Oxygen isotopes, separation

Laser isotope separation techniques have been demonstrated for many elements, including hydrogen, boron, carbon, nitrogen, oxygen, sHicon, sulfur, chlorine, titanium, selenium, bromine, molybdenum, barium, osmium, mercury, and some of the rare-earth elements. The most significant separation involves uranium, separating uranium-235 [15117-96-1], from uranium-238 [7440-61-1], (see Uranium and uranium compounds). The... 

Let us fix attention on a particular H20 molecule A in the interior of water (if we wish to identify this molecule we can suppose that it contains a nucleus of the oxygen isotope 01S) and let us consider the water molecules which happen to be nearest neighbors of this molecule at the moment. These molecules have been in contact with A for different lengths of time. Since all the molecules in the liquid wander about, there was a time when none of these molecules was in contact with A. Further, if we could now begin to watch these molecules, we should find that, after the lapse of different periods of time, they become separated from A and each is replaced by another molecule. Similar remarks can be made about the molecules which come into contact with any chosen molecule. We can now raise the question—-What is the rate of turnover of this process The rate depends on the degree of local order and disorder, which in turn depends on the strength and character of the forces between adjacent molecules. 

Terabe, S., Yashima, T., Tanaka, N., and Araki, M., Separation of oxygen isotopic benzoic acids by capillary zone electrophoresis based on isotope effects on the dissociation of the carboxyl group, Anal. Chem., 60,1673, 1988. 

Romanek CS, Grossman EL, Morse JW (1992) Carbon isotopic fractionation in synthetic aragonite and calcite Effects of temperature and precipitation rate. Geochim Cosmochim Acta 56 419-430 Rowe MW, Clayton RN, Mayeda TK (1994) Oxygen isotopes in separated components of Cl and CM meteorites. Geochim Cosmochim Acta 58 5341-5347... 

Whole-rock 6 0 values can be acquired from homogenized rock samples, or from separates of individual rock-forming minerals. When 6 0 data of individual minerals are available, the oxygen isotope systematics of the rock-forming minerals can be evaluated in 5 vs. 5 plots (Gregory Criss 1986). 

In an attempt to establish the fluid and metal sources and to help constrain a genetic model, stable isotope studies (O, Pb, S) were conducted on selected occurrences. Oxygen isotope analysis of quartz vein material from eight separate occurrences yielded values of 10.9-16.0%o. Assuming equilibrium between quartz and the hydrothermal fluid, the values calculated for the mineralizing fluids, at temperatures between 300-400°C, range between 4.0 and 11.9%o. This overlaps accepted values for both magmatic and metamorphic fluids. 

Thus, separate levels of the oceanic crust are simultaneously enriched and depleted in relative to normal mantle values because of reaction with sea water at different temperatures. Muehlenbachs and Clayton (1976) and Gregory and Taylor (1981) concluded that the 0 enrichments are balanced by the depletions which acts like a buffer for the oxygen isotope composition of ocean water. 

One portion of the oxygen in clay minerals occurs as the hydroxyl ion. Hamza and Epstein (1980), Bechtel and Hoemes (1990) and Girard and Savin (1996) have attempted to separate the hydroxyl and nonhydoxyl bonded oxygen for separate isotope analysis. Techniques include thermal dehydroxylation and incomplete flu-orination, both of which indicate that hydroxyl oxygen is considerably depleted in 0 relative to nonhydroxyl oxygen. 

Fig. 3.41 Predicted (bars) and measured (crosses) oxygen isotope composition of separated minerals from Haitian weathering profiles. The ranges of predicted values were calculated assuming a temperature of 25°C and a meteoric water value of —3. %o (after Bird et al. 1992)...

Carbonates deposited in freshwater lakes exhibit a wide range in isotopic composition, depending upon the isotopic composition of the rainfall in the catchment area, its amount and seasonality, the temperature, the rate of evaporation, the relative humidity, and the biological productivity. Lake carbonates typically consist of a matrix of discrete components, such as detrital components, authigenic precipitates, neritic, and benthic organisms. The separate analysis of such components has the potential to permit investigation of the entire water column. For example, the oxygen isotopic... 

Liebscher A, Barnes J, Sharp Z (2006) Chlorine isotope vapor-liquid fractionation during experimental fluid-phase separation at 400°C/23 Mpa to 450°C/42Mpa, Chem Geol 234 340-345 Lister GS, Kelts K, Chen KZ, Yu JQ, Niessen P (1991) Lake Qinghai, China closed-basin lake levels and the oxygen isotope record for ostracoda since the latest Pleistocene. Palaeogeogr PalaeocUmatol Palaeoecol 84 141-162... 

Oxygen isotopic compositions (relative to standard mean ocean water, SMOW) of several mineral grains in three Stardust particles, each grain denoted by a separate symbol. Open circles are from a CAI comet particle. After McKeegan et al. (2006). 

As of early September, 1985, the facility is being commissioned. Carbon, nitrogen and oxygen beams from the tandem have reached the interim target locations via the bypass line, and an iodine beam has been injected into the cyclotron. First attempts to accelerate iodine in the cyclotron are imminent Some experimental equipment, including the on-line isotope separator [SCH81J, is already set up and undergoing tests with tandem beams. 

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