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|Title: ||Improving the utility of LA-ICP-MS for isotope ratio analyses of single particles with application to uranium oxide|
|Authors: ||Craig, Grant|
|Keywords: ||Laser ablation|
|Issue Date: ||2016|
|Publisher: ||© Grant Craig|
|Abstract: ||The determination of the isotopic composition of single uranium oxide particles, size 0.3-2 μm, for
nuclear safeguards is current performed by either thermal ionisation mass spectrometry (TIMS) or
Secondary Ion Mass Spectrometry (SIMS). Laser Ablation-Inductively Coupled Plasma-Mass
Spectrometry (LA-ICP-MS), a well-established analytical technique for determining the isotopic
composition of solid materials, has the potential to be another method by which single uranium
oxide particles can be analysed, complementing established protocol, but requires optimisation.
In this study the ability of LA-ICP-MS to determine the isotopic composition, principally 234U/238U,
235U/238U and 236U/238U, of glass reference materials and sub-micron uranium oxide particles is
investigated. To achieve the best detection efficiency a prototype high-speed ablation cell and
injector design, designed previously at Loughborough University, was coupled to a high efficiency
multi collector (MC-) ICP-MS. As a result an increase in signal-to-noise ratio and a measured
detection efficiency of 5-7% was achieved for a LA-MC-ICP-MS system. The capability of the LA-MC-ICP-MS
system, for the determination of the uranium isotopic composition of single particles was
compared to a more established low-volume ablation cell. A source of additional uncertainty, blind
time arising from incompatibilities with the mixed detector array of the MC-ICP-MS was identified.
The impact of the additional uncertainty on isotope ratio analysis was modeled and a method
developed to filter out affected data.
LA-ICP-MS and LA-MC-ICP-MS were used to successfully determine the uranium isotopic
compositions of sub-micron uranium oxide particles, of a known certified composition. A sample
planchet containing particles of two distinct isotopic compositions was resolved.
The utility of three data evaluation strategies to determine the isotopic composition of single
uranium oxide particles was investigated. The necessity and advantages of calculating isotope ratios
using the geometric mean is demonstrated, which has application for isotope ratio analysis
performed on all forms of mass spectrometry.
A novel approach to prepare particulate samples for laser ablation analysis, cytocentrifugation, is
described. By using as the solvent, a mixture of nail polish and acetone, dispersed particles are held
in a strong film layer thin enough to allow embedded particles to be imaged by SEM-EDX. A sample
of uranium oxide particles in an environmental matrix prepared using cytocentrifugation is analysed
by LA-MC-ICP-MS and their isotopic composition resolved.|
|Description: ||A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.|
|Appears in Collections:||PhD Theses (Chemistry)|
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