Nuclides, heavy metal

Classical speciation of radionuclides is described in Chapter 13. Methodology for single and sequential extraction of soil to assess radionuclide availability to plants is similar to that used for heavy metals, and has recently been reviewed (Kennedy et al., 1997). Therefore, only recent applications of sequential extraction to speci-ate both natural and anthropogenic nuclides are discussed below. 

Tsunogai, S., Nozaki, Y. and Minagawa, M. Behavior of heavy metals and particulate matters in sea water expected from that of the radioactive nuclides. J. Oceanogr. Soc. Japan... 

The specific problems discussed in this book require the use of fundamental concepts and equations from various fields like kinetic theory of gases, kinetics of chemical reactions, thermodynamics and mass transfer. This chapter presents some basic relationships relevant to these problems. From the very beginning, the studies of gas-phase radiochemistry of heavy metallic elements have been largely motivated by the quest for new man-made chemical elements. It necessitated experimentation with very short-lived nuclides on one-atom-at-a-time basis. We will pay much attention to this direction of research. Accordingly, we will consider microscopic pictures (at the atomic and molecular level) of the processes underlying the experimental methods and concrete techniques, and follow individual histories of the molecules. 

There are several lines of evidence that nucleosynthesis takes place in stars. The compositions of the outer envelopes of evolved low- and intermediate-mass stars show enhancements of the products of nuclear reactions (hydrogen and helium burning and s-process nucleosynthesis, as defined below). The ejecta of supemovae (stellar explosions) are highly enriched in short-lived radioactive nuclides that can only have been produced either just before or during the explosion. At the other extreme, low-mass stars in globular clusters, which apparently formed shortly after the universe formed, are deficient in metals (elements heavier than hydrogen and helium) because they formed before heavy elements were synthesized. 

The investigation of isotopic separations in systems with cyclic polyethers has been carried out up to now for the elements lithium, calcium and sodium, in particular. Among these elements, the enrichment of Li is of essential importance for the production of tritium and that of the heavy calcium isotopes for medical labeling experiments. An enrichment aspect does not exist for the monoisotopic element sodium. Investigations with the radioactive nuclides Na and Na are obviously of interest for fundamental investigations because these isotopes can be easily and precisely measured by their y-activity. Except for uranium, most of the investigations on other chemical exchange systems with metal ions are also based on measurements with lithium and calcium, respectively. 

Over the years, the development of models for the production of these three types of nuclides has largely relied on the bulk Solar System abundances, and on the decomposition of these abundances into the contributions from the s-, r- and p-processes. These data have been complemented with a myriad of spectroscopic observations from which heavy element abundances have been derived in a large sample of stars in different galactic locations and with different metallicities. 

Fig. 18. Heavy-element abundance patterns for three heavy-element-rich metal-poor stars, the [Eu/Fe] ratios of which are included in Fig. 16. The solid lines represent a scaled SoS r-nuclide distribution. Inverted triangles indicate upper limits...

Figure 33 provides a schematic view of a typical SNII p-process flow. Its distinguishing feature is that it evolves from heavy to light nuclides as a result of the dominant action of photodisintegrations. Figure 34 displays p-nuclide yields in the form of normalized overproduction factors computed for a variety of SNII explosions of solar-metallicity stars (results for each star... 

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