In situ characterization of irradiation-induced microstructural evolution in urania single crystals at 773 K

International audienceImplantations with low-energy ions (Xe, La) on UO2 single crystals at 773 K were performed to investigate the role played by both the radiation damage and the incorporation of foreign elements on the matrix destabilisation. The radiation damage was monitored by both in situ RBS-C and in situ TEM during ion irradiation experiments performed at 773 K. RBS-C data shows a similar regular increase of the radiation-induced disorder in crystals for both Xe and La ions followed by a saturation plateau at about 3–4 dpa. An unexpected difference of the value of the saturation plateaus is observed, with a higher value recorded for Xe-irradiated crystals. In situ TEM images show the apparition and evolution of several defects as a function of the ion dose up to 40 dpa, irrespective of the nature of the bombarding ion: ‘black dots’ defects, dislocation loops and lines, and finally a dislocation network at high dpa. Nanometre-sized gas bubbles were observed at 773 K for the Xe-implanted crystal for doses larger than 3 dpa. Neither precipitate nor cavity were observed on La-implanted crystals. The difference in the saturation plateau as seen by RBS-C can be ascribed to the formation of the Xe aggregates that lead to an increase of the dechannelling yield

Micrometeorite mass flux measurements at Dome C, Antarctica

International audienc

Interstellar and interplanetary carbonaceous solids in the laboratory

International audienceThe interstellar medium (ISM) is a physico-chemical laboratory where extreme conditions are encountered and whereparticular environmental parameters (e.g., density, reactant nature, radiation, temperature, time scales) define the compositionof matter. With present observational possibilities, the fundamental question regarding the possible link betweenISM and solar system samples can be addressed by astrophysicists, planetologists, and cosmochemists. This article focuseson observations of diffuse ISM and dust components of molecular clouds, setting constraints on the composition oforganic solids and large molecules associated with matter cycling in the Galaxy. This study aims at drawing somecommonalities and differences between the materials found in the Solar System and those found in interstellar dust

Micrometeorite collections: a review and their current status

Micrometeorites are estimated to represent the main part of the present flux of extraterrestrial matter found on the Earth’s surface and provide valuable samples to probe the interplanetary medium. Here, we describe large and representative collections of micrometeorites currently available to the scientific community. These include Antarctic collections from surface ice and snow, as well as glacial sediments from the eroded top of nunataks—summits outcropping from the icesheet—and moraines. Collections extracted from deep-sea sediments (DSS) produced a large number of micrometeorites, in particular, iron-rich cosmic spherules that are rarer in other collections. Collections from the old and stable surface of the Atacama Desert show that finding large numbers of micrometeorites is not restricted to polar regions or DSS. The advent of rooftop collections marks an important step into involving citizen science in the study of micrometeorites, as well as providing potential sampling locations over all latitudes to explore the modern flux. We explore their strengths of the collections to address specific scientific questions and their potential weaknesses. The future of micrometeorite research will involve the finding of large fossil micrometeorite collections and benefit from recent advances in sampling cosmic dust directly from the air. This article is part of the theme issue ‘Dust in the Solar System and beyond’