Development of an in-situ monitoring tool for Actinide ions

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HypothesesIn aqueous solutions, actinides such as U, Np and Pu are encountered as ions which absorb intensely in the ultraviolet, visible and/or near infrared region of the electromagnetic spectrum. This indicates that illumination will result in the photoexcitation of each of those ions by promotion of an electron which may be captured by co-localised electrode either directly (photophysical-electrochemical mechanism) or indirectly via the use of an electron scavenger that effectively acts to extend the lifetime of the photoexcited species (photophysical-chemical-electrochemical mechanism). The MORE's design is built around an optical fibre light guide, which enables it to deliver monochromated light to the interrogation volume where the gold ring electrode surrounding the light guide is ideally located to electrochemically detect the often short-lived photoexcited species or the product of its decay or quenching. The fine-tuning capabilities afforded by (i) monochromated light and (ii) the electrode's working potential, allow to identify analytes based on their photophysical and electrochemical properties. The MORE has been shown capable of detecting small amounts (down to 200 nmol dm-3) of photo-electroactive analytes in solution. Crucially, it was found that the amplitude of the photocurrent is dependent on the wavelength of illumination and closely matches the absorption spectrum for the analyte. Thus, it can be used to interrogate the individual concentrations of analytes in mixtures whose spectroscopic properties are sufficiently distinct. Aims The main aim of this project is to develop a methodology to fully characterise aqueous solutions containing a range of target analytes including U, Pu and Np using the Micro-Optical Ring Electrode.Supervisor: Dr Fabrice Andrieux