Forsterite Amorphisation by Ion Irradiation: Monitoring by Infrared Spectroscopy

Abstract

We present experimental results on crystal--amorphous transition of forsterite (Mg2SiO4) silicate under ion irradiation. The aim of this work is to study the structural evolution of one of the most abundant crystalline silicates observed in space driven by ion irradiation. To this aim, forsterite films have been sythesised in laboratory and irradiated with low energy (30--60 keV) ion beams. Structural changes during irradiation with H+, He+, C+, and Ar++ have been observed and monitored by infrared spectroscopy. The fraction of crystalline forsterite converted into amorphous is a function of the energy deposited by nuclear collision by ions in the target. Laboratory results indicate that ion irradiation is a mechanism potentially active in space for the amorphisation of silicates. Physical properties obtained in this work can be used to model the evolution of silicate grains during their life cycle from evolved stars, through different interstellar environments and up to be incorporated in Solar System objects.

14 pages, 7 figures, to be published in A&A

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• The crystalline fraction of interstellar silicates in starburst galaxies
• Studying the Evolution of Warm Dust Encircling BD +20 307 Using SOFIA
• Micron-sized forsterite grains in the pre-planetary nebula of IRAS 17150-3224 - Searching for clues on the mysterious evolution of massive AGB stars
• Hard X-ray irradiation of cosmic silicate analogs: structural evolution and astrophysical implications
• Photoluminescence in amorphous MgSiO_3 silicate
• Irradiation induced mineral changes of NWA10580 meteorite determined by infrared analysis