New measurement of the 238U decay constant with inductively coupled plasma mass spectrometry
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The 238U decay constant (λU-238) is fundamental to radioisotope-based chronometry in the Earth and planetary sciences, yet only a single published λU-238 value (Jaffey et al. in Phys Rev C 4(5):1889–1906, 1971) is widely applied. We have determined λU-238 via the novel approach of measuring of 234Th ingrowth in high-purity 238U solutions, using isotope dilution mass spectrometry (ID-MS). The 234Th decay constant (λTh-234) was measured via decay counting with high-purity Ge (HPGe) γ detectors. Preliminary results for λU-238 agree with the value determined by α-counting  within the elevated uncertainty of 0.462% (k = 2). Ongoing efforts to reproduce λU-238 with reduced experimental uncertainties will inform future conclusions.
KeywordsUranium Thorium Half-life Decay constant Radiochronometry Inductively coupled plasma mass spectrometry
This document, LLNL-JRNL-752487, was prepared by LLNL under Contract DE-AC52-07NA27344. The authors thank Dave Ruddle of LLNL for engineering support, and T. Mark Harrison of the University of California, Los Angeles for his early support in advocating the needs of geochronology. This work was supported by LLNL’s laboratory directed research and development (LDRD) program (16-LW-053). TPD also gratefully acknowledges support from the US Department of Homeland Security National Technical Nuclear Forensics Center post-doctoral fellowship.
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