Isotopic fractionation cosmic

With the exception of a few special cases, the isotope ratios in meteorites are the same as on the earth, which means that during the formation of the various parts of the solar system only some fractionation of the elements occurred, but no isotope fractionation. Differences in the isotope ratios in meteorites and on the earth can be explained by radioactive decay, nuclear reactions triggered by cosmic radiation and some isotope fractionation of light elements. 

Davis A. M., Clayton R. N., Mayeda T. K., and Brownlee D. E. (1991a) Large mass fractionation of iron isotopes in cosmic spherules collected from deep-sea sediments. Lunar Planet. Sci. XXII. Lunar and Planetary Institute, Houston,... 

O Neil JR (1986) Theoretical and experimental aspects of isotopic fractionation. In Valley JW, Taylor HP Jr, O Neil JR (eds) Stable Isotopes in High Temperatirre Geological Processes. Rev IVtoeral 16 1-40 O Neil JR, Clayton RN (1964) Oxygen isotope geothermometry. In Isotope and Cosmic Chemistry (eds., H. Craig et al.) North-Holland, Amsterdam, pl57-168... 

Figure 8. Ne data from 4 lunar and 2 meteoritic samples containing solar noble gases. Gases were released by in vacuo etching, except for samples 10084 (stepwise heating) and 61501 (total fusion of aliquot samples previously etched off-line). Besides solar wind Ne (SW), all samples appear to contain a second solar component, labeled SEP. This is indicated e. g. by the many points on the mixing line SEP-GCR, where GCR represents the composition of Ne produced by Galactic Cosmic Rays. The Ne/ Ne ratios above the SW point in the first release fractions of 10084 (inset) indicate isotopic fractionation during gas extraction, which is not observed in the etch-experiments. Data sources listed in Wieler (1998). [Used by permission of Kluwer Academic Publishers, from Wieler (1998), Space Sci. Rev., Vol. 85, Fig. 1, p 304.]...

Many of the molecular species detected in dense interstellar clouds are seen to contain the rare (heavy) isotopes of some elements (e.g. D, C, etc.). However, at first sight the abundance ratios of some molecules containing the rare and common isotopes (e.g. DCN/HCN) were very surprising because they are orders-of-magnitude greater than those expected from their cosmic isotopic ratios. Following extensive SIFT studies, it is now understood that this is due to the phenomenon of isotope fractionation in gas phase ion-molecule reactions. This phenomenon is exemplified by the elementary reaction ... 

Most CO and CO2 in the atmosphere contain the mass 12 isotope of carbon. However, due to the reaction of cosmic ray neutrons with nitrogen in the upper atmosphere, C is produced. Nuclear bomb explosions also produce C. The C is oxidized, first to CO and then to C02 by OH- radicals. As a result, all CO2 in the atmosphere contains some 0, currently a fraction of ca. 10 of all CO2. Since C is radioactive (j -emitter, 0.156 MeV, half-life of 5770 years), all atmospheric CO2 is slightly radioactive. Again, since atmospheric CO2 is the carbon source for photos5mthesis, aU biomass contains C and its level of radioactivity can be used to date the age of the biological material. 

The most abundant isotope is which constitutes almost 99% of the carbon in nature. About 1% of the carbon atoms are There are, however, small but significant differences in the relative abundance of the carbon isotopes in different carbon reservoirs. The differences in isotopic composition have proven to be an important tool when estimating exchange rates between the reservoirs. Isotopic variations are caused by fractionation processes (discussed below) and, for C, radioactive decay. Formation of takes place only in the upper atmosphere where neutrons generated by cosmic radiation react with nitrogen ... 

Figure 2.15 Ne three-isotope plot for a grain-size suite of plagioclase separates from lunar high land soil that were treated by the CSSE treatment (see text). The best fitted line through the data from all etched samples (line p) passes close to the data point GCR (galactic cosmic ray) of cosmogenic Ne. On the left side, the path of mass fractionation of SWC (solar wind composition)-Ne intersects line p at a 20Ne/22Ne ratio of -11.3, which is interpreted to represent SEP (solar energetic particle) Ne (cf. Section 2.8). Open symbols unetched sample. Solid symbols etched samples. SF Solar flare Ne. Reproduced from Signer et al. (1993).

Calcium-aluminum-rich inclusions (CAIs) After removing the progressive mass-dependent fractionation that occurs in the measuring process and in the formation process for the samples, isotopic anomalies for 7°Zn are observed in certain types of CAIs ( FUN inclusions). Only one detection exists to date, a deficit of 2 parts per thousand for 7°Zn in one FUN inclusion. An excess of 1.7 parts per thousand for 66Zn exists in that same CAI. Some form of cosmic chemical memory (see Glossary) is probably involved. 

Herzog G. E., Hall G. S., and Brownlee D. E. (1994) Mass fractionation of nickel isotopes in metaUic cosmic spheres. Geochim. Cosmochim. Acta 58, 5319-5323. 

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