Eu isotopic measurements with in situ Eu/Gd/Sm separation using O-2 as a reactant gas in collision/reaction cell based MC-ICP-MS

The Nuclear Energy Division of the French Atomic Energy commission is carrying out research in the transmutation field in order to access the possibility of eliminating long-lived nuclear waste. Within this frame, many selected targets of highly enriched actinides or fission products are irradiated in the Phenix French Nuclear Reactor, and analysed before and after irradiation for their elemental and isotopic composition. Among them, the Eu-153 presents a major analytical challenge because neutronic calculation codes predict the formation of isobaric interferences of samarium and gadolinium isotopes after irradiation. An analytical method was developed by using a Multiple Collector-Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS, Isoprobe) equipped with a collision/reaction cell in order to circumvent these interferences. In this article, it is shown that direct Europium isotopic ratios measurements are possible in the presence of O-2 used as reactant gas in the cell due to the opposite behaviour of Eu and Sm/Gd towards this gas. SmO+ and GdO+ oxide ions are fully formed whereas Eu is mainly present as Eu+. The separation efficiency of the Isoprobe's collision reaction-cell was studied on both natural Eu and certified Eu-153 enriched solutions. Accuracy of the measurement was found to be within the reference value uncertainty. Reproducibility of Eu-151/Eu-153 isotopic ratio measurement were found to be lower than 0.3 parts per thousand, in the case of natural solution, and lower than 4 parts per thousand with the Eu-153 enriched solution, respectively. This study presents an original measurement method for a triple Eu/Gd/Sm isobaric interference resolution in order to measure the Eu isotopic composition with high precision and accuracy.