Determination of uranium, thorium, plutonium, americium, and curium ultratraces by photon electron rejecting alpha liquid scintillation

The determination of activities of thorium, uranium, plutonium, americium, and curium at very low levels has been performed by a new a liquid scintillation system (PERALS, name registered to Ordela, Inc.). The limit of detection has been determined for these nuclides with calculated values often lower than those obtained by other methods, like ICPMS/HP/Mistral, time-resolved laser-induced spectrofluorometry, and alpha spectrometry. All the results obtained show that the PERALS system is a promising method for the determination of these activities at very low levels. However, its energy resolution is inferior in comparison to that obtained by a spectrometry. For this reason, we have developed a process for separation of the five actinides as quickly and easily as possible. For each actinide, the conditions required to obtain optimal extraction yields and a complete separation have been determined. It is possible to perform the separation in only six extraction steps and to measure activities as low as a few millibecquerels per liter independently. This process has been applied with success to French granitic mineral or doped water and to complex media (biological samples like urines). In this latter case, the extraction recoveries are not quantitative, and it is necessary to determine the recovery yields by labeling with spikes like Th-230, U-232, Pu-236, Cm-248, and Gd-148.