Time-resolved laser-induced fluorescence is a unique method for direct uranium speciation at low level in the framework of environmental studies. By varying pH and uranium concentration in the absence of carbonate ions and at fixed ionic strength, it was possible, together with free uranyl UO2 2+, to identify spectrally and temporally all the uranium-hydroxo complexes, namely, UO2 OH+, UO2 (OH)2 , UO2 (OH)3-, (UO2)2(OH)2 2+, (UO2)3(OH)5+, and (UO2)3(OH)7-.

Time-resolved laser-induced fluorescence as a unique tool for low-level uranium speciation

Advances in technologies for the measurement of uranium in diverse matrices

Time-resolved laser-induced fluorescence (TRLIF) has been used for direct uranium(VI) determination in the nuclear reprocessing medium. To take into account the different phenomena that affect the uranyl fluorescence (absorption, quenching, and complexation), a model has been defined. A spectral deconvolution procedure allows uranium speciation in nitric acid and therefore nitrate determination with good accuracy. After normalization of the fluorescence intensity, it is then possible to reach the uranium concentration. Results obtained on synthetic solutions and, above all, on reprocessing samples by the application of this model are presented and compared with results from other techniques. The limit of detection for uranium analysis in reprocessing matrices is in the submilligram per liter range, and a ratio of Pu/U as high as 105 can be directly analyzed.

Direct Uranium(VI) and Nitrate Determinations in Nuclear Reprocessing by Time-Resolved Laser-Induced Fluorescence

Results of an inter-laboratory round-robin study of the application of time-resolved emission spectroscopy (TRES) to the speciation of uranium(VI) in aqueous media are presented. The round-robin study involved 13 independent laboratories, using various instrumentation and data analysis methods. Samples were prepared based on appropriate speciation diagrams and, in general, were found to be chemically stable for at least six months. Four different types of aqueous uranyl solutions were studied: (1) acidic medium where UO22+aq is the single emitting species, (2) uranyl in the presence of fluoride ions, (3) uranyl in the presence of sulfate ions, and (4) uranyl in aqueous solutions at different pH, promoting the formation of hydrolyzed species. Results between the laboratories are compared in terms of the number of decay components, luminescence lifetimes, and spectral band positions. The successes and limitations of TRES in uranyl analysis and speciation in aqueous solutions are discussed.

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Aqueous solutions of uranium(VI) as studied by time-resolved emission spectroscopy: A round-robin test

We report the development of a whole-field fluorescence lifetime imaging (FLIM) system with high temporal resolution based on a time-gated image intensifier. The optimized temporal gate width is < 100 ps, and changes in the environment of a fluorescent phantom, causing lifetime differences less than 10 ps, have been imaged. The versatility of this FLIM system has been demonstrated by measuring both the temporal and spectral profiles of multiple fluorescent samples in a single acquisition. Initial fluorescence lifetime images suggest that this technique can provide a means of distinguishing between different tissue constituents.

Laurent Trecani

Papers

Direct and fast uranium determination in zirconium by time-resolved laser-induced fluorescence spectrometry