Radionuclide species

Nuclide Concentrations. The two nuclide concentrations chosen for the experiments, <10- M and =10" M, are so low that the ionic strength of the water is not significantly affected. Nor is it likely that the solid sorbent would be saturated with respect to the sorption capacity of any individual radionuclide species. 

Generally, a significantly increased distribution coefficient is obtained after a contact time of 6 months in comparison with 1 week (by a factor of less than five), especially for the tri-and tetravalent elements (and Ra) on granite. Evidently the diffusion of hydrolyzed products into the grains is a slow process. Radionuclide Species in Groundwater... 

Proposed radionuclide species in non-oxidizing granitic groundwater... 

In the case of solid environmental materials such as soils, sediments or indeed suspended particulates the use of selective chemical leaching methods can provide some basic information regarding the nature of the radionuclide species bound to the solid matrix. A typical sequential leaching might follow a procedure similar to that suggested for the study of trace metal binding to sediments by Gupta and Chen (1975) as shown in Fig. 13.2. 

Figure 13.2 A sequential chemical leaching procedure which may be used to investigate the binding of radionuclide species to soil or sediment matrices.

Methodological artefacts may arise for a number of reasons, most notably as a result of specific interactions of species with the filter membrane. Therefore the choice of the ultrafiltration system, the properties and influence of the membrane and the operating conditions must be carefully considered before the ultrafiltration technique is applied for the separation of different radionuclide species in environmental samples. 

Aqueous radionuclide species and other solutes can sorb to mineral surfaces by forming chemical bonds directly with the amphoteric sites or may be separated from the surface by a layer of water molecules and be bound through longer-range electrostatic interactions. In the TLM, complexes of the former type are often called inner-sphere complexes those of the latter type are called outer-sphere complexes (Davis and Kent, 1990). The TLM includes an inner plane (o-plane), an outer plane (/8-plane), and a diffuse layer that extends from the /8-plane to the bulk solution. Sorption via formation of inner-sphere complexes is often referred to chemisorption or specific... 

Some nuclei undergo radioactive decay by capturing an electron from the A or L shell of the atomic electron orbits. This results in the transformation of a proton to a neutron, the ejection of an unobservable neutrino of definite energy, and the emission of an x-ray where the electron vacancy of the or L shell is filled by an atomic electron from an outer orbit. Because the net change in the radionuclide species is from atomic number Z to Z — 1, similar to the nuclide change from positron emission, electron capture generally competes with all cases of positron beta decay. 

The mathematical relationship expressed in (8) shows that the amount of induced radioactivity, and therefore the sensitivity of measurement, is influenced by factors that are constant for a particular isotope (i.e., its activation cross section and the decay constant of the induced radionuclide species). Likewise, variable factors that are controlled by the experimenter—that is, length of bombardment time the elapsed time from end of bombardment to the time of radioactivity measurement (the decay period) sample weight and the method of measuring the radioactivity—also influence the sensitivity of the activation analysis method for a given element. 

Because naturally occurring and artificially produced radionuclides in the environment may be present in different physicochemical forms (i.e., radionuclide species) varying in size... 

The Principles of Colloid Facilitated Radionuclide Transport outlined in the first section support the conclusion that colloid facilitated radionuclide transport is a phenomenon that will probably take place only under limited system conditions. Systems that we define here as being symmetrical are probably the dominant systems under natural conditions they also are the systems for which colloid-facilitated radionuclide transport will be minimal. In addition, radionuclides that are subject to colloid-facilitated transport have a dissolved phase component that is, in many cases, negligible. Kersting et al. (1999), for example, evaluated Pu at levels of around Laboratory studies provide incontrovertible examples that colloidal materials can enhance the transport of low-solubility radionuclide species but field studies remain ambiguous because the colloids, themselves, are not traced. 

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