engleski

Micro-analytical methods for the elemental analysis of micrometeorites and impact spherules

Micrometeoroids are microscopic particles moving in the interplanetary space of the Solar System. Micrometeorites are micrometeoroids that survive hypervelocity impact with the Earth's upper atmosphere and are collected at the Earth's surface [1]. Impact glass spherules are formed from melt and vapor-condensate droplets during the impact of large extraterrestrial body and are ejected at the distance grater than 10 crater diameters [2]. Impact particles found in Croatia were analyzed at the Rudjer Bošković Institute Accelerator facility using PIXE Spectroscopy in high vacuum at the ion micro-beam end-station. The 2 MeV proton beam of about 50 pA current was focused to several μm in size and positioned on selected areas on samples. X-rays from the selected areas of the samples were collected by PGT Si(Li) detector with 8.4 μm thin Be window and Al "funny filter" (75 μm thick with 2.4 % hole area). Quantitative analysis of collected PIXE spectra was performed using fundamental parameter approach with GupixWIN Software [3]. Iterated matrix solution algorithm was used assuming that all the elements are present as oxides with the option of normalization to 100%, except in the case of metallic droplet where it was assumed that invisible elements were not present. Glass standard NIST 620 was used for calibration. Surface morphology and elemental analyses (EDS) were performed on JEOL JSM-6300 SEM coupled with Oxford Instruments EDS at the University of Pécs in Hungary. Analyzed samples can be divided in two main types by their chemical composition: silicate and iron spherules. Impact glass spherules can be correlated with target rocks and causative impact event after their elemental composition [4-6]. Iron spherules provide information about chemical composition of their source objects. Impact spherules are characteristic products of impact events and they can contribute to the impact event database and provide direct correlation between impacts and geological events.

Micro-PIXE ; EDS ; glass spherules ; iron spherules

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