident ions of fixed energy but different charges states, the influence of the electronic energy loss on both components is probed. We find indications that isotropic sputtering originates from near-surface layers, whereas the jet component may be affected by contributions from depth up to about 150 nm.

International audience; This work presents a physicochemical study of frozen amorphous methane (at 16 K) under bombardment by medium-mass ions (15.7 MeV 16O5+) with implications for icy bodies in the outer Solar System exposed to the action of cosmic rays and energetic particles. The experiment was performed at the Grand Accélérateur National d'Ions Lourds (GANIL) located in Caen, France. The results demonstrate that irradiation of CH4-containing ices by swift medium mass ions with delivered energy covering both stopping power regimes until its implantation on ice (i.e. electronic and nuclear) leads to the production of many hydrocarbons, such as C2H2, C2H4, C2H6, and C3H8 (the most abundant daughter species produced). Values for the effective dissociation cross section of CH4 and the average value for the effective formation cross-sections of its daughter species were about 10−14 cm2 and 10−15 cm2, respectively. The half-life of methane ice in the presence of swift medium mass ions extrapolated to some outer Solar System environments is estimated to be around 106 years. The measured sputtering yield of methane due to incoming swift ions was about 7.30 × 105 molecules per impact. Such parameters can be used as models to estimate the amount of CH4 and other molecular species desorbed from the icy surfaces that are constantly being incorporated to the gaseous atmosphere in the vicinity of these outer Solar System bodies due to the presence of energetic particles and cosmic rays.

Silicates are the dominant surface material of many Solar System objects, which are exposed to ion bombardment by solar wind ions and cosmic rays. Induced physico-chemical processes include sputtering which can contribute to the formation of an exosphere. We have measured sputtering yields and velocity spectra of secondary ions ejected from nepheline, an aluminosilicate thought to be a good analogue for Mercury's surface, as a laboratory approach to understand the evolution of silicate surfaces and the presence of Na and K vapor in the exosphere. Experiments were performed with highly charged ion beams (keV/u–MeV/u) delivered by GANIL using an imaging XY-TOF-SIMS device under UHV conditions. The fluence dependence of sputtering yields gives information about the evolution of surface stoichiometry during irradiation. From the energy distributions N(E) of sputtered particles, the fraction of particles which could escape from the gravitational field of Mercury, and of those falling back and possibly contributing to populate the exosphere can be roughly estimated.

Sulfuric acid has been suggested to be present on the surface of the jovian moon Europa where it is mixed with the dominant water ice. The formation mechanism of sulfuric acid is still under discussion. We present new experimental results on the implantation of S q + ( q = 7, 9, 11) ions at an energy range between 35 and 176 keV in water ice at 80 K. Previous results on 200 keV S + implantation in H 2 O at 80 K have also been included in the data analysis. Experiments with multiply-charged ions at different energies are particularly relevant to simulate the complexity of the irradiation environment to which the surface of Europa is exposed being embedded in the jovian magnetosphere. The experiments were performed at the low energy ion beam facility ARIBE of GANIL in Caen (France). 35–176 keV S q + ( q = 7, 9, 11) ions were implanted in solid H 2 O layers which were frozen at 80 K. Fourier Transform Infrared Spectrometry (FTIR) was used to analyze the sample in the 5000–600 cm −1 (2–16.7 μm) region with a spectral resolution of 1 cm −1 . The results of our experiments indicate that implantation produces hydrated sulfuric acid with yields that increase with ion energy, from 0.12 molecules ion −1 for 35 keV ions to 0.64 molecules ion −1 for 200 keV ions. We have also searched for the production of SO 2 and H 2 S, but we were not able to find any evidence for their synthesis. We conclude that sulfur ion implantation is the dominant formation mechanism of hydrated sulfuric acid at Europa. The suggestion that the observed distribution of sulfuric acid on the surface is well correlated with the local flux of sulfur ions find a full explanation by present experimental data.

Methane (CH4) ice is found in the interstellar medium and in several bodies of the Solar system, where it is commonly exposed to cosmic rays and stellar winds. The chemical, physical and structural effects induced by fast heavy ions in thin layers of pure CH4 ices at 15 K are analysed by mid-infrared spectroscopy (Fourier transform infrared). Different pure CH4 ice samples were irradiated with 6 MeV 16 O 2 + , 220 MeV 16 O 7 + , 267 MeV 56 Fe 22 + and 606 MeV 70 Zn 26 + ions at Grand Acc´´ National d’Ions Lourds/France. Results show that CnHm molecules, where n = 2–4 and m = 2(n − 1) to 2(n + 1) and radical species CH3 ,C 2H3 and C2H5 are formed. The destruction cross-sections of CH4 ice and the formation cross-sections of new molecules CnHm are reported. The extrapolation of current results allow us to estimate the half lives of CH4 ices in the interstellar medium and the Solar system (Earth orbit) as about 600 × 10 6 and 600 yr, respectively. This huge ratio strongly suggests that the vast majority of

We present new experimental results relative to 144 keV S 9 + or Ar 9 + ion implantation in targets made of oxygen rich frozen gases (O2, CO2) and mixtures with water ice. Spectra in the UV (200–400 nm) range have been obtained before and after implantation. The targets have been selected because they can be representative of the parent molecules from which SO2 and O3, observed to be present on the surfaces of Jupiter’s icy Moons, could be formed due to radiolysis induced by the abundant magnetospheric ions. The results indicate that sulfur dioxide is not detectable after sulfur implantation in oxygen bearing species. Ozone is formed after argon and sulfur ion implantation. Sulfur implantation in O2 and CO2 targets also induces the formation of a band centered at about 255 nm (that we tentatively attribute to SO3 − radicals). In the mixtures with water the band appears initially at the same wavelength and shifts to about 247 nm at higher ion fluences possibly indicating the formation of sulfite (HSO3 − ) ions. An absorption band observed on Ganymede is well fitted by using three components: ozone, sulfite ions and a not identified component having an absorption band centered at 298 nm. In all of the studied cases ion implantation produces a spectral reddening over the investigated spectral range (200–400 nm) that well mimics the observed spectral slopes of Jupiter’s icy satellites.

Conducting ion tracks in tetrahedral amorphous carbon (ta-C) thin films were generated by irradiation with swift heavy ions of well-defined charge state. The conductivity of tracks and the surface topography of the films, showing characteristic hillocks at each track position, were investigated using conductive atomic force microscopy measurements. The dependence of track conductivity and hillock size on the charge state of the ions was studied using 4.6 MeV/u Pb ions of charge state 53+, 56+ and 60+ provided by GANIL, as well as 4.8 MeV/u Bi and Au ions of charge state from 50+ to 61+ and 4.2 MeV/u 238U ions in equilibrium charge state provided by UNILAC of GSI. For the charge state selection at GSI, an additional stripper-foil system was installed at the M-branch that now allows routine irradiations with ions of selected charge states. The conductivity of tracks in ta-C increases significantly when the charge state increases from 51+ to 60+. However, the conductivity of individual tracks on the same sample still shows large variations, indicating that tracks formed in ta-C are either inhomogeneous or the conductivity is limited by the interface between ion track and Si substrate.

The chemical and physical effects induced by fast heavy ion irradiation on frozen pure methanol (CH3OH) at 15 K were studied. These energetic ions can simulate the energy transfer processes that occur by cosmic ray irradiation of interstellar ices, comets and icy Solar system bodies. The analysis was made by infrared spectroscopy (Fourier transform infrared) before and after irradiation, with 16-MeV 16O5+, 220-MeV 16O7+, 606-MeV 65Zn20+ and 774-MeV 86Kr31+ ion beams. Integrated values of the absorbance of the main methanol bands were determined. The induced CH3OH dissociation gives rise to the formation of molecular species, particularly H2CO, CH2OH, CH4, CO, CO2, HCO and HCOOCH3. Their formation and dissociation cross-sections were determined. H2CO and CH4 molecules are in general the most abundant new products of the four beams analysed. Except for the HCO and CH2OH species, cross-sections increased with the electronic stopping power, roughly as σ∼S3/2e. The G values for CH3OH destruction by fast heavy ion irradiation with Zn and Kr beams were found to be considerably larger than those for oxygen, helium or hydrogen. As an astrophysical implication, the S3/2e power law should be very helpful for predicting the CH3OH formation and dissociation cross-sections for other ion beam projectiles and energies. As astrophysical point of view, the analysis of the predictions reveals the unexpected importance of iron and some other heavy ion constituents of cosmic rays in astrochemistry.

Ion cluster desorption yields from LiF were measured at PUC-Rio with ≈0.1 MeV/u N q+ (q = 2,4,5,6) ion beams by means of a time-of-fight (TOF) mass spectrometer. A 252Cf source mounted in the irradiation chamber allows immediate comparison of cluster emissions induced by ≈65 MeV fission fragments (FF). Emission of (LiF) n Li+ clusters are observed for both the N beams and the 252Cf fission fragments. The observed cluster size n varies from 1 to 6 for N q+ projectiles and from 1 to ≈40 for the 252Cf-FF. The size dependence of the Y(n) distributions suggests two cluster formation regimes: (i) recombination process in the outgoing gas phase after impact and (ii) emission of pre-formed clusters from the periphery of the impact site. The corresponding distribution of ejected negative cluster ions (LiF) n F− closely resembles that of the positive secondary (LiF) n Li+ ions. The desorption yields of positive ions scale as Y(n) ∼ q 5. A calculation with the CASP code shows that this corresponds to a cubic scaling ∼S 3 with the electronic stopping power S e , as predicted by collective shock wave models for sputtering and models involving multiple excitons (Frenkel pair sputtering). We discuss possible interpretations of the functional dependence of the evolution of the cluster emission yield Y(n) with cluster size n, fitted by a number of statistical distributions.

Water, carbon oxide, carbon dioxide, and ammonia ices are known to be pervasive constituents of the solar system and the interstellar medium. These ices and ice-covered surfaces are exposed to bombardment by energetic projectiles like photons, electrons, and ions. Laboratory experiments have been carried out to study the effects of such irradiation. However, there is a clear lack of information about the interaction of heavy ion components of solar/stellar wind and galactic cosmic rays (e.g. Fe) with ices in the keV to GeV energy range. The objective of this work is to study the effects produced in astrophysical ices by highly charged nickel ions at relatively high energy (∼50–500 MeV) in the electronic energy loss regime, and to compare them with those produced by protons, photons, and electrons. Our results for CO 2 and CO indicate that sputtering induced by heavy ions can be an important mechanism to desorb molecules in astrophysical environments.

Storage rings as the ESR and the future NESR in the FAIR project are unique tools to study the dynamics of electron-ion and ion-atom collisions in the realm of strong perturbations and short interaction times. A telling sign of the character of such collisions are the electrons emitted into the continuum. For high Z projectiles and low Z targets the projectile centred continuum is dominating. Precision studies of these electrons emitted in relativistic collisions thus are of paramount importance for an understanding of the ionization mechanisms active in transferring electrons into the continua. Forward electron spectroscopy thus appears to be the tool of choice. For high precision studies in collision spectroscopy of high Z projectiles we have implemented an imaging forward electron spectrometer into the ESR supersonic jet target zone. In combination with a reaction microscope to be implemented next this enables investigations of several fundamental processes ranging from kinematically complete studies of multiple ionization and (e, 2e) on ions to radiative and non-radiative electron transfer processes to the projectile continuum and for the first time kinematically complete measurements of the short-wavelength limit of the electron nucleus Bremsstrahlung. We report first results.

Swift heavy-ion induced effects in condensed matter have important applications in, for example, materials science (materials under irradiation as in present or future nuclear power plants, nano-structuring of materials and their surfaces), radiation chemistry (radiolysis), and radiation medicine (tumor therapy with ions human exposure to cosmic rays). We refer the readers to Ref. [1] for a recent book on the fundamentals and applications of ion beams. At high projectile energies, collisions between the ions and the target electrons are the dominant processes of energy loss of the projectiles. The primary electrons and their subsequent secondary interactions lead to the deposition of energy around the ion trajectory.

A rather complete experimental study of forward and backward electron velocity spectra from thin foils bombarded with ions at constant velocity of 30 atomic units (23MeV u^-1) was performed. Three different beams ( 12C3+ , 58Ni14+ and 197Au36+ and six different targets ( 12C , 27Al , natNi , natAg , 197Au and 209Bi of approximately 90μg cm^-2 thickness were used. This procedure allowed to study the evolution of electron emission (velocity and angular distributions) for the [projectile; target] matrix [ C , Ni , Au ; C , Al , Ni , Ag , Au , Bi ] in a wide angular range. The projectile and target dependence of absolute cross-sections for binary encounter-, Auger- and backward-emitted electrons are analyzed.

Measurements of the secondary electron yields from uranium dioxide under impact of Xeq+ (q = 10–25, 0.03 keV ⩽ EKin ⩽ 81 keV) ions are presented. A strong increase of the secondary electron yield is observed with increasing charge state of the projectile both at normal and oblique incidences. No variation of the electron yield with the projectile kinetic energy is observed at normal incidence. Therefore, the electron emission process in highly charged ion – uranium dioxide (UO2) interactions is dominated by potential electron emission.

Insulating (MYLAR), semi-insulating (MYLAR-Au) and conducting foils have been bombarded by very energetic 64 MeV u−1 78Kr32+ ions. The velocity spectra of fast electrons emitted in the backward and forward directions have been measured and analyzed as a function of the elapsed time in the run. A shift of binary encounter and convoy electrons emitted in the forward direction toward lower velocities has been observed with insulating targets. No such shift occurs with metallic targets. The surface potential evolves with time (i.e. ion fluence) both at forward and backward emission angle. It is shown that strong bulk charging of insulating targets leads to a positive potential as high as 9 kV before charge breakdown.

First results on swift heavy ion induced electron emission from solids obtained with a reaction microscope are presented. This advanced technique, which is successfully used since quite some time to study electron ejection in ion–atom collisions, combines the measurement of the time-of-flight of electrons with imaging techniques. A combination of electric and magnetic fields guides the ejected electrons onto a position sensitive detector, which is capable to accept multiple hits. From position and time-of-flight measurement the full differential emission characteristics of up to 10 electrons per single incoming ion can be extracted. As a first example, we show energy spectra, angular distributions and the multiplicity distribution of electrons from impact of Au24+ (11 MeV/u) on a thin carbon foil (28 μg/cm2).

The accelerator facilities of GANIL allow studying ion–surface collisions in a wide range of projectile velocities. On the one hand, high velocity heavy ions (MeV/ u ) where the electronic energy loss is dominant (electronic sputtering), and on the other hand, low velocity highly charged ions (keV/ q ) are available. In the latter case, nuclear stopping (elastic collision cascades) is more important. Possibly, further effects related to the high projectile charge and corresponding high potential energy can occur (potential sputtering). We use a combination of imaging techniques ( XY ) and time-of-flight (TOF) spectroscopy to measure the complete velocity vector of emitted secondary ions. We present results on energy and angular distributions of 7 Li + (atomic ions) sputtered from a LiF crystal by Ca 17+ (9 MeV/ u ) and Xe 21+ (17 keV/ q = 350 keV) ions. The energy distributions differ strongly thus clearly showing that the material responds differently to energy deposition by purely electronic stopping (high velocity projectiles) and slow highly charged ions. We also compare the angular distributions of emitted Li + ions and neutrals in the electronic stopping regime.

Highly energetic projectiles (20 MeV/u E beam v beam (the ion beam velocity) and 2 v beam . Results obtained both at the Catania LNS superconducting cyclotron CS with 58 Ni 14+,19+ (23 and 45 MeV/u) and at Ganil with 78 Kr 32+,34+ (64 MeV/u) are presented. Absolute emission cross-sections and kinematic properties are discussed.

Solid carbon dioxide (CO2) is found in several bodies of the solar system, the interstellar medium (ISM) and young stellar objects, where it is exposed to cosmic and stellar wind radiation. Here, the chemical and physical modifications induced by heavy ion irradiation of pure solid CO2 at low temperature (T = 15–30 K) are analyzed. The experiments were performed with Ti (550 MeV) and Xe (630 MeV) ions at the UNILAC of GSI/Darmstadt and with Ni ions (46 and 52 MeV) at IRRSUD of GANIL/Caen. The evolution of the thin CO2 ice films (deposited on a CsI window) was monitored by mid-infrared absorption spectroscopy (FTIR). The dissociation rate of CO2, determined from the fluence dependence of the IR absorption peak intensity, is found to be proportional to the electronic stopping power Se. We also confirm that the sputtering yield shows a quadric increase with electronic stopping power. Furthermore, the production rates of daughter molecules such as CO, CO3 and O3 were found to be linear in Se.

The collision system U88+ + N2 at a low-relativistic projectile energy of 90 MeV/u has been analyzed experimentally and theoretically with respect to fast electrons emitted with a velocity ve close to the projectile velocity, vp ≈ ve, at an observation angle of e ≈ 0°, i.e., in the direction of the projectile beam. Three distinct processes are identified, where each of the underlying charge-transfer mechanisms leads to a characteristic feature in the asymmetry of the observed electron energy distribution. The experimental results for each of the three processes are compared to the corresponding theoretical models.

International audience; Over more than a decade, experimental studies of the production and transport of projectile excited states in thin solid targets have been performed at GANIL for Ar17+ and Kr35+ in the so-called high velocity domain. A range of target thicknesses from single collision condition to equilibrium has been investigated. X-ray spectroscopy techniques have allowed us to determine absolute nℓ populations of core and Rydberg projectile states, as well as the relative population of fine structure substates (nℓj). In parallel, theoretical simulations to treat on the same footing all the competing processes, i.e., collisions, radiative decay and dynamical screening due to the wake field, have been developed. Methods based on either master equations or Monte Carlo approaches have allowed us to reach an unprecedented precision in the description of the ion transport in matter in the perturbative regime. In particular, a first direct measurement of the wake field usually extracted from ion stopping power has been performed.

Expérience GANIL/IRSSUD/SME/LISE; International audience; Under cosmic irradiation, the interstellar water ice mantles evolve towards a compact amorphous state. Crystalline ice amorphisationwas previously monitored mainly in the keV to hundreds of keV ion energies.Aims. We experimentally investigate heavy ion irradiation amorphisation of crystalline ice, at high energies closer to true cosmic rays,and explore the water-ice sputtering yield.Methods. We irradiated thin crystalline ice films with MeV to GeV swift ion beams, produced at the GANIL accelerator. The iceinfrared spectral evolution as a function of fluence is monitored with in-situ infrared spectroscopy (induced amorphisation of theinitial crystalline state into a compact amorphous phase).Results. The crystalline ice amorphisation cross-section is measured in the high electronic stopping-power range for different temperatures.At large fluence, the ice sputtering is measured on the infrared spectra, and the fitted sputtering-yield dependence, combinedwith previous measurements, is quadratic over three decades of electronic stopping power.Conclusions. The final state of cosmic ray irradiation for porous amorphous and crystalline ice, as monitored by infrared spectroscopy,is the same, but with a large difference in cross-section, hence in time scale in an astrophysical context. The cosmic ray water-icesputtering rates compete with the UV photodesorption yields reported in the literature. The prevalence of direct cosmic ray sputteringover cosmic-ray induced photons photodesorption may be particularly true for ices strongly bonded to the ice mantles surfaces, suchas hydrogen-bonded ice structures or more generally the so-called polar ices.

Porous water ice and water ice mixtures H 2 O:X (X = CO, CO 2 and CH 4 ) produced at 15 K, with film thicknesses in the 0.5–1 μm range, were irradiated by swift ions and monitored by mid-infrared spectroscopy (FTIR). The analysis of the evolution of the pure water ice infrared absorption on ion beam dose reveals a strong correlation among three quantities: (i) the absorbance of the most intense band (3250 cm −1 ), (ii) the wavelength of the maximum absorbance of this band and (iii) the absorbance of the OH-dangling bonds. This correlation is interpreted as indications of the water ice compaction by irradiation: as the beam fluence increases, the ice porosity decreases, the dangling bond peaks collapse and the area and position of the 3250 cm −1 band vary exponentially, all of them evolving with the same compaction cross section ( σ c ). The linear dependence σ c ∝ S e ( S e being the electronic stopping power) is observed for both pure and mixed water ices, confirming previous results. We suggests that the infrared absorption A -value varies with dose as ( 1 - ζ e - D / D 0 ) during the compaction process ( D 0 = 0.2 eV/molec being the effective energy density to eliminate the OH-db, and ζ is a parameter characterizing the porosity). These findings may be used as a diagnostic tool to probe the morphology of water ices occurring in the outer Solar System and in the ISM.

For the collision system ${\text{U}}^{88+}+{\text{N}}_{2}$ at a collision energy of 90 MeV/u, the energy distribution of electrons being nonradiatively captured from the target into the projectile continuum has been measured under an angle of ${0}^{\ensuremath{\circ}}$ with respect to the projectile beam axis. This measurement of the electron-capture-to-continuum cusp with the highest effective projectile charge ${Z}_{p}^{\mathrm{eff}}=88$ at a near-relativistic collision velocity of $\ensuremath{\beta}\ensuremath{\approx}0.41$ is shown to be characterized by a strong asymmetry in the cusp shape. By comparing the data to measurements of the radiative-electron-capture-to-continuum cusp for the same collision system, the opposite asymmetry of the cusp is traced back to the varying underlying mechanisms. The experimental results are compared with the two theoretical calculations available for this process, one of them in the semirelativistic impulse approximation and the other in the nonrelativistic continuum-distorted-wave approach. A corresponding fully relativistic treatment may be motivated by the presented experimental data.

CAS; International audience; In 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.

In nuclear and atomic experiments at high incident ion energies, 20 MeV/ u E u , the impact of swift heavy ions on thin solid targets is a source of fast electrons. The knowledge of their spatial and kinematical distributions is very useful for experimental nuclear and radiobiological applications as well as testing atomic ionization theories. An overview on the main mechanisms underlying the production of the electrons is given. Some recent results obtained at the Catania LNS superconducting cyclotron, mainly with a 45 MeV/ u 58 Ni 19+ beam are shown. In particular, the production and the properties of binary encounter-, convoy-, in-flight Auger- and backward emitted electrons are discussed.

The forward and backward electron emission yields γ F and γ B have been calculated by Monte Carlo simulation for protons (H + ) and hydrogen atoms (H 0 ) (with energies between 25 keV and 5 MeV) incident on thin amorphous carbon foils. Direct electron excitations by the incident projectiles as well as electron excitations resulting from charge exchange processes undergone by H + or H 0 have been taken into account. For the latter, Auger and Shell processes have been considered. Subsequent electron transport has been considered in order to calculate the forward and backward electron emission yields γ F and γ B .

The forward ( γ F ) and backward ( γ B ) electron emission yields have been measured for protons incident on thin carbon foils for incident energies between 2 and 7 MeV as a function of the target thickness. Comparisons with theoretical results obtained by Monte Carlo simulations are presented. In particular, the Meckbach factor R γ = γ F / γ B is discussed.

The “Fermi shuttle” acceleration of electrons in ion–atom collisions, i.e. multiple collision sequences of electrons bouncing off the projectile and target nuclei, can lead to the emission of very energetic electrons (i.e. with velocities higher than the binary encounter electrons). We performed measurements of the evolution of the Fermi shuttle electron yield with the induced perturbation and the target atomic number. The yield increases with the perturbation parameter (ratio of projectile charge and projectile velocity q/vP), which was varied from q/vP ≈ 0.2 (weak perturbation) to q/vP ≈ 2 (strong perturbation). We also introduce a more realistic scaling parameter, which accounts for the re-bouncing of the electrons on target and projectile, and show that the yields increase as a function of this parameter. For a given projectile, the Fermi shuttle electron yield increases with the target atomic number. Furthermore, we show that the velocity distribution of the high-energy electrons is exponentially decreasing N(v) ∼ exp(−nv) and exhibits the same evolution of the slope n with projectile velocity as in the case of Fermi accelerated deuterons.

Measurements of the cluster size (n) distribution of secondary (UOx)+n ions from sputtering of uranium dioxide (UO2) by Ne8+, Ar8+ and Xeq+ ions (q=10, 23) at fixed kinetic energy (81 keV) have been performed with a time-of-flight mass spectrometer. The cluster ion yields Y follow a power law Y(n)∼nδ with -2.1

The detailed knowledge of the structure of ion tracks is a key issue for our understanding of radiation effects in condensed matter. Important examples are the radial energy deposition profile by electronic excitation for numerical simulations of track formation (via “Coulomb explosion” or “thermal spike”) in inert matter, and calculations of the RBE (relative biological effectiveness) of heavy particles in living matter (with important applications in dosimetry and hadrontherapy). In both cases, differential electron ejection cross sections are used as input parameter. The precursor of track formation is thus electron ejection from target atoms, or from the projectile itself. These primary electrons and their subsequent secondary interactions lead to the deposition of energy along and around the ion trajectory. We first briefly discuss “primary ionization” (binary encounter and soft electron emission, multiple collision sequences: “Fermi shuttle”) common to single atoms (gas targets) and condensed matter. Then, specific effects in condensed matter (electron transport, jet-like electron spikes, wake effects due to collective excitation of plasmons and emission of shock wave electrons) will be presented. Finally, we concentrate on effects connected to the high density of deposited energy and strong perturbation induced by heavy particles such as heavy ions and clusters (reduction effects due to screening, transport and “sweeping away”, multiple ionization, electronic temperatures from Auger spectroscopy).

Doubly differential electron velocity spectra induced by 36Ar18 + (95 MeV/u) from thin target foils (C, Ni, Ag, Au) were measured at GANIL (Caen, France) by means of the ARGOS multidetector and the time-of-flight technique. The main features observed in the forward spectra are convoy electrons, binary-encounter electrons, and (for the Au target only) a high-velocity tail which we attribute to a “Fermi shuttle” acceleration mechanism. Backward spectra do not show distinct structures. The spectra allow us to determine absolute singly differential cross-sections as a function of the target material and the emission angle. The convoy electron yield increases with the target atomic number, but for C their yield is so small that our experiment is not able to detect them. Absolute doubly differential cross-sections for binary-encounter electron ejection from C targets are well described by a transport theory which is based on the relativistic electron impact approximation (EIA) for electron production and which accounts for angular deflection, energy loss and energy straggling of the transmitted electrons.

Secondary ion emission yields from polycrystalline LiF and deuterated amorphous carbon a-C:D, bombarded by isotachic projectiles at 1.4 MeV/u, were studied as a function of the projectile atomic number (C, N, Ar, Kr, Sn) and consequently, as a function of the electronic stopping power. The emitted, positively charged secondary ions were analysed by a time of flight mass spectrometer. The H + ions originate on the top surface near the track core, while heavier secondary ions (e.g. hydrocarbons) originate from the region of the track halo. Emission of Li + from LiF was observed for all projectiles. On the other hand, only Sn projectiles were able to produce D + emission from a-C:D. The results are discussed considering the deposited energy density.

In order to study the emission of energetic electrons induced by the impact of swift heavy ions on thin solid targets, we carried out a series of experiments at the superconducting cyclotron of the Catania Laboratori Nazionali del Sud. We report results on a recent experiment where electron–electron coincidences were measured in a forward ring by bombarding a thin carbon target of 7.4 μg/cm2 with 19+ 45 A MeV 58Ni beam. The velocity1–velocity2 bidimensional plot is dominated by events in which the two detected electrons have a velocity close to the beam velocity 9.03 cm/ns (convoy electrons). The remaining small fraction of coincidences has still a convoy electron and a second electron having either a velocity almost twice the beam velocity 16.5 cm/ns (binary encounter, BE electrons) or a velocity of about 12.7 cm/ns intermediate between BE and convoy velocities (IV electrons). We interprete this last intermediate component as due to in-flight de-excitation of highly excited n+58Ni ions by Auger electrons. Although less distinct, we observe also an intense peak close to the convoy velocity peak, centered at ≈9.7 cm/ns, corresponding to electrons emitted with an energy of only about ≈170 eV in the projectile rest frame of reference.

Desorption of nitrogen adsorbates from amorphous carbon (a-C) surfaces due to swift ion ( Z =6–73, q =6–54, energy 6–13 MeV/u) and electron impact (5 keV) was studied by secondary electron emission (SEE) measurements. The fluence dependence of ion induced electron emission obeys an exponential decay law as the coverage rate is in the sub-mono-layer range. The desorption yield σ varies approximately as σ ∼(d E /d x ) 3/2 or σ ∼ q 3 as a function of the electronic energy loss d E /d x and the projectile charge q , respectively. We discuss the possible desorption mechanisms connected to electronic excitation. Furthermore, we present an ESCA investigation on the mechanism for the influence of nitrogen adsorbates on SEE yields. The mechanism for the SEE enhancement effect is connected to the surface termination: nitrogen adsorbates are believed to provide surface states which generate a downwards energy band bending, which on relative scale pushes up the Fermi level towards the conduction band minimum, reducing the work function.

Secondary Electron Emission (SEE) yield measurements have been used to investigate the desorption of nitrogen adsorbates from amorphous carbon (a-C) surfaces due to swift heavy ion impact. The fluence dependence of ion induced electron emission obeys an exponential decay law when the coverage rate is in the sub-mono-layer range. This reveals the relative contribution of the both emitting zones, the “clean” one (having the SEE properties of carbon) and the covered one (with a higher SEE coefficient) to the total measured yield. The mechanism for the SEE enhancement effect is connected to the surface termination. Nitrogen adsorbates are believed to provide surface states which generate a downwards energy band bending, which on relative scale pushes up the Fermi level towards the conduction band minimum, reducing the work function and increasing the SEE yield subsequently. A shoulder observed on the rising edge of the peak of the true SE peak is ascribe to the fraction of hydrogenated termination of a-C which exhibits a lower electron affinity.

Numerical simulations of ion induced electron emission from solids mostly use the first order Born approximation within the dielectric formalism to describe valence electron excitation. As a result, the yield of emitted electrons is found to scale with the square of the projectile charge QP in contrast to experimental findings obtained with carbon targets [1]. Since similar deviations from QP2 scaling were observed for the electronic stopping power, at least a part of this deviation must be related to primary ion-electron interaction, for which an alternative description needs to be developed. We thus present here a distorted wave approach for the modelling of primary interaction, which can be expected to give better results in view of its success in describing ion-atom collisions at large impact velocity. Keeping the same description of the electron transport through the target, we show that both the electron yield and the stopping power ratios (with respect to the same quantities for C6+), as a function of the projectile charge, are better reproduced by this alternative approach. We show that low energy electron excitation is responsible for the deviation from the QP2 scaling. We also analyse the effect of the transport on the primary electrons. This distorted wave approach successfully explains the shape of the ratio of energy differential spectra for two different QP obtained in earlier experiment for Al and C. Furthermore, we predict a different behaviour of the forward and backward electron emission with respect to QP in qualitative agreement with experimental results.

International audience

The radiative electron capture of a target electron into the projectile continuum has been studied for the collision system ${\text{U}}^{88+}+{\text{N}}_{2}\ensuremath{\rightarrow}{\text{U}}^{88+}+{[{\text{N}}_{2}^{+}]}^{*}+{e}^{\ensuremath{-}}+\ensuremath{\gamma}$ at 90 MeV/$\mathrm{u}$. Using a magnetic electron spectrometer, the energy distribution of cusp electrons emitted under an angle of ${0}^{\ensuremath{\circ}}$ with respect to the projectile beam and with a velocity close to the projectile velocity has been measured in coincidence with the emitted photons under various observation angles. The experimental results provide a stringent test for the corresponding process in inverse kinematics, namely, the theory of electron-nucleus bremsstrahlung at the high-energy endpoint. For comparison this process is calculated using fully relativistic Dirac wave functions and using semirelativistic Sommerfeld-Maue wave functions.

Electronic sputtering of lithium fluoride by swift heavy ions was studied as a function of electronic energy loss (dE/dx) e . The single crystal targets were irradiated with swift heavy ion beams (166Z P 692; 46E P /M P (MeV/u) 611). This allowed varying the deposited energy by a factor of 20 (1.86dE/dx (keV/nm) 632). The sputtered secondary ions were measured from well controlled LiF targets without surface contaminations, by means of the time-of-flight technique (TOF-SIMS). The mass spectrum reveals an important contribution of clusters (over single ions), which increases with (dE/dx) e . Another observation for the strongest perturbation at high dE/dx (>8 keV/nm) is that the secondary ion yields saturate: Y(dE/dx) = constant. In contrast, at lower dE/dx (

In this work, we studied the stability of the glycine molecule in the crystalline zwitterion form, known as {\alpha}-glycine ($^{+}$NH$_{3}$CH$_{2}$COO$^{-}$) under action of heavy cosmic ray analogs. The experiments were conducted in a high vacuum chamber at heavy ions accelerator GANIL, in Caen, France. The samples were bombarded at two temperatures (14 K and 300 K) by $^{58}$Ni$^{11+}$ ions of 46 MeV until the final fluence of $10^{13}$ ions cm$^{-2}$. The chemical evolution of the sample was evaluated in-situ using Fourrier Transformed Infrared (FTIR) spectrometer. The bombardment at 14 K produced several daughter species such as OCN$^-$, CO, CO$_2$, and CN$^-$. The results also suggest the appearing of peptide bonds during irradiation but this must be confirmed by further experiments. The halflives of glycine in Interstellar Medium were estimated to be 7.8 $\times 10^3$ years (300 K) and 2.8 $\times 10^3$ years (14 K). In the Solar System the values were 8.4 $\times 10^2$ years (300 K) and 3.6 $\times 10^3$ years (14 K). It is believed that glycine could be present in space environments that suffered aqueous changes such as the interior of comets, meteorites and planetesimals. This molecule is present in proteins of all alive beings. So, studying its stability in these environments provides further understanding about the role of this specie in the prebiotic chemistry on Earth., Comment: 28 pages, 12 figures, 9 tables. Accepted to be published at Monthly Notices of the Royal Astronomical Society (MNRAS)

Formic acid (HCOOH) has been extensively detected in space environments, including interstellar medium (gas and grains), comets and meteorites. Such environments are often subjected to the action of ionizing agents, which may cause changes in the molecular structure, thus leading to formation of new species. Formic acid is a possible precursor of pre-biotic species, such as Glycine (NH2CH2COOH). This work investigates experimentally the physicochemical effects resulting from interaction of heavy and energetic cosmic ray analogues (46MeV 58Ni11+) in H2O:HCOOH (1:1) ice, at 15 K, in ultrahigh vacuum regime, using Fourier transform infrared spectrometry in the mid-infrared region (4000-600 cm-1 or 2.5-12.5 microns). After the bombardment, the sample was slowly heated to room temperature. The results show the dissociation cross-section for the formic acid of 2.4x10^-13 cm2, and half-life due to galactic cosmic rays of 8x10^7 yr. The IR spectra show intense formation of CO and CO2, and small production of more complex species at high fluences.

Measurements of the momentum distribution of high-energy electrons emitted in weakly relativistic ion-solid collisions are compared with a transport theory which is based on the relativistic electron impact approximation for electron production and which accounts for angular deflection and energy loss but also energy straggling of the transmitted electrons. The measurements on electron ejection by 45 MeV u-1 Ni28+ projectiles colliding with carbon foils of thickness 10-8300 µg cm-2 were made on an absolute scale, providing a sensitive test of the transport theory. The theory gives a satisfactory description of earlier (relative) data from 13.6 MeV u-1 Ar18+ impact on carbon. Absolute singly differential cross sections for Ni28+ agree within 10% in the case of thin targets, but the width of the binary encounter peak is underestimated by theory. For the thickest targets the measured doubly differential cross sections are overpredicted by up to one order of magnitude, particularly at forward emission angles, but peak shapes are well reproduced.

Electronic sputtering with heavy ions as a function of both electronic energy loss d E /d x and projectile charge state q was studied at the French heavy ion accelerator GANIL. Amorphous carbon (untreated, and sputter-cleaned and subsequently exposed to nitrogen) was irradiated with swift highly charged ions ( Z =6–73, q =6–54, energy 6–13 MeV/u) in an ultrahigh vacuum scattering chamber. The fluence dependence of ion-induced electron yields allows to deduce a desorption cross-section σ which varies approximately as σ ∼(d E /d x ) 1.65 or σ ∼ q 3.3 for sputter-cleaned amorphous carbon exposed to nitrogen. This q dependence is close to the cubic charge dependence observed for the emission of H + secondary ions which are believed to be emitted from the very surface. However, the power law σ ∼(d E /d x ) 1.65 , related to the electronic energy loss gives the best empirical description. The dependence on d E /d x is close to a quadratic one thus rather pointing towards a thermal evaporation-like effect.

International audience; We report on the charge dependence of electron yields from sputter-cleaned amorphous carbon targets bombarded with an isotachic set of swift ions. The experiments were performed in a UHV setup at the heavy-ion accelerator GANIL in Caen. The ion velocity was 19 a.u. (corresponding to a kinetic energy of 9.2 MeV/nucleon) and the projectile charge QP was varied from 6 to 39. As observed for ion-atom collisions, the electron yield exhibits a reduction with respect to a Q2P law. We show that this projectile charge dependence is consistent with a strong saturation of low-energy primary electron ejection. This effect is related to the primary projectile-target interaction itself and not to high-charge effects affecting the electron transport before escape from the target.

The momentum distribution of fast binary-encounter electrons emitted from solid-state targets of various thicknesses is investigated both theoretically and experimentally. The production of electrons in binary-type collisions with fast, highly stripped ions is calculated in the electron-impact approximation. A transport theory is formulated which allows for energy loss as well as angular deflection of the electrons (within the separation of energy loss and angular scattering approximation) during penetration of the target. The broadening of the binary encounter peak with increasing target thickness observed experimentally in $13.6\ensuremath{-}\mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{u}{\mathrm{Ar}}^{17+}$ and ${\mathrm{Ar}}^{18+}$ colliding with carbon foils is well described by theory.

We report on measurements of light ion (Z52) and heavy ion (Z514) induced electron emission yields from the entrance and exit surfaces of thin carbon foils near the electronic energy loss per unit path length (dE/dx) maximum. At constant dE/dx , secondary electron yields are lower for high projectile velocities than for lower projectile velocities. This velocity effect, which is well known for secondary ion emission, is observed for backward electron emission for both He and Si. In the case of Si projectiles such a velocity effect is also observed for forward electron emission. The results can be qualitatively understood in the framework of recent electron transport and nuclear track models. @S0163-1829~99!08617-8#