Diamond isotopically enriched

Fig. 3.17. Carbon isotopic enrichment factors for aragonitic (dots) and calcitic (circles) foraminifera and inorganic precipitates as a function of temperature. Shown are the inorganic precipitate data of Baertschi (1957)- circle with dot Emrich et al. (1970)- large dots and Rubinson and Clayton (1969) revised - see text aragonite - solid diamond, calcite - hollow diamond. (After Grossman, 1984.)...

One process for synthesizing diamond uses methane in which the carbon atom is a carbon-12 isotope enriched to 99.97% Inthis process,... 

TR Anthony, WF Banholzer, IF Fleischer, L Wei, PK Kuo, RL Thomas, RW Pryor. Thermal diffusiv-ity of isotopically enriched C diamond. Phys Rev B 42 1104, 1990. 

The semiconductors that have been the subject of numerous investigations in bulk, alloyed, or nanocrystalline form include Si, Ge, doped diamond, SiC, (B, Al, Ga, In)(N, P, As, Sb), and (Zn, Cd, Hg, Pb)(0, S, Se, Te). Nature has been exceptionally benign in providing NMR-active isotopes at natural abundances exceeding 4% for all of the preceding elements except in the cases of 13C, 33S, and 170, and enrichment with isotopic-labels has become more common. 

Figure 12. Extent of dissolution and re-precipitation between aqueous Fe(III) and hematite at 98°C calculated using Fe-enriched tracers. A. Percent Fe exchanged (F values) as calculated for the two enriched- Fe tracer experiments in parts B and C. Large diamonds reflect F values calculated from isotopic compositions of the solution. Small circles reflect F values calculated from isotopic compositions of hematite, which have larger errors due to the relatively small shifts in isotopic composition of the solid (see parts B and C). Curves show third-order rate laws that are fit to the data from the solutions. B. Tracer experiment using Fe-enriched hematite, and isotopically normal Fe(lll). C. Identical experiment as in part B, except that solution Fe(lll) is enriched in Te, and initial hematite had normal isotope compositions. Data from Skulan et al. (2002).

Figure 5. Relative abundances of the Kr, Xe isotopes (Huss and Lewis 1994) in presolar diamonds have been measured in bulk samples (= many grains) and are plotted relative to solar wind abundances. The terrestrial atmosphere is shown for comparison and displays a pattern close to mass dependent fractionation relative to the solar wind. The primary nucleosynthetic processes at the origin of the different nuclei are also listed. Both Kr and Xe are elevated in the r-process isotopes, whereas only Xe is also enriched in the p-isotopes. These patterns are a strong argument in favor of a supernova origin for the diamonds. Ne isotopes in presolar diamond is within the field of bulk meteorite data.

Diamonds are host to the HL component, named because it is enriched in both heavy and light isotopes of xenon (Fig. 10.10b). The high abundances of heavy isotopes suggest r-process nucleosynthesis, whereas the abundant light isotopes suggest the -process. Both the r- and -processes occur in supemovae. However, it is not obvious why products of the two nucleosynthetic processes would be coupled, and this remains a subject of current research. Diamonds also contain other, less-anomalous noble gas components... 

For example, terrestrial Xe has typically been modeled as starting with a primordial U-Xe composition (very similar to solar wind Xe), and then experiencing (a) isotopic fractionation, (b) addition of radiogenic Xe, and (c) addition of heavy Xe isotopes derived from fission of (Pepin 2000). Martian Xe doesn t quite work that way. Swindle et al. (1986) first pointed out that U-Xe (Pepin 2000) will not work as the primordial Martian Xe. Instead, they found that except for an enrichment of radiogenic Xe, Martian atmospheric Xe could be modeled as isotopically fractionated AVCC Xe (at the time considered a primitive component, now considered a mixture of Q-Xe and Xe from presolar diamonds (Ott 2002, this volume)). In that model there would be no need for any " " Pu fission Xe. In fact, there would be no room for any. This would be strange because " " Pu has a longer half-life than the I would decay away first, yet... 

It must be concluded that the extensive research on rare gases in diamond has provided considerable information regarding isotopic effects in the mantle, perhaps related to environments unusually enriched in trace elements. However, it appears that no constraints regarding mantle rare gas components in the early Earth have been obtained. 

Figure 6 Progressive enrichment of isotopically exotic Xe components led to the discovery of interstellar diamond and SiC. The light and heavy components of Xe-HL cannot be produced in the same nucleosynthetic event and are probably the result of mixing. The Xe-S component from SiC reflects a mixture between the composition produced in s-process nucleosynthesis and a near-normal component of Xe.

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