Our laboratory routinely performs high-precision analyses on a variety of sample types in the following isotopic systems:
These analyses are carried out using three multi-collector thermal ionization mass spectrometers (TIMS), including a VG Sector 54, a GV Instruments Isoprobe-T, and a state-of-the-art Isotopx X62.
Accessory Mineral Uranium-Lead
Analyses of accessory minerals, primarly zircon, are performed using mixed 205Pb-233U-235U or 202Pb-205Pb-233U-235U isotopic tracers, with total procedural blanks that are routinely 0.4 picograms or less for lead, and less than 0.1 picograms for U. Using single collector ion counting with peak-jumping, we achieve high-precision analyses of samples with as little as a few picograms of radiogenic Pb; at present, our minimum sample size is blank-limited.
Samarium-Neodymium
Neodymium is routinely analyzed as metal in dynamic mode with external reproducibility of isotope ratios over 15 years better than 20 ppm (2σ). La Jolla Nd analyses over the same period yield 143Nd/144Nd = 0.511854 ± 0.000009 (2σ) for 144Nd = 1.5×10-11 amp analyses. Samarium is typically analyzed in static multicollector mode with precision better than 0.01% (2σ).
Rubidium-Strontium
Routine Sr isotopic analyses are done by dynamic multi-collection on the Isoprobe T. Sr is loaded onto Re filaments with H3PO4 and TaCl5 activator and produces a stable beam for several hours, even for small samples. The external reproducibility of our 87Sr/86Sr analyses is better than 25 ppm (2σ) over the past 15 years. The 87Sr/86Sr of NBS-987 over that time period averages 0.710238 ± 0.000011 (2σ) for analyses with 88Sr = 3×10-11 amps. Total procedure blanks for Sr are less than 40 pg. Rb analyses are done in static mode.
Common Pb
Common Pb analyses are done in static multicollector mode, or with the Daly detector in peak-jumping mode. In static multicollector mode, samples as small as a few nanograms can easily be analyzed; for smaller samples, the Daly detector is used. Internal precision of multicollector 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb analyses is better than 0.01% (1σ), with 208Pb/206Pb and 207Pb/206Pb having precision better than 0.002% (1σ). Analyses are corrected for fractionation with respect to NBS-981. The fractionation factor averages 0.12 ± 0.03% per amu for analyses with 208Pb > 1´10‑11 amps and filament temperatures between 1250 – 1450°C. Total procedure blanks for common Pb analyses are typically below 10 pg. Analyses of U in whole rock or environmental samples can be done either as U oxide or U metal. For analyses in which the minor isotopes (234U and 236U) are important, we load the sample on zone-refined Re and analyze the metal ions using the Daly detector. When needed, a mixed 233U-235U spike is added to the samples. When analyses of minor isotopes are not important, samples are analyzed as oxides, either in static multicollector mode or with the Daly detector for small samples. Total procedure U blanks are typically below 2 pg.
Uranium
Analyses of U in whole rock or environmental samples can be done either as U oxide or U metal. For analyses in which the minor isotopes (234U and 236U) are important, we load the sample on zone-refined Re and analyze the metal ions using the Daly detector. When needed, a mixed 233U-235U spike is added to the samples. When analyses of minor isotopes are not important, samples are analyzed as oxide, either in static multicollector mode or with the Daly detector for small samples. Total procedure U blanks are typically below 2 pg.