U-Pb ID-TIMS geochronology using ATONA amplifiers

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We document the performance of new ATONA ('aA to nA') amplifiers installed on an Isotopx Phoenix thermal ionisation mass spectrometer (TIMS) at Princeton University and evaluate their suitability for high-precision analyses of Pb and U isotopes in pg- to ng-size samples characteristic for U-Pb geochronology. The new amplifiers are characterised by low and stable noise levels comparable to 1012 to 1013 ohm resistors, response time 10-14 A (1 mV relative to a 1011 ohm amplifier or ca. 60 kcps). As such currents are routinely achievable for major Pb peaks of interest (205-208Pb) in natural samples containing more than ca. 10 pg Pb∗ (radiogenic Pb), we expect ATONA-Faraday detection to find broad applications in U-Pb geochronology. Its practical use for low-blank, radiogenic samples continues to require ion counting for 204Pb, either with a fixed Faraday-ion counter gain or using a dynamic two-step (e.g. FaraDaly) method. Routine adoption of ATONA-Faraday collection in place of ion counting for most major Pb and U isotopes has the potential to increase sample throughput and precision, both improving the accessibility of isotope dilution (ID)-TIMS geochronology and pushing this technique towards better reproducibility. © 2020 The Royal Society of Chemistry.
Journal of Analytical Atomic Spectrometry
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