Laser-induced Photoacoustic Spectroscopy for the Chemical Speciation of Pu(VI)

Speciation of actinide in natural aquatic system is of great interest for the safety assessment of a nuclear waste disposal in deep geological system [1]. Actinide ions form complicate complexes with various ligands such as OH, CO3, and humic substances in groundwater. These complexes can enhance or reduce the migration of actinide elements. The direct speciation of these complexes in groundwater requires a highly sensitive and selective method which is capable to determine trace amount of actinides and to identify the different complexes without separation. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is a very suitable method for trace analysis (down to 10 M) of some actinides such as U(VI), Cm(III) and Am(III). For chemical speciation of actinides complexes which show no fluorescence feature such as U(IV), Pu(III-VI) and Np(IV/V) complexes, laser-induced photoacoustic spectroscopy (LPAS) was reported a possible sensitive spectroscopic technique (down to 10 M) [2-3]. In this work, a LPAS system using a tunable laser which can be tuned from 410 to 2400 nm was installed to investigate various actinide complexes. Optical parametric oscillator (OPO) technique makes it convenient to investigate various actinides absorbed in visible and near-IR wavelength ranges. In this work, LPAS was applied for the speciation of U(IV) and Pu(VI) ions in visible and near-IR wavelength range. Absorption of water in aqueous samples has influence on LPAS spectra of target ions over 600 nm in wavelength. Speciation sensitivity of mM concentration ranges for Pu(VI) were achieved.