High-Resolution Inductively Coupled Plasma Optical Emission Spectrometry For U-234/Pu-238 Age Dating Of Plutonium Materials And Comparison To Sector Field Inductively Coupled Plasma Mass Spectrometry

Employing a commercial high-resolution inductively coupled plasma optical emission spectrometry (HR-ICP-OES) instrument, an innovative analytical procedure for the accurate determination of the production age of various Pu materials (Pu powder, cardiac pacemaker battery, Cm-242 heat source, etc.) was developed and validated. This undertaking was based on the fact that the a decay of Pu-238 present in the investigated samples produced U-234 and both mother and daughter could be identified unequivocally using HR-ICP-OES. Benefiting from the high spectral resolution of the instrument (<5 pm) and the isotope shift of the emission lines of both nuclides, U-234 and Pu-238 were selectively and directly determined in the dissolved samples, i.e., without a chemical separation of the two analytes from each other. Exact emission wavelengths as well as emission spectra of U-234 centered around lambda = 411.590 nm and lambda = 424.408 nm are reported here for the first time. Emission spectra of the isotopic standard reference material IRMM-199, comprising about one-third each of U-233, U-238, and U-238, confirmed the presence of U-234 in the investigated samples. For the assessment of the U-234/Pu-238 amount ratio, the emission signals of U-234 and Pu-238 were quantified at lambda = 424.408 nm and lambda = 402.148 nm, respectively. The age of the investigated samples (range: 26.7-44.4 years) was subsequently calculated using the U-234/Pu-238 chronometer. HR-ICP-OES results were crossed-validated through sector field inductively coupled plasma mass spectrometry (SF-ICPMS) analysis of the U-234/Pu-238 amount ratio of all samples applying isotope dilution combined with chromatographic separation of U and Pu. Available information on the assumed ages of the analyzed samples was consistent with the ages obtained via the HR-ICP-OES approach. Being based on a different physical detection principle, HR-ICP-OES provides an alternative strategy to the well-established mass spectrometric approach and thus effectively adds to the quality assurance of U-234/Pu-238 age dates.