ISOTOPE RATIO MEASUREMENTS IN STRONTIUM USING 2-PHOTON 2-COLOR RESONANCE IONIZATION MASS-SPECTROMETRY

A simple two-photon two-colour excitation scheme has been investigated , using a UV Ar+-ion laser pumped-dye laser system, for isotopic analy sis of Sr by continuous wave laser resonance ionization mass spectrome try (RIMS). Strontium ion yield measurements were made in an ion micro probe with multi-collection facility, employing both thermal evaporati on and solid target sputtering by primary ion beams of O+, Ar+, and Xe +, for producing neutral Sr atoms. These measurements have displayed a consistent depletion of the odd Sr-87:Sr-86 isotope ratio from the st andard value by as much as 10% (or 100 parts per thousand) and the dep endence of this observed even-odd mass isotopic selectivity of the ion ization process on the resonant dye laser power has been examined. The elemental selectivity of the ionization scheme for Sr has also been d emonstrated to be in excess of 10(6) over isobarically interfering Rb. The ionization yields obtained with both thermal evaporation and prim ary ion beam sputtering are compared with the results of simple mathem atical analyses of the resonance ionization process and possible reaso ns for the quantitative differences observed between the measured and the predicted results are suggested and discussed.