High accuracy measurements of Mo isotopes by MC-ICPMS with in situ Mo/Zr separation using N2O in a collision reaction cell

In the research field concerning the nuclear transmutation of long-lived radionuclides, numerous isotopically enriched elements have been irradiated in the Phenix French reactor in order to determine basic neutronic data. The precise and accurate measurement of isotopic composition of these elements after irradiation is of prime interest. Among these elements, the Mo-95 target presents an interesting analytical challenge as the irradiation generates, among others, the interfering isotopes Mo-92 and Zr-92. A method using multiple collector inductively coupled plasma mass spectrometry (MC-ICPMS) has been developed for the precise measurement of Mo isotope composition in natural Mo and Mo-95 enriched samples solutions in the presence of Zr isobaric interferences. The Mo/Zr separation was performed in situ by injecting N2O as a reaction gas in the collision-reaction cell of the instrument. The reason why a selective chemical reaction of Zr+ with N2O forms mainly ZrO2+ product whereas Mo is not reactive, is explained. This technique leads to an efficient separation of Mo and Zr, reflected by the similar accuracy and uncertainty obtained for natural and isotopically enriched Mo isotope composition with and without Zr addition. This study demonstrates the capability of the collision reaction cell of the MC-ICPMS to separate efficiently Mo and Zr, instead of using chemical separation techniques, and to produce precise and reproducible Mo isotopic data.