Isotopes in water

If the stable isotope ratio of 13C/12C is to be further measured in tree rings and interpreted as an indicator of climate variation, (and we have barely begun to initiate its use as a thermometer in the present work, confining our measurements to the stable isotopes in water, because water is so abundant compared to carbon dioxide and because the dependence of its isotope ratios is relatively simple compared with those of carbon dioxide), some more sophisticated considerations must be given to the distribution of carbon dioxide among the reservoirs on the surface of the earth. 

But nature provides only 0.7% of the fissionable isotope U in natural uranium, the rest being 238u and although the predominant hydrogen isotope in water is a good moderator, it absorbs too many neutrons to allow a reaction to be maintained with the low content of natural uranium. However, the heavy hydrogen... 

Earlier methods used in the analysis of radium isotopes in water required labor-intensive radiochemical separations and subsequent measurement of alpha particles for 226Ra and beta particles for 228Ra. The method used in this experiment applies simpler gamma-ray spectral analysis of the progeny of both 226Ra and 228Ra. 

Uranium in nature may be measured either radiometrically or chemically because the main isotope - 238U - has a very long half life (i.e., relatively few of its radioactive atoms decay in a year). Its isotopes in water and urine samples usually are at low concentrations, for which popular analytical methods are (1) radiochemical purification plus alpha-particle spectral analysis, (2) neutron activation analysis, (3) fluorimetry, and (4) mass spectrometry. The radiochemical analysis method is similar in principle to that of the measurement of plutonium isotopes in water samples (Experiments 15 and 16). Mass spectrometric measurement involves ionization of the individual atoms of the uranium analyte, separation of the ions by isotopic mass, and measurement of the number of separated isotopic ions (see Chapter 17 of Radioanalytical Chemistry text). 

A method of determining airborne iodine has also been reported.241 Here, iodine is absorbed into 5% aqueous KI and spectrophotometrically determined at 590 nm in the form of its complex with starch. This method is selective with respect to bromine and chlorine, and the sensitivity of this method is 0.25 mg of I2 per m3 of air. The concentration of the, 31I isotope in water can be determined by a method involving isotope exchange in the starch-iodine complex.242 Flow-injection determination of ascorbic acid (0.1-40 mg/mL) has been proposed.243 Iodine is generated in the flow system as I3- ions, which are in turn exposed to starch to produce a steady signal at 350 and 580 nm. Ascorbic acid provides inversed maxima which are measured. This method is recommended for analysis of ascorbic acid in fruit juice, jam, and vitamin-C preparations. Use of the blue complex has also been reported for determination of sodium dichloro-isocyanurate in air.244 Obviously the blue reaction is applicable in the determination of amylose, amylopectin, and starch,245-252 as well as modified starches.245,253-255... 

Pietrzak-Flis, Z., Kaminska, I., Chrzanowska, E. Uranium isotopes in waters and bottom sediments of rivers and lake in Poland. Nukleonika 49(2), 69-76 (2004)... 

Andersson P., Torssander P., and Ingri J. (1992) Sulphur isotope ratios in sulphate and oxygen isotopes in water from a small watershed in central Sweden. Hydrobiologia 235/ 236, 205-217. 

Deak J. and Coplen T. B. (1996) Identification of Pleistocene and Holocene groundwaters in Hungary using oxygen and hydrogen isotopic ratios. In Isotopes in Water Resources Management, IAEA, Vienna, vol. 1, 438p. 

Frape S. K., Bryant G., Blomqvist R., and Ruskeeniemi T. (1996) Evidence from stable chlorine isotopes for multiple sources of chloride in groundwaters from crystalline shield environments. In Symposium on Isotopes in Water Resources Management. United Nations Educational, Scientific and Cultural Organization, Vienna, pp. 19-30. 

Most common is the process of mass-dependent fractionation, in which the stable isotope ratio is altered as the consequence of physical processes differentially affecting atoms or molecules of different mass. Isotopes are fractionated relative to one another according to thermodynamic, kinetic, and diffusion processes. A simple example is the way in which oxygen isotopes in water molecules are fractionated during the process of evaporation. Water molecules containing the lower mass isotope leO are more likely to become water vapor than those containing the higher mass isotope lsO. Hence the water vapor is enriched in isotope leO and the liquid water is enriched in isotope lsO. 

These calculations show that diffusional mixing is much the slowest of all the modelled processes (Fig. 8). Methane in gas and Cj2 components in oil have the shortest diffusional mixing times, between one and ten million years, while C200 components in viscous oil and strontium isotopes in water would take ten to a hundred million years to mix diffusionally between the two reservoir segments. In these simple calculations, pure fluids were assumed. In a more rigorous treatment, fluid saturations would have to be taken into account, including for example the increased tortuosity of the water phase with high oil or gas saturations... 

Radioactive decay enables a very conditional determination of surface origin water existence duration in the geologic medium. Such estimates are based on measuring either the excess of radiogenic stable isotopes or deficit of radioactive cosmogenic isotopes in water (Kazemi, 2006). 

Padden, M.,T. W. D. Edwards R. Vance, 1996. Temperature dependent oxygen and carbon isotope fractionation between carbonate and cellulose in lake sediments Symposium on isotopes in water resources management. International Atomic Energy Agency, Vienna, 20-24 March 1995 241-244. 

Expt. No. Number of fish marked Average weight (mg) Method of marking Concentration of isotope in water ( xCi/ml) Marking time (hr) Days in flowing sea water Mean cpm/fish at end of experiment... 

Techniques for the characterization of radionuclides in aqueous solutions did not change significantly in the last years. Most of the new investigations are focused on the elimination of interferences and faster separations through the use of new products with novel physical and chemical properties. Some other applications to the analysis of radionuclides are focused on understanding natural systems through the analysis of isotope ratios. The purpose of this review is to summarize problems arising due to radionuclides in the environment and to present new techniques for the determination of isotopes in water. 

Sample preparation Hydrogen isotopes in water are measured from H2 gas formed by reducing water with a suitable reducing agent like U, Zn, Cr or C. It is also possible to exchange hydrogen isotopes between H2 gas and H2O in the presence of Pt catalysts. 

Scholtis, A., Pearson, F. J. Jr, Loosli, H. H., Eichinger, L., Waber, H. N. Lehmann, B. E. 1996. Integration of environmental isotopes, hydrochemical and mineralogical data to characterize groundwaters from a potential repository site in central Switzerland. In Proceedings of a Symposium on Isotopes in Water Resources Management AIEA (Vienne), Vol. 2, 263-280. 

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