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Optimization of 186 Os/ 188 Os analyses by N-TIMS using amplifiers equipped with 10 13 Ohm resistors

Abstract : Analysis of 186 Os/ 188 Os variations in most natural samples is hampered by their low Os concentrations (usually <100 pg/g), requiring Os separation from up to a kilogram of powder to obtain high precision results. Recently developed amplifiers equipped with 10 13 Ohm feedback resistors improve the signal to noise ratio by an order of magnitude, allowing acquisition of high precision data (2SE <50 ppm) from 186 OsO 3 ion beams of ~40 fA, and thus analysis of less material (~10 to 500g). Factors controling the accuracy and precision of 186 Os/ 188 Os NTIMS analyses, using a mixed array of 10 13 and 10 11 Ohm amplifiers, include isobaric interferences, baseline variability, gain calibration, decay time corrections and oxygen isotope composition variations. Isobaric interferences present the greatest challenges, but these can be largely overcome by using double Pt filaments and periodically monitoring interferences during each analysis. The optimized procedures produce 186 Os/ 188 Os ratios with precisions close to the theoretical limits imposed by counting statistics and Johnson-Nyquist electronic noise for ion beams of 10 to 70 fA. The long term reproducibility (85 ppm; 2σ) approaches theoretically expected values (~50 to 80 ppm). This reproducibility is sufficient to allow 186 Os/ 188 Os analyses of crustal rocks, for which relatively large variations are expected.
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https://hal.univ-lorraine.fr/hal-03325882
Contributor : Laurie Reisberg <>
Submitted on : Wednesday, August 25, 2021 - 1:13:37 PM
Last modification on : Thursday, August 26, 2021 - 3:21:06 AM

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Laurie Reisberg, Catherine Zimmermann. Optimization of 186 Os/ 188 Os analyses by N-TIMS using amplifiers equipped with 10 13 Ohm resistors. Geostandards and Geoanalytical Research, Wiley, 2021, 45 (2), pp.287-311. ⟨10.1111/ggr.12371⟩. ⟨hal-03325882⟩

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