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Abstract: 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 7Li+ (atomic ions) sputtered from a LiF crystal by Ca17+ (9MeV/u) and Xe21+ (17keV/q =350keV) 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. [Copyright &y& Elsevier]

Thymine (C 5 H 6 N 2 O 2) is a basic N -heterocyclic nucleobase in all known organisms, and this molecule is also found in meteoritic materials. This study aims to investigate thymine's physical and chemical modifications under ion irradiation in cryogenic conditions. Space radiation was simulated by exposing thymine at 27 K to 230 MeV 48Ca10+ ions. Fourier transform infrared spectroscopy (FTIR) was employed to monitor the degradation of a 2.8 μm thick sample film under irradiation. From the intensity decrease of the infrared absorptions as a function of ion fluence, the destruction cross-section (σ), required to dissociate or eject a thymine molecule, is deduced by an exponential function. The physical and chemical modifications induced by energetic projectiles can be related to the electronic stopping power S e as σ = S e / D 0 , where D 0 = 9.6 ± 0.4 eV/molecule is the effective mean dose needed to destroy the thymine molecule at 27 K. Also, new molecular species formed under irradiation are observed and, based on infrared spectra, identified as CN−, OCN−, HCNO, and CO. [ABSTRACT FROM AUTHOR]

Abstract: Sputtering occurs as a result of deposition of kinetic or potential energy in solids irradiated with swift particles. We studied ejection of secondary ions from LiF induced by swift heavy ion impact. A new UHV system allows measuring the mass distributions and the velocity vectors of each emitted secondary ion by means of time-of-flight and imaging techniques (XY-TOF-SIMS) with controlled target surfaces. We present results performed at GANIL (Caen) with Ca beams at 7.6 and 9MeV/u (electronic stopping regime). Under UHV conditions, particles emitted from cleaved LiF monocrystals include the omnipresent hydrogen, and the two isotopes of natural LiF (6Li+ and 7Li+). Two groups of clusters, namely and (LiF) n Li+ appear. The cluster size (n) dependence of the cluster ion yields Y(n) can be described by an exponential function. LiF emission as ionic clusters (LiF) n Li+ with n ⩾2 is dominant over emission as monomers LiFLi+. [Copyright &y& Elsevier]

Abstract: 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 (∼50–500MeV) in the electronic energy loss regime, and to compare them with those produced by protons, photons, and electrons. Our results for and CO indicate that sputtering induced by heavy ions can be an important mechanism to desorb molecules in astrophysical environments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

N 2 O and CO 2 can be formed in the interstellar space and in ices on the surface of outer solar system bodies, such as Pluto and Triton. Energetic ions can simulate the energy transfer processes that occur by cosmic ray irradiation of interstellar ices, comets, and icy solar system bodies. Proceeding systematic research, pure nitrous oxide (N 2 O) ice, and nitrous oxide and carbon dioxide (CO 2) ice mixture were irradiated at 11 K with MeV-nitrogen (N+) and -xenon (Xe23+) ion beams. The chemical and physical effects induced by ion irradiation on the N 2 O ice and the N 2 O:CO 2 ice mixture are compared. The formation and dissociation cross sections scale with the electronic stopping power (S e) roughly as σ ∼ a S e n, where n ∼ 3/2. The n power law is helpful for predicting the N 2 O formation and dissociation cross-sections for other ion beam projectiles and energies; these predictions will allow estimating the effects of the entire cosmic ray radiation field. [ABSTRACT FROM AUTHOR]

Single crystal graphite was irradiated by slow, highly charged ions. The modification of the surface structure was studied by means of Low-Energy Electron Diffraction. The observed damage cross section increases with the potential energy, i.e . the charge state of the incident ion, at a constant kinetic energy. The potential energy is more efficient for the damage production than the kinetic energy by more than a factor of twenty. Comparison with earlier results hints to a strong link between early electron creation and later target atom rearrangement. With increasing ion fluence, the initially large-scale single crystal is first transformed into μ m-sized crystals, before complete amorphisation takes place. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In the relatively shielded environments provided by interstellar dense clouds in our Galaxy, infrared astronomical observations have early revealed the presence of low temperature (10–100 K) ice mantles covering tiny grain “cores” composed of more refractory material. These ices are of specific interest because they constitute an interface between a solid phase under complex evolution triggered by energetic processes and surface reactions, with a rich chemistry taking place in the gas phase. The interstellar ice mantles present in these environments are immersed, in addition to other existing radiations fields, in a flux of cosmic ray particles that can produce new species via radiolysis processes, but first affects their structure, which may change and also induces desorption of molecules and radicals from these grains. Theses cosmic rays are simulated by swift ions in the laboratory for a better understanding of astrophysical processes. [ABSTRACT FROM AUTHOR]

Abstract: The effect of solar wind on cometary ice was studied by using oxygen ions with energy near to that corresponding to their maximum abundance in space for bombarding CO ice. This gas was condensed on a CsI substrate at 14K and irradiated by 28keV 18O6+ ions up to a final fluence of 1.3×1016 cm−2. We have used a methodology in which the sputtering yields, the destruction rate of CO, and the rate of formation of new molecular species are determined by Fourier transform infrared spectroscopy (FTIR). In the current experiment, the condensation of a thin water ice film has prevented the CO sputtering. Quantities such as the dissociation yield, Y d (the number of ice molecules destroyed or dissociated per projectile impact), and the formation yield, Y f (the number of daughter molecules of a given species formed per projectile) are found to be more appropriate and useful than using an integrated or average cross section, since the projectiles are slowing down in the ice from their initial energy until zero velocity (implantation). [Copyright &y& Elsevier]

Abstract: A thin germanium crystal has been irradiated at GANIL by Pb beams of 29MeV/A (charge state Q in =56 and 72) and of 5.6MeV/A (Q in =28). The induced ion emission from the sample entrance surface was studied, impact per impact, as a function of Q in, velocity vin and energy loss ΔE in the crystal. The Pb ions transmitted through the crystal were analyzed in charge (Q out) and energy using the SPEG spectrometer. The emitted ionized species were detected and analyzed in mass by a time-Of-flight multianode detector (LAG). Channeling was used to select peculiar ΔE values in Ge and hence peculiar Pb ion trajectories close to the emitting entrance surface. The experiment was performed in standard vacuum. No Ge emission was found. The dominating emitted species are H+ and hydrocarbon ions originating from the contamination layer on top of the crystal. The mean value 〈M〉 of the number of detected species per incoming Pb ion (multiplicity) varies as (Q in/vin ) p , with p values in agreement with previous results. We have clearly observed an influence of the energy deposition ΔE in Ge on the emission from the top contamination layer. When selecting increasing values of ΔE, we observed a rather slow increase of 〈M〉. On the contrary, the probabilities of high multiplicity values, which are essentially connected to fragmentation after emission, strongly increase with ΔE. [Copyright &y& Elsevier]

Abstract: In order to study the sputtering of secondary ions from well characterized surfaces, we constructed a new UHV system named AODO. It consists of a detector chamber, a target preparation and analysis chamber, and a target transfer rod. We present the lay-out of this new instrument. The detector allows measuring the time-of-flight of emitted secondary ions and their position on a 2D imaging detector (XY-TOF imaging technique). The analysis chamber can be used to study surface modification by means of LEED (low energy electron diffraction). We show preliminary results of the evolution of the LEED patterns as a function of the projectile fluence during irradiation of HOPG (highly oriented pyrolytic graphite) with slow Xe14+ ions at ARIBE (the low energy, highly charged ion beam line of the French heavy ion accelerator GANIL). [Copyright &y& Elsevier]