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

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