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Nanodiamonds in meteorites: properties and astrophysical context

Ott U.

Journal of Achievements in Materials and Manufacturing Engineering

2009

Vol. 37, nr 2

779-784

Purpose: This contribution provides an overview on properties and origin of nanodiamonds in primitive meteorites. Nanodiamond are a type of stardust, i.e. “pre-solar” grains that formed in the outflows or ejecta of stars. Design/methodology/approach: We summarize previously obtained results and include our results dealing with recoil loss from nanoparticles during radioactive decay of trace elements within them. Findings: Nanodiamonds in primitive meteorites have a mean size of ~2.6 nm and an abundance reaching up to ~0.15 % by weight. They contain trace noble gases, notably xenon, with an unusual isotopic composition. The latter is reminiscent of the p- and r-processes of nucleosynthesis that are thought to occur during supernova explosions. Our new results show that recoil loss during â decay of implanted 22Na does not exceed what is expected from energy distribution and range-energy relations in matter. While a CVD origin for the diamonds appears likely (but is not assured), the noble gases were probably introduced by ion implantation. Research limitations/implications: The isotopic pattern of Xe contained in nanodiamonds indicates some unconventional types of element synthesis in stars or modification by secondary processes. Recoil loss from nanometer-sized grains during decay of unstable precursor nuclides has been suggested as an explanation, but our experiments do not support this idea. Originality/value: Other processes must be invoked for explanation of the isotopically unusual xenon trapped in meteoritic nanodiamonds. Ion implantation experiments suggest of “trapped” cosmic ray 3He for deriving an age for the diamonds.

Jak kosmologia tłumaczy powstanie pierwiastków chemicznych?

Ilczyszyn M.

Wiadomości Chemiczne

1998

[Z] 52, 7-8

512-527

Cosmology is presented as a branch of science dealing with the Universe. The most important achievement in this field is the Big Bang theory accounting for the formation of the Universe by an explosion 10-25 billion years ego. This event was followed by different processes schematically divided into 'Planc', 'handron', 'lepton', 'radiation|' and 'galaxy' era (Tab. 1). Universal abundance of elements is presented as a relation between logarithm of the elements (or isobars) abundance in the solar system and the atomic (or mass) numbers (Figs 1 and 2). These relations are treated as records of the Universe evolution. Four groups of the nucleosynthesis are presented according to this idea (Tab.2):(1) primary reactions at the beginning of the Universe; (2) 'burning' of light elements inside stars; (3) neutron capture inside stars; (4) photonuclear reactions inside strongly heated-up stars, natural disintegration of heavy elements inside and outside the stars, breaking of heavy elements in the interstellar space. Light chemical elements - from hydrogen to lithium - were created during the first minutes after the Big Bang by primary nucleosynthesis processes (reactions 1-7). This mechanism is responsible for very high abundance of hydrogen (~90% of all atoms in the Universe) and helium (~9%). Heavy elements are produced up to now inside stars. Special attention is paid to description of different stages and ways of star evolution (Fig. 3) and to relations of this processes to the nucleosynthesis inside stars (reactions 8-38). These processes strongly depend on the beginning mass of the star. Stars similar to the Sun are responsible for formation of carbon and oxygen only. In the bigger ones the elements up to the iron group can be formed. In the case of the largest ones supernova phenomenon is possible: the star that has exhausted its nuclear fuel, collapses into a superdense state, and explodes with a final burst of enormous energy. This is responsible for reactions from the group (4).