History of trace gases in presolar diamonds inferred from ion-implantation experiments

Abstract

Diamond grains are the most abundant presolar grains found in primitive meteorites. They formed before the Solar System, and therefore provide a record of nuclear and chemical processes in stars and in the interstellar medium. Their origins are inferred from the unusual isotopic compositions of trace elements-mainly xenon-which suggest that they came from supernovae. But the exact nature of the sources has been enigmatic, as has the method by which noble gases were incorporated into the grains. One observation is that different isotopic components are released at different temperatures when the grains are heated, and it has been suggested that these components have different origins. Here we report results of a laboratory study that shows that ion implantation (previously suggested on other grounds) is a viable mechanism for trapping noble gases. Moreover, we find that ion implantation of a single isotopic composition can produce both low- and high-temperature release peaks from the same grains. We conclude that both isotopically normal and anomalous gases may have been implanted by multiple events separated in space and/or time, with thermal processing producing an apparent enrichment of the anomalous component in the high-temperature release peak. The previous assumption that the low- and high-temperature components were not correlated may therefore have led to an overestimate of the abundance of anomalous argon and krypton, while obscuring an enhancement of the light-in addition to the heavy-krypton isotopes.

New Attempts to Understand Nanodiamond Stardust

“…To complicate matters further, the Koscheev et al (2001) results -similar to observations in other ion implantation studies using different materials (e.g., Nichols et al 1992;Hohenberg et al 2002) indicate that the high-temperature part of the implanted xenon is mass-fractionated relative to the starting composition and that measured in the low temperature release, by about 1% per a.m.u (Huss et al 2008), which would then be the appropriate composition to subtract for deriving the pure from the measured Xe-H composition. In addition, if the pure Xe-H were introduced by the same kind of ion implantation, the thus derived Xe-H would differ from that in the source by the same kind of fractionation factor.…”

“…On the other hand, nanodiamonds contain also the Xe-P3 noble gas component released at low temperature (Huss & Lewis 1994) and both P3 and HL gases most likely were introduced by ion implantation (e.g., Lewis et al 1989;Verchovsky et al 2003). Experimental investigations of ion implantation into nanodiamond (Koscheev et al 2001) indicate that the implanted gases show a bimodal temperature releaseas observed in the meteoritic nanodiamonds -which then suggests that the high-temperature 130 Xe-containing component present besides the ( 130 Xe-free) pure Xe-H is the same P3 component as observed at low temperature (Huss et al 2008). In other words, it is more likely that the 'background' Xe has the P3 rather than solar composition.…”

Ion Implantation into Presolar Grains: A Theoretical Model

“…The processes are almost all mass-dependent and this will inevitably lead to a systematic isotope fractionation of implanted ions relative to their source reservoir. Such effects have been observed experimentally and in particular for noble gases (Bernatowicz et al 1987;Ponganis, Graf & Marti 1997;Koscheev, Gromov, Mohapatra et al 2001). However, these isotope effects are not necessarily dependent on grain size and are therefore not particularly related to the model under discussion.…”

The chemistry of the surface of modified detonation nanodiamonds of different types

“…In the present work, this difficulty was overcome by the use of UDD as synthetic analogues of MND. A similar approach was earlier successfully applied in experiments on ion implantation [22]. The distinguishing feature of this work is a study of the influence of the same chemical procedure used to extract diamonds from meteorites on the chemistry of the surface of nanodiamonds of different types with substantially different and characterized surface properties.…”

“…We studied CH-7o and CH-7x samples with substantially different surface properties. The implantation of argon ions of a 1 keV energy at equal doses was performed as in [22].…”