New Attempts to Understand Nanodiamond Stardust

Abstract

Abstract:We report on a concerted effort aimed at understanding the origin and history of the pre-solar nanodiamonds in meteorites including the astrophysical sources of the observed isotopic abundance signatures. This includes measurement of light elements by secondary ion mass spectrometry (SIMS), analysis of additional heavy trace elements by accelerator mass spectrometry (AMS) and dynamic calculations of r-process nucleosynthesis with updated nuclear properties. Results obtained indicate that: (i) there is no evidence for the former presence of now-extinct 26 Al and 44 Ti in our diamond samples other than what can be attributed to silicon carbide and other 'impurities', and this does not offer support for a supernova (SN) origin but neither does it negate it; (ii) analysis by AMS of platinum in 'bulk diamond' yields an overabundance of r-only 198 Pt that at face value seems more consistent with the neutron burst than with the separation model for the origin of heavy trace elements in the diamonds, although this conclusion is not firm given analytical uncertainties; (iii) if the Xe-H pattern was established by an unadulterated r-process, it must have been a strong variant of the main r-process, which possibly could also account for the new observations in platinum.

The production of proton-rich isotopes beyond iron: The γ-process in stars

“…[93,94]). Last but most importantly, the isotopic ratio of the Xe-L isotopes is not consistent with the same ratio of these p nuclei in the solar system [95,96]. It is unknown why they are different.…”

“…The most abundant p nuclei in the Solar System is 74 Se (0.89% of the Se abundance in the Sun). In general, the solar abundances of the light p nuclei between 74 Se and 96 Ru are comparable within a factor of three to four (e.g., Ref. [34]).…”

“…Anomalies have been confirmed for the p nuclei 92,94 Mo (e.g., Refs. [98,99]), 96,98 Ru (e.g., Refs. [100,101]), 144 Sm (e.g., Refs.…”

“…As an example, Fig. 4 shows the isotopic abundances and the time-integrated absolute nucleosynthesis fluxes for Hashimoto trajectories 3 (upper panel) and 6 (lower panel) in the mass region between Zr and Cd, where the p nuclei 92,94 Mo, 96,98 Ru, 102 Pd and 106 Cd are located. The temperature profiles reach their peaks at 2.95 GK (traj.…”

Photoluminescence of silicon‐vacancy defects in nanodiamonds of different chondrites

“…Since their discovery (Lewis et al 1987), the formation process(es) and astrophysical source(s) of MND remain highly debatable despite significant efforts (see extensive review by Daulton 2005). However, isotopic composition of noble gases and, in particular, of Xe, indicates that some nanodiamonds might be related to supernovae explosions (e.g., Lewis et al 1987;Jorgensen 1988;Ott et al 2012), isotopic compositions of bulk carbon and of the principal chemical impurity-nitrogen-in the diamond-rich separates are less conclusive and may support the hypothesis that at least a fraction of MND was formed in the solar system (Dai et al 2002). Processes of MND formation are also debatable, but combined analysis of information about structure and chemical impurities (Shiryaev et al 2011) suggests that the growth process of (at least) N-containing grains should be very fast.…”