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The lifetimes of the lowest 3 P 1 states of Ba and Ra were determined to be 1345± 14 ns and 422± 20 ns, respectively, by measuring the exponential decay of fluorescence after illuminating a thermal atomic beam with pulses of laser light. In addition, the 1 S 0 ͑F =1/2͒-3 P 1 ͑F =3/2͒ transition frequency in 225 Ra was measured to be 13 999.269± 0.001 cm −1 by referencing a nearby I 2 transition.

Actinides / Lanthanides / TALSPEAK / NPEX / Separation / Pu / NpSummary. Bench-scale studies to determine the extraction behavior of Pu, Np, Am and lanthanides with the organophosphorus extractants TBP, CMPO and HDEHP have been carried out. Based on the results obtained using actual spent nuclear fuel solutions, enhancements to the NPEX, TRUEX and TAL-SPEAK processes have been successful. In NPEX, > 99.94% of both Np and Pu were separated from the fission products. In TRUEX, essentially complete recovery of the actinides (An) and the lanthanides (Ln) was achieved. In TALSPEAK, the complete separation of Pu, Np and Am from the lanthanides was demonstrated several times under various process conditions. The recovery of transuranics (TRU), including Am and Cm, is nearly 100% (below detection limit in the Ln stream), while the total recovery of Ln in the product stream exceeded 99.97%.

High-sensitivity methods for detection and speciation of complexed transuranium ions in synthetic basalt groundwater, and simplified analogs, are being developed which exploit advances in pulsed laser technology. The first demonstration of high sensitivity detection of a transuranium ion at temperatures significantly above ambient is reported using laser photoacoustic spectroscopy (LPAS). The existence of enhanced LPAS signal amplitudes with increasing temperature in aqueous solution is confirmed in LPAS spectra recorded at 30°C, 60°C and 90°C using micromolar concentrations of Am 3+ . A detection sensitivity of 8.5 parts per trillion (weight basis) of 144 Cm 3 + in a synthetic basalt groundwater at 22°C has been achieved using laser-induced fluorescence spectroscopy (LIF). This corresponds to 1 X 10* Cm 3 + ions in the laser beam. The detailed spectroscopic information obtained by this method points to the existence of previously unobserved Cm 3 + species. A brief assessment of the applicability and sensitivity of LPAS and LIF methods for speciating transuranium ions in near-neutral pH aqueous solution, such as the groundwater expected in a basalt nuclear waste repository, is presented.

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