Lead incorparation mechanism in LiF crystals

The kinetics of doping of LiF with Pb has been described by using ab initio structural modeling methods. By calculating the formation energy of several complexes involving Pb ions (Pb • Li and Pb •• I ) and V ′ Li, it is shown that the presence of charge-balancing vacancies ease the metal incorporation in the crystal. Then, the metal captures the vacancies to form a nal stable complex Pb • Li + V ′ Li−n). These predictions are conrmed by local structure data around Pb ions derived from X-ray Absorption Spectroscopy

Simulation of low-velocity bombardment of asteroid surfaces: regolith formation and reddening of the spectra

Aims.The association of the most abundant population of meteorites, the ordinary chondrites, and the S-type asteroids through the comparison of their reflected spectra in the visible and near infrared spectrum, is still widely debated. Many asteroids show reddened spectra. To date, this reddening has been attributed to the presence of metallic nanoparticles, produced by the vaporization of Fe-bearing silicates or by a shock-induced phase transformation of metallic Fe-Ni alloys. Both the mechanisms are suggested to be related to impacts on asteroid surfaces. We show how sculpting by low-energy impacts can play an important role in the reddening of asteroid surfaces. Methods.We used quartz micro-spheres impacting on ordinary chondrites to simulate the sculpting of airless bodies due to the low-energy bombardment of micro-meteoroids. Results.The bombarded surfaces show that metals in ordinary chondrites maintain their dimensions while silicates are comminuted. Moreover, the spectra of the simulated surface are redder than traditional powdered meteorites