Impacts on precision of the half-lives of U234 and Th230 using the Neptune MC-ICPMS with high ohmic resistors

The half-lives of ²³⁴U and ²³⁰Th are fundamental constants for U-series disequilibrium dating, as are well-characterized reference materials such as Harwell Uraninite (HU1) and CRM112A. Approximately a decade ago, the half-life values most widely used in Th/U dating were refined using multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) (Cheng et al. 2013), achieving precision levels of ±260 years for ²³⁴U and ±110 years for ²³⁰Th. More recently, internal statistical uncertainties for the ²³⁴U half-life have been reported to approach ±25 years through the use of high-ohmic resistors, careful compensation for isotope abundance differences using reference materials, and rigorous evaluation of instrumental tailing (Hu et al. 2025).

Here, we present precision tests performed with an MC-ICPMS equipped with high-ohmic resistor combinations on secular-equilibrium speleothem samples from Wilder Mann Cave (>2 Ma). Data were processed following the baseline and treatment protocols of Kerber et al. (2025), including cubic Hermite polynomial fits to characterize peak tailing and identification and quantification of uranium scattering (“ghost”) signals. Using this implementation, which combines 10¹³ Ω Faraday detectors with long-term gain stability tests, we determined U-series isotope ratios for the Wilder Mann samples bracketed by HU1 and calibrated against CRM112A. The resulting half-lives of ²³⁴U and ²³⁰Th are 245,810 ± 265 years and 75,580 ± 145 years, respectively, in agreement with previously published values. Additional experiments assessed the internal precision of ²³⁴U and ²³⁰Th measurements using a 10¹³ Ω Faraday cup and enabled re-evaluation of the equilibrium state of the HU1 reference material. We confirm that the HU1 batch used in this study is offset from secular equilibrium by ~1.5‰, consistent with earlier inferences. Finally, we apply this analytical setup to ancient cold-water coral samples from IODP Site U1317, demonstrating near–secular equilibrium behavior for materials older than 500 ka, with downcore ages extending to ~3 Ma based on Sr-isotope stratigraphy (Raddatz et al. 2014).

H. Cheng et al., Improvements in 230Th dating, 230Th and 234U half-life values, and U–Th isotopic measurements by multi-collector inductively coupled plasma mass spectrometry, Earth and Planetary Science Letters 371–372, 82 (2013).

 

Hsung-Ming Hu et al.,Sub-epsilon natural ²³⁴U/²³⁸U measurements refine the ²³⁴U half-life and U-Th geochronology.Sci. Adv.11,eadu8117(2025).DOI:10.1126/sciadv.adu8117

 

Kerber, I. K., Kontor, F., Mielke, A., Warken, S., and Frank, N.: Technical note: “U–Th Analysis” – open-source software dedicated to MC-ICP-MS U-series data treatment and evaluation, Geochronology, 7, 1–13, https://doi.org/10.5194/gchron-7-1-2025, 2025.

 

J. Raddatz, A. Rüggeberg, V. Liebetrau, A. Foubert, E. C. Hathorne, J. Fietzke, A. Eisenhauer, and W.-C. Dullo, Environmental boundary conditions of cold-water coral mound growth over the last 3 million years in the Porcupine Seabight, Northeast Atlantic, Deep Sea Research Part II: Topical Studies in Oceanography 99, 227 (2014).