Transuranic isotope concentrations

Hydrological models that treat fluid behavior in sedimentary environments that lie under some kilometers of overburden are likely to require much greater time spans than is customary in studying near-surface processes. The longer-lived isotopes of transuranic elements and their daughters present in buried radioactive waste will persist for several million years (Bredehoeft et al., 1978). An example of a substance that needs, in principle, to be retained indefinitely because of the strict limits set upon its allowable concentration in drinking water is nitrate, an anion that is unfortunately not adsorbed effectively by clays and other common subsurface minerals. 

An outstanding feature of inorganic mass spectrometry is its determination of precise and accurate isotopic abundances and isotope ratios. Isotopes of the same element (of the same number of protons or atomic number of element, Z) are, by definition, nuclides with different mass m and mass number A (A = Z + N) due to the different number of neutrons (N) in the nucleus. Isotope analyses are of special interest for characterizing the composition of samples with respect to stable and unstable isotopes in quite different concentration ranges - from the analysis of matrix elements down to the trace and ultratrace concentration level.1-9 Of 1700 isotopes, nearly 16 % (264 isotopes) are stable. The chemical elements Tc, Pm, Th, U and the transuranic elements do not possess stable isotopes. 

In principle, the applications of ICP-MS resemble those listed for OES. This technique however is required for samples containing sub-part per billion concentrations of elements. Quantitative information of nonmetals such as P, S, I, B, Br can be obtained. Since atomic mass spectra are much simpler and easier to interpret compared to optical emission spectra, ICP-MS affords superior resolution in the determination of rare earth elements. It is widely used for the control of high-purity materials in semiconductor and electronics industries. The applications also cover the analysis of clinical samples, the use of stable isotopes for metabolic studies, and the determination of radioactive and transuranic elements. In addition to outstanding analytical features for one or a few elements, this technique provides quantitative information on more than 70 elements present from low part-per-trillion to part-per-million concentration range in a single run and within less than 3 min (after sample preparation and calibration). Comprehensive reviews on ICP-MS applications in total element determinations are available. " ... 

Weapons-grade plutonium, dispersed at military accidents such as Thule in 1968 or as non-fissioned weapon particles after detonation of a Pu-bomb can be characterized by high Pu content relative to the other Pu-isotopes, while accidentally dispersed Pu from the previously widely used nuclear-powered satellites are characterized by high Pu content." The ratio of americium-241 to plutonium isotopes (as " Am is formed by the decay of Pu) is proportional to the initial " Pu concentration, thus it can also be used as an indicator to assess the origin of contamination. However, in most cases, as several sources may contribute to the transuranics content in environmental samples, mixing models applying several isotope ratios are required to assess the origin of possible contamination sources. 

These data are much lower (by several orders of magnitude), than reported for DU from an unfired CHARM-3 penetrator [34] and indicates that there may be substantial variation in the concentrations of transuranic elements, fission products, and non-natural uranium isotopes in batches of DU over time. Reported data on measured 238pu/239,24opu activity ratio, at 0.036 0.002, is typical of low bum-up plutonium and would confirm that recycled uranium had been used for the production of weapons-grade plutonium [101]. 

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