New measurement of the 238U decay constant with inductively coupled plasma mass spectrometry

The U-238 decay constant (lambda(U-238)) is fundamental to radioisotope-based chronometry in the Earth and planetary sciences, yet only a single published lambda(U-238) value (Jaffey et al. in Phys Rev C 4(5):1889-1906, 1971) is widely applied. We have determined lambda(U-238) via the novel approach of measuring of Th-234 ingrowth in high-purity U-238 solutions, using isotope dilution mass spectrometry (ID-MS). The Th-234 decay constant (lambda(Th-234)) was measured via decay counting with high-purity Ge (HPGe) gamma detectors. Preliminary results for lambda(U-238) agree with the value determined by alpha-counting [1] within the elevated uncertainty of 0.462% (k = 2). Ongoing efforts to reproduce lambda(U-238) with reduced experimental uncertainties will inform future conclusions.