Argonne Chemistry Research Areas

Heavy Element Photophysics and Photochemistry

High-Sensitivity, High-Selectivity Determination of Curium in Water via Laser-Induced Fluorescence (LIF)

Laser-induced fluorescence is one of several laser-based methods that we use in our studies on the photophysics and photochemistry of lanthanide and actinide ions. Our work is providing scientific knowledge that is essential for assessing new processes, techniques, methods, and approaches that seek to address nuclear fuel cycle issues within the U. S. Department of Energy. We have shown that laser-induced fluorescence (LIF) is the highest sensitivity means of detecting curium in water. In addition, this method achieves a high degree of selectivity. Curium is a man-made heavy element that belongs to the actinide series of chemical elements. It is produced in nuclear reactors and is the predominant source of alpha particles in recently discharged nuclear reactor fuel. Laser-induced fluorescence from curium ions in a dilute acid solution in a rectangular sample cell is depicted in the animated graphic below.

Before laser excitation, the liquid water solution in the sample tube contains curium ions in their ground electronic state. The liquid is colorless because the ions absorb very little visible light. When a blue laser pulse passes through the cell, some of the curium ions absorb the laser light and thereby become electronically excited. These excited ions lose a small amount of energy in relaxing to their lowest lying excited electronic state.

When excited curium ions lose energy by emitting the characteristic reddish-orange light seen in the graphic, they return to their ground electronic state and become available to absorb additional laser photons from the next laser pulse. Excited curium ions also lose energy to surrounding water molecules. The net result is that reddish-orange light diminishes to about half of its initial intensity in 44 millionths of a second after a blue laser pulse, whose duration is only a few billionths of a second, has passed through the curium-containing liquid. Due to these differing time scales, a nonlinear time scale was used to construct the graphic.

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