U-Pb ID-TIMS geochronology using ATONA amplifiers
Publication Year
2020
Type
Journal Article
Abstract
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.
Keywords
geochronology,
U-Pb geochronology,
Isotopes,
Binary alloys,
Mass spectrometers,
Thallium alloys,
Thallium metallography,
Uranium metallography,
Princeton University,
Lead metallography,
Ions,
Lead,
Radiation counters,
Thermal insulating materials,
Broad application,
Gain stability,
High-precision,
Isotope dilutions,
Reproducibilities,
Thermal ionisation
Journal
Journal of Analytical Atomic Spectrometry
Volume
35
Pages
1207-1216
Full text