Triple-filament method for solid-sample lead isotope analysis

A triple-filament method for lead isotope analysis has been devised. The source consists of rhenium-ribbon sample filaments and a platinum-ribbon ionizing filament. Samples may be mounted as PbCl2, Pb(NO3)2, or Pb(OH)2; the Pb(OH)2 appears to have the best qualities. Stable lead ion signals of 6 × 10−11 amp are consistently obtained with 500-µg lead samples, whereas 20-µg samples give stable signals of 4 × 10−13 amp. The triple-filament method does not have the ionization efficiency of the single-filament PbS or PbC2O4 method, but it has much greater precision. Ten analyses of a reference sample gave 95% confidence limits (per analysis) of Pb204/Pb206 = 0.054%, Pb207/Pb206 = 0.023%, and Pb208/Pb206 = 0.071%.