STUDIES ON THE EVAPORATION AND IONIZATION BEHAVIOR OF URANIUM AND PLUTONIUM IN THERMAL IONIZATION MASS-SPECTROMETRY

Studies are reported on the evaporation and ionisation behaviour of ur anium (U) and plutonium (Pu) under conditions of their simultaneous ma ss spectrometric analyses using a double rhenium filament assembly, a multicollector Faraday cup detector system and a synthetic mixture of SRM-200-U and SRM-947-Pu with the U/Pu ratio as 10. The U+ and UO+ ion s start appearing at an evaporation filament temperature lower than th at for appearance of Pu+. However, the ion current of Pu+ is 5-10 time s greater than that of U+. The coexistence of oxides of Pu and U on th e evaporation filament appears to enhance the stability of UO+. Two di fferent approaches are compared to account for Pu-238 isobaric interfe rence at U-238 during simultaneous isotopic analyses of U and Pu from the same filament loading. The K factor values for U and Pu during the ir simultaneous mass spectrometric analyses are lower compared with th ose observed previously when U and Pu are analysed from separate filam ent loadings with chemically pure fractions of each.