Surface modifications induced by high energy heavy ions on quartz (SiO2) and sapphire (Al2O3) have been studied by means of photoelectron spectroscopy and extended X-ray absorption fine structure spectroscopy. Results are interpreted in the frame of density of states calculations performed using a semiempirical tight binding method. Under oxygen ion irradiation, it appears that the induced damage consists mainly of lattice distortion plus a population of point defects identified as oxygen vacancies.

Excitation of electrons in pure amorphous and crystalline bulk SiO 2 may induce transient or stable modifications of their geometrical and electronic structure. Such situation is found either under electrons, X-rays, γ-rays, UV laser irradiation or along the path of very energetic ions (>62; MeV/amu). In turn, the bulk characteristics of the material such as loss tangent, Young's modulus can be changed. A review is given of this type of radiation effects. It includes surface studies, and bulk defect production. It has been adduced that defects production mechanism involves the self trapping of excitons. This process will be discussed in the frame of new results related to high local densities of electronic excitation.

ESR studies of amorphous silica samples irradiated by high energy heavy ions show that the paramagnetic defects formed when electronic interactions dominate are similar to those observed after γ-ray irradiation (E' centers and oxygen hole centers, or OHC). However, spectra of ion-irradiated samples exhibit specific features, due to the high density of energy deposit which is specific to heavy ion irradiation. Furthermore, the concentrations of defects cannot be interpreted from the total energy deposit alone, as the atomic number plays an important role. When the energy deposit increases, we observe a transfer from E' centers to OHC, which is also observed after annealing. This supports the concept of a “ thermal spike” reorganization phase in the wake of the incident ion. Optical spectroscopy results are consistent with ESR for E' centers, and show that the B2 centers, which are interpreted as diamagnetic oxygen vacancies, are less abundant than the E' centers.

We investigated the paramagnetic defects formed by high-energy ions in amorphous SiO2 using electron spin resonance. We show that the variation of paramagnetic defect densities with both the residual range and the atomic number of the ion is not simply correlated with the total energy deposited in the sample, which is the major controlling parameter for other types of irradiation (γ rays, electrons). This specificity of ion irradiation is most likely related to the high local density of deposited energy. The observed populations of paramagnetic defects constitute a small fraction of the formed defects. However, their characteristics can be related to results on ion track structure obtained by small-angle scattering and track etching methods.

A mission to Mars and small solar system bodies is presently studied as a possible collaboration between INTERCOSMOS, CNES, ESA and eventually other participants. The VESTA concept, based on the same strategy as the successful VEGA mission, is more ambitious, as two spacecrafts separate soon after launch: a soviet spacecraft, dedicated to the study of Mars, and a spacecraft dedicated to the study of small bodies, under the responsibility of CNES and ESA. This spacecraft would use Mars gravity assists to visit up to 4 small bodies in less than 5 years. The mission is duplicated, which means that up to 8 small bodies could be studied (e.g. 6 main belt asteroids, 1 apollo-amor asteroid and 1 short period comet). Low relative velocities (< 3.5 km/s) should allow to drop a penetrator on two large main belt asteroids, such as 4 Vesta and 1 Ceres (1994 launch).

Pure fused low-OH silica (Tetrasil SE) has been studied by electron spin resonance (ESR) after it had been irradiated by 50 MeV/amu oxygen and 43 MeV/amu krypton ions at the GANIL accelerator. Paramagnetic defects have been observed which are closely related to intrinsic defects formed by γ-ray irradiation in amorphous SiO2, such as the E′ center and the peroxy radical. ESR signatures of defects formed by heavy ions exhibit, however, specific features in comparison with those formed by other types of irradiation (γ/x rays, electrons, or neutrons). The density of defects increases faster than the energy loss, so that the production of defects by heavy ion irradiation cannot be described by the total energy deposit alone. This is consistent with previous studies of latent ion tracks in insulating minerals using small angle x-ray scattering and track etching techniques.

Implantation of low energy (~ 1 keV/amu) Pb ions, simulating α-recoils, greatly increases the dissolution rate of U-bearing minerals in aqueous solutions above a critical dose ~5 × 1012ions·cm−2. A Monte-Carlo code of etching indicates that this phenomenon corresponds to a percolation threshold due to the accumulation of ion-induced defects above a critical concentration. Such a radiationenhanced dissolution could be produced by α-recoil damage in U-rich accessory minerals of sufficient U-content and/or age. Therefore, this process could be the primary source of this element in the formation of U ores associated with crystalline rocks.

The 234U/238U disequilibrium observed in nature has been previously interpreted by means of four models based on the properties of α-recoil nuclei and on the transport of uranium isotopes by natural waters. As aqueous dissolution of minerals can potentially dilute such disequilibrium by releasing large amounts of 238U, we tentatively evaluate the ability of these models to quantitatively account for the disequilibrium within different scenarios of aqueous corrosion. We show that three of the models (ejection of recoil nuclei and derived models) require very low (and unlikely) dissolution rates while the last one (change in valence state), which does not depend on the dissolution rates, seems plausible although it has not been particularly emphasized in recent works.

High doses (> 1012 ions cm−2) of low energy (∼1 keV/amu) heavy ions produce, on insulating surfaces, thin layers of heavily damaged material (“planar tracks” ∼ 1000 Å) with an increased chemical reactivity. We have attempted to infer indirectly their defect structure in the case of muscovite mica from experiments combining thermal annealing and etching. We show that planar tracks: (i) have a multi-layered structure with respect to etchability, probably reflecting the damage profile; (ii) are constituted of randomly distributed point defects and extended defects for which an “active” diameter ~100 Å is inferred.

We first present a brief review of previous work dealing with ion-induced enhancement in etchability in various insulating materials, subjected to strong etchants. Then we describe more recent experiments performed with reference to radiation effects in radioactive waste solid forms and mostly concerning the selective dissolution regime which commonly applies to natural aqueous corrosion. The most important characteristic revealed by these studies is the occurrence of a threshold effect with increasing ion dose. In the particular case of lead ions used for simulating α-recoils, the critical dose is ∼ 5 × 1012 ions cm−2. This behavior can interpreted as a percolation effect by means of a Monte Carlo model of etching. In order to check the suitability of ion implantation for simulating internal irradiation due to α-decay, we systematically discuss the possible problems of this technique, including the effect of dose rate, surface charging and compositional changes, stress fields, etc.. We conclude that ion implantation is a versatile and powerful tool for studying radiation effects associated to α-decay in actinide-containing solids.

The annealing and etching behavior of tracks produced by 6 and 14 MeV/amu U ions was investigated both in labradorite and muscovite mica. Our results are best interpreted in terms of a continuous structure of these tracks. In particular, their annelaing is a global process dominated by the thermal stability of the region intersecting the surface.

Muscovite mica and labradorite crystals have been irradiated by 1013-1014 cm−2 protons (12 MeV) and ∼106 Fe ions (1.9 MeV/amu). Three types of samples were prepared, having received respectively: (i) Fe ions only; (ii) protons followed by Fe ions; (iii) Fe ions followed by protons. The annealing behavior of Fe tracks was studied in the three types of samples. In samples first irradiated with high doses of protons, Fe tracks anneal at a higher temperature than in the other samples. We discuss implications on track formation mechanisms and the enhanced stability of fossil tracks compared to artificial tracks.

The theoretical motion of individual dust grains in the lunar regolith is analyzed by using a Monte Carlo statistical code where the variables are the mass and speed distribution of meteorites at the lunar surface and the geometrical shape of impact craters. From these computations the detailed irradiation history of the grains in the ancient solar wind is traced back, over a period of 4 billion years, as a function of the grain size. Then by combining this irradiation scheme with the result of solar wind simulation experiments, the time and depth dependent accumulation of solar wind effects in the theoretical grains (solar wind maturation) is inferred. Finally, the validity of these predictions is tentatively checked by discussing a variety of physical and chemical solar wind effects which are registered in the surface layers of lunar dust grains. Therefore these studies give a tentative scenario for the “maturation” of the lunar regolith with respect to solar wind effects, but they also reveal useful guidelines to deduce meaningful information from such effects. In particular, they suggest a “lunar skin” sampling technique for extracting dust grains in lunar core tubes which could help in deciphering the past activity of the ancient solar wind over a time scale of several billion years.