HIGH-RESOLUTION SIMS ANALYSIS OF COMMON LEAD

An evaluation of the SIMS technique for precise analysis of common lead in natural materials has been undertaken. The instrument used is a new generation of high-resolution, high-transmission ion probe - the ISOLAB-120(R). Two glass standards (NBS-610 and ''Waterford'') have been characterised for their Pb-isotope composition by TIMS. Repeated SIMS analyses of these materials have failed to reveal any resolvable mass discrimination of Pb isotopes. The mass discrimination is shown to be < 0.2% amu-1 in all cases. Comparison of SIMS Pb analyses of natural ferromanganese samples with TIMS Pb-isotope analyses on adjacent portions are in good agreement and support the conclusion that mass discrimination is minimal. The basic performance characteristics of the instrument operated at high mass-resolving power are detailed in terms of transmission, extraction efficiency, Pb+ ion yield from different materials and repeatability of measurements. The precision and accuracy of common Pb isotope ratio measurement by SIMS approaches that of TIMS to the point where application to palaeo-oceanographic problems for example become entirely feasible.