Uranium Determination by Remote Time-Resolved Laser-Induced Fluorescence

Abstract

Uranium measurements taken in a hostile environment are required in the nuclear fuel cycle. Current trends are leading toward development of better sensitivity and rapidity as well as remote measurements. Time-Resolved Laser-Induced Fluorescence (TRLIF) is a very selective and sensitive method that has been widely used for uranium determinations in complex matrices. This technique evolved from analysis in a cell located in a glove box to remote measurements via fiber optics in a shielded cell. The setup of Remote Time-Resolved Laser-Induced Fluorescence (RTRLIF) includes an excitation laser focused in the excitation fiber, with the fluorescence collection fibers concentrically positioned around the excitation fiber at the optrode tip, which dips into the solution; the signal is analyzed by a pulsed intensified multichannel spectrofluorimeter. This analyzer allows for the elimination of the unwanted parasital fluorescence (organic, Raman) by the placement of a gate a few microseconds after the laser pulse. Special care is taken in terms of laser focalization, fiber-optic parameters (numerical aperture, diameter, and arrangement), parasital fluorescence, time delay, and width of the gate. Results obtained with RTRLIF in terms of limits of detection (LOD ∼ 10⁻¹⁰ M) are presented and compared with the results obtained by TRLIF.