Isotope front

Bickle M. J. and Baker J. (1990) Advective-diffusive transport of isotopic fronts an example from Naxos, Greece. Earth Planet. Sci. Lett. 97, 78-93. 

Wada H., Ando T., and Suzuki M. (1998) The role of the grain boundary at chemical and isotopic fronts in marble during contact metamorphism. Contrib. Mineral. Petrol. 132, 309-320. 

The fractionation factor (a. /) is very close to 1 (0.99 to 1.01) at high temperatures for most isotopic systems of interest (i.e. A,.y < 10%o). Hence the movement of the front depends mainly on the relative abundance of the element in the mineral and the fluid phase, rather than the isotopic concentrations. Since the relative mobility of the fronts is independent of fluid velocity and porosity (if it is small), one can use the relative location of stable isotope fronts to determine the concentration ratio of these elements in fluid phase (e g. Baun artner and Rumble 1988 Gerdes et al. 1995a). The relative retardation of the and fronts recorded by the model calcite column infiltrated by a binary H2O-CO2 fluid is approximated by ... 

Bickle MJ (1992) Transport mechatusm by fluid flow in metamorphic rocks oxygen and strontirrm decoupling in the Trois Seigneurs Massif A consequence of kinetic dispersion. Am J Sci 292 289-316 Bickle JM, Baker J (1990a) Advective-dispersive transport of isotopic fronts An example from Naxos, Greece. Earth Planet Sci Lett 97 78-93... 

Bickle JM, Baker J (1990b) Migration of reaction and isotopic fronts in infiltration zones Assessments of fluid flux in metamorphic terrains. Earth Planet Sci Lett 98 1-13 Blattner P, Lassey R (1989) Stable isotope exchange fronts, Damkohler numbers, and flnid-rock ratios. ChemGeol 78 381-392... 

Skelton ADL, Valley JW, Graham CM, Bickle Ml, Falhck AE (2000) The correlation of reaction and isotope fronts and the mechanism of metamorphic flnid flow. Contrib Mineral Petrol 138 364-375 Smith RK (1972) The mineralogy and petrology of the contact metamorphic anreole atoimd the Alta stock, Utah. PhD Dissertation, University Iowa, Iowa City... 

To support them, therefore, immense activities are prompted both in pubh c private sectors with increasing importance on NDT. The particular application of radiography using Ir-192 isotopes for industrial production, construction maintenance of industries, power plants, oil and gas pipelines plants, railway, aviation systems, naval structures and vessels, etc is currently in the fore front for its reliabih ly, ease of application record keeping advantages. 

Ernest O. Lawrence, inventor of the cyclotron) This member of the 5f transition elements (actinide series) was discovered in March 1961 by A. Ghiorso, T. Sikkeland, A.E. Larsh, and R.M. Latimer. A 3-Mg californium target, consisting of a mixture of isotopes of mass number 249, 250, 251, and 252, was bombarded with either lOB or IIB. The electrically charged transmutation nuclei recoiled with an atmosphere of helium and were collected on a thin copper conveyor tape which was then moved to place collected atoms in front of a series of solid-state detectors. The isotope of element 103 produced in this way decayed by emitting an 8.6 MeV alpha particle with a half-life of 8 s. 

Racemization, however, does not alwiys accompany isotopic scrambling. In the case of 5ec-butyl 4-bromobenzenesulfonate, isotopic scrambling occurs in trifluoroethanol solution witiiout any racemization. Two mechanisms are possible. Scrambling may involve an intimate ion pair in which the sulfonate can rotate with respect to the caibocation without allowing migration to die other face of the caibocation. The alternative is a concerted mechanism, which avoids a caibocation intermediate but violates the prohibition of front-side displacement. ... 

Abundances of lUPAC (the International Union of Pure and Applied Chemistry). Their most recent recommendations are tabulated on the inside front fly sheet. From this it is clear that there is still a wide variation in the reliability of the data. The most accurately quoted value is that for fluorine which is known to better than I part in 38 million the least accurate is for boron (1 part in 1500, i.e. 7 parts in [O ). Apart from boron all values are reliable to better than 5 parts in [O and the majority arc reliable to better than I part in 10. For some elements (such as boron) the rather large uncertainty arises not because of experimental error, since the use of mass-spcctrometric measurements has yielded results of very high precision, but because the natural variation in the relative abundance of the 2 isotopes °B and "B results in a range of values of at least 0.003 about the quoted value of 10.811. By contrast, there is no known variation in isotopic abundances for elements such as selenium and osmium, but calibrated mass-spcctrometric data are not available, and the existence of 6 and 7 stable isotopes respectively for these elements makes high precision difficult to obtain they are thus prime candidates for improvement. 

Some of the important properties of the elements are given in Table 18.1. The imprecision of the atomic weights of Kr and Xe reflects the natural occurrence of several isotopes of these elements. For He, however, and to a lesser extent Ar, a single isotope predominates ( He, 99.999 863% " Ar, 99.600%) and much greater precision is possible. The natural preponderance of " Ar is indeed responsible for the well-known inversion of atomic weight order of Ar and K in the periodic table, and the position of Ar in front of K was only finally accepted when it was shown that the atomic weight of He placed it in front of Li. The second isotope of helium, He, has only been available in significant amounts since... 

Development efforts in the nuclear industry are focusing on the fuel cycle (Figure 6.12). The front end of the cycle includes mining, milling, and conversion of ore to uranium hexafluoride enrichment of the uranium-235 isotope conversion of the enriched product to uranium oxides and fabrication into reactor fuel elements. Because there is at present a moratorium on reprocessing spent fuel, the back end of the cycle consists only of management and disposal of spent fuel. 

For purposes of chemical bookkeeping, it is unnecessary to know the isotopic molar masses and isotopic distributions of the elements. All we need to know is the mass of one mole of an element containing its natural composition of isotopes. These molar masses usually are included in the periodic table, and they appear on the inside front and back covers of this textbook. 

Most Mossbauer experiments are currently performed with commercially available radioactive sources. For some applications, however, a so-called source experiment may be useful, in which the sample is labeled with the radioactive parent-isotope of the Mossbauer nucleus such as Co. The y-radiation of the radioactive sample is then analyzed by moving a single-line absorber for Doppler modulation in front of the detector. 

Decay of the nuclide itself. The conceptually simplest approach is to take a known quantity of the nuclide of interest, P, and repeatedly measure it over a sufficiently long period. The observed decrease in activity with time provides the half-life to an acceptable precision and it was this technique that was originally used to establish the concept of half-lives (Rutherford 1900). Most early attempts to assess half lives, such as that for " Th depicted on the front cover of this volume, followed this method (Rutherford and Soddy 1903). This approach may use measurement of either the activity of P, or the number of atoms of P, although the former is more commonly used. Care must be taken that the nuclide is sufficiently pure so that, for instance, no parent of P is admixed allowing continued production of P during the experiment. The technique is obviously limited to those nuclides with sufficiently short half-lives that decay can readily be measured in a realistic timeframe. In practice, the longest-lived isotopes which can be assessed in this way have half-lives of a few decades (e.g., °Pb Merritt et al. 1957). 

The most important observations about U-series isotopes in arc lavas for this chapter are (1) the widespread excess of over °Th but deficit of with respect to Pa and (2) the extreme Ra enrichments in some arc lavas. We will explore the profound implications of these for magma genesis and transport at subduction zones. The conclusions apply most convincingly to the oceanic arcs where the observations are most extreme (the volcanic fronts of Tonga, Marianas, and eastern Sunda, and one or two volcanoes in some other arcs). Whether the conclusions apply elsewhere is harder to verify but there is no convincing reason with respect to U-series data to believe that they do not. 

Ewart A, Hawkesworth CJ (1987) The Pleistoeene-Reeent Tonga-Kermadee are lavas Interpretation of new isotopic and rare earth data in terms of a depleted mantle somce model. J Petrol 28 495-530 Fumkawa F (1993a) Magmatic processes under arcs and formation of the volcanic front. J Geophys Res 98 8309-8319... 

It should be emphasized that the symmetry number ratio (s2/si) is entered as a multiplier of (s2/si)f so that the symmetry number factors which lead to no isotopic enrichment in themselves are left out. To obtain the complete isotope effect one has to multiply the above expression by symmetry number ratios so that the symmetry number ratios in front of the f expressions are removed. So the symmetry number factor in Equations 4.143 and 4.144 is given by... 

Se is concentrated in certain ore deposits, such as roll-front U complexes and Carlin-type gold deposits. Roll-front U deposits occur where U(Vl)-bearing groundwater migrates into reducing zones which precipitate both U(TV) and Se(0) or Se(-II). It may be possible to constrain Se sources and/or ore-forming processes using Se isotope variations. 

Hart S. R. (1964). The petrology and isotopic-mineral age relations of a contact zone in the Front Range, Colorado. J. Geol, 72 493-525. 

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