Radionuclide species plutonium

The successive chemical extractions are designed to indicate the type of component phase to which the trace component is bound and from this the nature of the bound species may theoretically be inferred. But as Cremers and Henrion (1985) have pointed out, the whole basis of this type of approach is controversial and the literature contains many examples of conflicting conclusions regarding the relative contribution of the various phases. For example, in some cases plutonium and americium are reported to be solely associated with hydrous oxides (Edgington et al., 1976 Aston and Stanners, 1981) whilst, in others, these radionuclides are claimed to be fairly uniformly distributed throughout the various phase components of what appear to be similar sediments (Hetherington, 1978). 

A variety of methods have been used to characterize the solubility-limiting radionuclide solids and the nature of sorbed species at the solid/water interface in experimental studies. Electron microscopy and standard X-ray diffraction techniques can be used to identify some of the solids from precipitation experiments. X-ray absorption spectroscopy (XAS) can be used to obtain structural information on solids and is particularly useful for investigating noncrystalline and polymeric actinide compounds that cannot be characterized by X-ray diffraction analysis (Silva and Nitsche, 1995). X-ray absorption near edge spectroscopy (XANES) can provide information about the oxidation state and local structure of actinides in solution, solids, or at the solution/ solid interface. For example, Bertsch et al. (1994) used this technique to investigate uranium speciation in soils and sediments at uranium processing facilities. Many of the surface spectroscopic techniques have been reviewed recently by Bertsch and Hunter (2001) and Brown et al. (1999). Specihc recent applications of the spectroscopic techniques to radionuclides are described by Runde et al. (2002b). Rai and co-workers have carried out a number of experimental studies of the solubility and speciation of plutonium, neptunium, americium, and uranium that illustrate combinations of various solution and spectroscopic techniques (Rai et al, 1980, 1997, 1998 Felmy et al, 1989, 1990 Xia et al., 2001). 

Analysis of herbage (of forage) has sometimes been used to detect and identify radionuclides deposited from the atmosphere (Jackson et al., 1981). However, the problem arises that when the deposition rate is low, large areas of vegetation need to be sampled for detection. In the case of plutonium, an alternative is to collect the faeces of grazing animals such as cows, sheep and rabbits. Plutonium is very poorly absorbed by the mammalian gut and so virtually all that is ingested by an animal will appear in its faeces. Also, if the species selected obtains its food entirely by grazing, then the isotopic ratio Pu will be the same in the faeces as deposited on the... 

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