Potential of high resolution ICP-OES for elemental and isotopic analysis of americium

Abstract

The potential of the eleven most sensitive emission wavelengths of americium (Am) for prospective isotopic and elemental analysis was investigated in detail using a commercial high resolution ICP-OES spectrometer. Calibration of the instrumental response was carried out through stepwise dilution of a 241Am stock solution (1 550 mg/kg) that was prepared in-house via chemical separation of the element from a concentrated plutonium (Pu) solution (115 g/L). Sector field ICP-MS and α- and γ-spectrometry served to characterise extensively the employed Am and Pu solutions for their actual concentration, potential impurities and isotopic purity. Hyperfine splitting of relatively broad peaks (~ 10 pm) or multiplets, i.e. multiple peaks, was observed for most tested Am ICP-OES emission signals with 241Am and 243Am revealing identical signal patterns. The isotopic shift between 241Am and 243Am was generally small with a maximum difference of only ~ 3.7 pm found at λ = 450.945 nm and λ = 469.970 nm, respectively. As a consequence, the extraction of Am isotopic information from the ICP-emission spectra was limited. The use of a high efficiency sample introduction system helped to lower detection limits (LOD) for Am up to two orders of magnitude compared to previous values. While the emission wavelength λ = 283.226 nm provided the lowest LOD of 0.07 μg/kg, distinct spectral interferences originating from thorium (Th) (λ = 283.231 nm), would hamper the reliable determination of Am in Th-based nuclear fuels. A detailed interference study highlights the potential and drawback of each investigated emission wavelength for ICP-OES analysis of Am with special emphasis on nuclear fuel samples containing substantial amounts of Th, Pu and U.