Isotopes content

Replacement of halides with deuterium gas in the presence of a surface catalyst is a less useful reaction, due mainly to the poor isotopic purity of the products. This reaction has been used, however, for the insertion of a deuterium atom at C-7 in various esters of 3j -hydroxy-A -steroids, since it gives less side products resulting from double bond migration. Thus, treatment of the 7a- or 7j5-bromo derivatives (206) with deuterium gas in the presence of 5% palladium-on-calcium carbonate, or Raney nickel catalyst, followed by alkaline hydrolysis, gives the corresponding 3j3-hydroxy-7( -di derivatives (207), the isotope content of which varies from 0.64 to 1.18 atoms of deuterium per mole. The isotope composition and the stereochemistry of the deuterium have not been rigorously established. 

Pu-239 is used as a fast reactor fuel, in nuclear weapons, and frequently in chemical research where production grade material of mixed isotopic content is suitable. Available enrichments range from 99.99+% to 97%. 

Metges, C, Kempe K. and Schmidt, H.-L. 1990 Dependence of the carbon-isotope contents of breath carbon dioxide, milk, serum and rumen fermentation products on the 8 Cvalue of food in dairy cows. British Journal ofNutritim 63 187-196. 

Conversion electron Mossbauer spectroscopy (CEMS) measurements with back scattering geometry have the merit that spectra can be obtained from a sample with much less isotope content compared with transmission measurements. Another merit is that a sample, deposited on a thick substrate, could be measured, and that because of the limited escape depth of the conversion electrons, depth-selective surface studies are possible. The CEMS technique was found to be best applicable to specimens of 10-100 pg Au cm, i.e., about two orders of magnitudes thinner than required for measurements in transmission mode [443]. This way (1) very thin films of gold alloys, as well as laser- and in beam-modified surfaces in the submicrometers range of depth [443], and (2) metallic gold precipitates in implanted MgO crystals [444] were investigated. 

Min GR, Edwards RL, Taylor FW, Recy J, Gallup CD, Beck JW (1995) Annual cycles of U/Ca in corals and U/Ca thermometry. Geochim Cosmochim Acta. 59 2025-2042 Moore WS (1981) The thorium isotope content of ocean water. Earth Planet Sci Lett 53 419-426 Moran SB, Hoff JA, Edwards RL, Landing WM (1997) Distribution of Th-230 in the Laborador Sea and its relation to ventilation. Earth Planet Sci Lett 150 151-160 Muhs DR, Simmons KR, Steinke B (2002) Timing and warmth of the Last Interglacial period new U-series evidence from Hawaii and Bermuda and a new fossil compilation for North America. Qrrat Sci Rev 21 1355-1383... 

Mechanisms of the formation of the decal ins in the recovered solvent were based on their isotopic contents. The cis-Decalin-die had a greater protium content than the recovered Tetralin-di2-This suggested that hydrogen transfer from the coal to the tetralin is involved in the formation of cis-Decalin. 

Administration203 to chicks of acetic acid labeled with C14 (in the carboxyl group) gave D-glucose (from the glycogen) labeled equally at C3 and C4, but the D-ribose (from nucleic acids) had more label at C3 than at C2, indicating that in vivo D-ribose does not arise exclusively from hexose by loss of Cl. The 20-30% isotope content of D-ribose formed from D-glucose-l-C14 by Escherichia coli indicates that direct conversion is the major pathway but that a part is probably derived from transketolase action.204 206... 

We can predict the oxygen and carbon isotopic compositions of the dolomite produced by this reaction path, using the techniques described in Chapter 19. Figure 25.4 shows the compositions of calcite and dolomite cements in the Lyons, as determined by Levandowski et al. (1973). The calcite and dolomite show broad ranges in oxygen isotopic content. The dolomite, however, spans a much narrower range in carbon isotopic composition than does the calcite. 

The natural cycle of carbon involves compounds of the atmosphere, hydrosphere, lithosphere, and biosphere. A certain difference in the 13C isotope content exists between the samples, depending on their origin. To estimate the deviation from the average value of 13C isotope contents 8(%o) scale is used. The deviation may be calculated by Equation 5.14 ... 

Figure 2.3 Changes in the heavy isotope content of oxygen and hydrogen in the urine with time after administration of The and 0 are diluted by the formation of H2O from oxidation of fuels and particularly that ingested in food and drink. The 0 in water is diluted from the production of CO2 via the oxidation of the fuels. The difference in the slopes indicates the rate of CO2 production. The label heavy isotope content is actually the isotopic enrichment. Physical activity, for example, increases fuel oxidation (i.e. respiration) and therefore greater dilution of...

Naudet, R. Renson, C. 1975. Resultats des analyses systematiques de teneurs isotopiques de I uranium. Results of systematio analyses of isotopic content of uranium. In Le phenomena d Oklo—The Oklo phenomenon Internatinal Atomic Energy Agency, Vienna, Austria (AUT). SCHAUBLE, E.A. 2007. Role of nuclear volume... 

As an example, for the relationship between the content of an isotope in % and the 5-value in %o. Fig. 1.9 demonstrates that large changes in the 5-value only involve very small changes in the heavy isotope content (in this case the 0 content). An ideal standard used worldwide as the zero-point on a 5-scale should satisfy the following requirements ... 

The isotopic composition of ocean water has been discussed in detail by Craig and Gordon (1965), and Broecker (1974). It is governed by fractionation during evaporation and sea-ice formation and by the isotope content of precipitation and runoff entering the ocean. 

Thode HG, Macnamara J, Collins CB (1949) Natural variations in the isotopic content of sulphur and their significance. Can J Res 27 361... 

The phenyl azide so obtained was reacted with phenylmagnesium bromide to give diazoaminobenzene, which, in turn, was split into aniline and ammonia. Determination of the isotope content of the reaction products proved that the only linear formula that fits is that in which the extreme nitrogen is the isotope 15N ... 

Assuming these probabilities are independent of isotopic content, the six isotopic adsorbed ethylenes, denoted A1 - A6 and the twelve isotopic ethyl radicals, denoted B, - Bl2, are related by a series of simultaneous equations of the form ... 

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