In the context of dust collections in space, the COMET experiment (Collecte en Orbite de Matière ExtraTerrestre) was proposed in 1982 and has been accepted in 1985 in the framework of the Soviet-French space cooperation program. The idea of such an experiment was to install collectors inside hermetic boxes, to have these boxes mounted outside a space station, orbiting the Earth and to have the capability of chosing the date and duration of the collection. In February 94, it has been proposed to fly an improved version of this instrument, as part of the payload of the EUROMIR 95 mission. Renamed as the European Space Exposure Facility (ESEF), it carries experiments from several principal investigators (PIs). These experiments have been designed to analyse in real time some parameters of the encountered particles and to collect material, both of terrestrial and extraterrestrial origin, to be brought back to the Earth at the end of the mission. Three types of collecting material are used: high purity metals, foams and silica aerogels. All grains down to submicron sizes can be possibly identified by such a variety of collectors; the presence of very low density collectors, like the foams and silica aerogels, should permit the collection of grains least modified, one of the primary goals of this investigation. This paper refers to the description of the instrument and of the various experiments.

The RBS and channeling technique was used to study the correlation between ion beam mixing and amorphization in a Zr/Ni bilayer bombarded at low temperature with several noble gas ions. The amount of mixed atoms was found to increase linearly with the ion fluence, regardless of the nuclear energy density deposited by the ion beam. The channeling results demonstrate that the number of Zr atoms mixed into the Ni substrate monitors amorphization. A description of the spatial evolution of the amorphous layer formed by ion mixing is presented.

The COMET program is a program for the collection of micron to submicron interplanetary dust particles in low Earth orbits. Since collection takes place as the Earth crosses a given meteor stream, the particles are mainly of cometary origin. The grain remnants, located at their impact positions on high purity metallic collectors, are analysed in the laboratory for chemical and isotopical identification. The COMET-1 experiment took place in 1985 October, during encounter with the Draconid meteor stream, related to the Giacobini-Zinner comet. The fluence of extraterrestrial grains that had impacted our detectors was approximately 10x higher than the value of the mean meteroid fluence at approximately 1AU, which suggests that most of the grains originated from the Giacobini-Zinner comet. One of the most important results of their chemical analysis was that approximately 90% of them are enriched in low Z elements (C and O have undoubedly been identified). They could contain a CHON phase similar to that observed in the close environment of Halley's nucleus. The first imagery of the grain remnants by field emission scanning electron microscopy suggests that they are very law density aggregates still present at the impacting positions which, in most cases, are very different from the impact craters observed for the same mean relative velocity for full grains of the same size. These results show that the COMET program has constituted an important step towards the analysis of cometary material and the understanding of the evolution of the early Solar System.

Ion beam mixing and amorphization were simultaneously studied via in situ Rutherford backscattering and channelling experiments in a Ni single crystal covered with a thin Zr layer and bombarded at liquid-nitrogen temperature with 250 keV Kr ions. The formation of the amorphous phase was found to be directly related to the number of Zr atoms mixed into the Ni crystal. The thickness of the amorphous layer can be derived from both the channelling data and the spatial extension of the Zr profile. Comparative features of amorphization induced by either ion irradiation, ion implantation or ion beam mixing are also discussed.

We describe an image-processing equipment designed and built to meet the specific requirements of an astrophysical experiment, but having probably useful applications in other fields of science and technology. It locates and makes the inventory of specified micrometer-sized holes in thin metallic films. The data acquisition is made by a CCD camera looking at the film through an optical microscope. The information goes to a microcomputer through a special interface. The program and the electronics were designed for optimum acquisition speed, automatic operation, and minimum need for human intervention.

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.

Solar wind and cosmic and cosmic ray irradiation of grains induces physical and chemical effects including their erosion and the synthesis of molecular compounds within the implanted layers. The experiments performed with H2O ice implanted by keV ions are presented. The ion implantation is intended to simulate the irradiation of comets, ring grains, and satellites of outer planets, either by the primitive solar particles or by contemporary solar wind (SW) or solar cosmic rays (SCR) fluxes. The detection of molecules was obtained through in-situ infrared spectroscopy. A model is proposed for the formation of organic matter within icy solar system bodies which is in agreement with experimental results of erosion rates. The organic molecules, frozen-in within the icy mantles of the grains present in the protosolar nebula, would originate from their primitive irradiation. Such an irradiation would have taken place during an early stage of the proto-sun, when both the SW and SCR particles were more intense by orders of magnitude.

The ion implantation-based simulation of α-recoil aging in radwaste glasses has been applied to several simulated HLW glasses. The results are qualitatively described by a new model of leaching for the implanted glasses although several specific features of irradiated surfaces are not clearly understood. This model suggests that for the most likely case of diffusion-controlled corrosion, where the reaction scheme involves several steps (hydration, dissolution of hydrated silica gel, etc…), the kinetics-controlling one would not necessarily be radiation sensitive. Indeed for these more representative glasses, no evidence for a drastic increase in the dissolution rate of the silica gel, induced by ion implantation has been so far detected, whereas the hydration rate seems in some cases more significantly enhanced. However the implications of these observations for the durability of the glasses remain to be assessed.

Most insulator materials so far proposed for storing high-level radioactive wastes, such as glass and and the constituent minerals of ceramics are nuclear track detectors. Lead ion implantation experiments show that such materials should be transformed into “giant” nuclear tracks, when the internal fluence of heavy recoils emitted during the α-decay of actinide elements stored in them exceeds a critical value, which corresponds to an equivalent storage period of a few thousand years for the wastes expected from a pressurized water reactor. In contrast, actinide bearing minerals are much more stable against α-recoil damage. As nuclear tracks are extremely chemical reactive, α-recoil damage is expected to shorten the lifetime of storage materials such as glass and ceramics against dissolution in ground waters. Fortunately new nuclear track concepts are already yielding guidelines for predicting and improving the long-term stability of storage materials. The results of the present studies also bear on the physics of ion implantation phenomena an insulator targets exposed to high fluences of low energy ions.