Isotope tracers

The amounts of the standard isotopic species and the tracer isotopic species are represented by X and X for the sample and the reference material. The reference substance is chosen arbitrarily, but is a substance that is homogeneous, available in reasonably large amounts, and measurable using standard analytical techniques for measuring isotopes (generally mass spectrometry). For instance, a sample of ocean water known as Standard Mean Ocean Water (SMOW) is used as a reference for and 0. Calcium carbonate from the Peedee sedimentary formation in North Carolina, USA (PDB) is used for C. More information about using carbon isotopes is presented in Chapter 11. 

Positron emission tomography (PET) A medical imaging technique that helps physicians locate tumors and other growths in the body. A radioactive tracer isotope which emits a positron is incorporated into a metaholically active molecule. A scanner locates the tissues where the radioactive substance winds up. 

Irvine, James Colquhoun, obituary of, VIII, xi-xvii Isotopic tracers. See Tracers, isotopic. 

An alternative approach uses tracers, isotopically enriched materials, which are added to the system studied. Labeled compounds are available with the heavy isotope enriched to a level of 99 atom%. These are more difficult to produce than radioisotopes, making them relatively expensive. Materials labeled with stable isotopes are non-radioactive and pose no hazard to human health or the environment (Barrie Prosser, 2000). 

Exploration geochemistry, geochronology, and tracer isotopic data of copper mineralisation in dolomitic rocks, Dos Parecis Basin, Rondonia,... 

The lead isotope ratios indicate an upper cmstal source for the lead and are consistent with mineralization at 800 Ma. Tracer isotopes in carbonates and chalcocite concentrates indicate that an external fluid altered the dolomitic unit changing its isotopic composition as well as deposited copper mineralisation. 

X 10 yr) and ends with stable ° Pb, after emission of eight alpha (a) and six beta (jS) particles. The thorium decay series begins with Th (ti/2 = 1.41 X 10 °yr) and ends with stable ° Pb, after emission of six alpha and four beta particles. Two isotopes of radium and Th are important tracer isotopes in the thorium decay chain. The actinium decay series begins with (ti/2 = 7.04 X 10 yr) and ends with stable Pb after emission of seven alpha and four beta particles. The actinium decay series includes important isotopes of actinium and protactinium. These primordial radionuclides, as products of continental weathering, enter the ocean primarily by the discharge of rivers. However, as we shall see, there are notable exceptions to this generality. 

During self-diffusion in a pure material, whether a gas, liquid, or solid, the components diffuse in a chemically homogeneous medium. The diffusion can be measured using radioactive tracer isotopes or marker atoms that have chemistry identical to that of their stable isotope. The tracer concentration is measured and the tracer diffusivity (self-diffusivity) is inferred from the evolution of the concentration profile. 

When solute atoms rather than tracer isotope atoms diffuse in the B regime, further analysis is necessary. Solute atoms may be expected to segregate in the... 

Fick s first law, in the form given by Equation 5.12, allows us to define the tracer- and the self-diffusion coefficients. Diffusion of a tracer isotope is the case when a diffusing atom, which is marked by their radioactivity of by their isotopic mass (see Figure 5.1) [7], is introduced in an extremely dilute concentration in an otherwise homogeneous crystal with no driving force [4], In this case, the tracer gradient of concentration will give rise to a net flow of tracer atoms. Consequently,... 

Emphasis was therefore put on analytical procedures able to determine many elements in parallel and/or requiring almost no previous separation. procedures preferred were X-ray fluorescence using a Am source and Si(Li)-detector, atomic absorption spectrophotometry, gamma spectrometry using tracer isotopes and Ge(Li)-detector and acid-base titrations with recording of the pH-volume derivative. Table 2 summarises the use of these methods for the different elements, and it also gives a rough indication of interferences, sensitivity and accuracy obtained. 

Tracer techniques, for example, are used to obtain very small but representative and measurable samples of highly radioactive spent fuel solutions. One millilitre of the solution is then spiked with a known amount of uranium and plutonium tracer isotopes. A few microlitres of the spiked solution are dried and shipped to SAL. One to fifty nanograms of uranium or plutonium extracted from this tiny sample are sufficient for a complete analysis representing the composition of half a tonne of irradiated fuel with an accuracy of 0.3 to 0.5%. 

Werner E, Roth P, Heinrichs U, Giussani A, Cantone MC, ZUker TH et al. Internal biokinetic behaviour of molybdenum in humans studied with stable isotopes as tracers. Isotopes Environ Health Stud 2000 36 123-32. 

Analysis of the isotope distribution in target compounds can be, and frequently been, limited to measuring bulk specific activity (in the case of radioisotopes) or the overall abundance (in the case of stable isotopes) of the tracer isotope. Alternatively, the topological distribution of the isotope label can be narrowed down by chemical degradation in the case of radioactive tracers. In case of stable isotopes, the topology of isotope distribution in the target molecule can be assessed in considerable detail by NMR spectrometry, mass spectrometry, or a combination of these methods. 

If the sample has less of the tracer isotopic species than the reference material, <5 will be negative. Since many of the tracer species are heavier than the reference species ( C, C vs C or S vs S), this has led to use of the term "light" for substances having less of a tracer species than the standard species. 

Infrared spectra, of carbohydrates, 12, 13-33 Infrared spectroscopy, and carbohydrate chemistry, 19, 23-49 Irvine, James Colquhoun, obituary of, 8, xi-xvii Isotopic tracers. See Tracers, isotopic. 

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