Development and Application of Methods for the Assay of Neptunium in Environmental Matrices

Hursthouse, Andrew Stefan (1990) Development and Application of Methods for the Assay of Neptunium in Environmental Matrices. PhD thesis, University of Glasgow.

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Inductively coupled plasma mass-spectrometry (ICP-MS) and neutron activation analysis (NAA) techniques have been investigated as rapid, alternative methods for the analysis of 237 Np and other long-lived actinides in environmental matrices. By comparison to the more routine a-spectrometric method, equivalent, if not improved, detection limits for ICP-MS and NAA have been found. Radiochemical separation and pre-concentration are required for all the methods studied. In this work, anion exchange and TTA solvent extraction of Np IV from hydrochloric acid media were used to separate Np from potential interferences from the naturally occurring nuclides of uranium. The degree of interference was found to vary for each approach and was quite severe in the case of NAA. Analysis by ICP-MS tolerates a lower degree of chemical purification and results in a significant increase in sample throughput. The rapid, mass-scanning facilities of the instrument have allowed multiactinide determination on single samples and have provided important additional information concerning plutonium nuclides in environmental samples. In the absence of suitable certified reference materials, the accuracy and precision of the ICP-MS technique were determined by a series of laboratory intercomparison and replicate analyses. On this basis, the reported measurements of 237Np and plutonium nuclides were considered valid. The ICP-MS method developed here has been applied to the routine analysis of 237Np and plutonium nuclides in samples of soils and sediments from W. Cumbria, known to be contaminated by discharges from the BNFL fuel re-processing plant at Sellafield. Concentrations ranging from 3.16 to 0.004 Bq kg-1 237Np have been measured with excellent precision. Typically, an exponential decrease of 237Np activity with depth has been found in a number of soil profiles. The pattern is the same as that found for other anthropogenic nuclides in the profiles but, when the effect of profile density variation is considered, it appears that a component of the neptunium is present in a more mobile form and is responsible for a degree of smearing of its distribution down the soil profile. During the transfer of Sellafield-derived 237Np from the BNFL, through the marine environment to a number of terrestrial sampling locations in W. Cumbria, the activity ratios of 237Np to 239,240Pu, 241Am and 137Cs change in a manner which implies that there is a loss of neptunium from the solid phase. Detailed studies of the chemical association of neptunium in samples of silt and surface soil show that, compared to the other transuranic nuclides studied, a significant proportion of the element is associated with the more sensitive phases the exchangeable and adsorbed components, including carbonate. The organic matter and residual phases are nevertheless found to be significant and merit further study.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Nuclear physics and radiation, Nuclear chemistry, Analytical chemistry
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-78095
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:40
Last Modified: 30 Jan 2020 15:40

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