First Protactinium-231 measurements using the MILEA AMS system

We present an AMS-based method for measuring 231 Pa at natural levels in environmental samples. A chemical procedure extracts 231 Pa from sea sediments using 233 Pa as a reference isotope. 233 Pa was separated from its mother-nuclide 237 Np via single-step extraction chromatography. AMS measurements at the Multi-Isotope-Low-Energy AMS System (MILEA) at ETH Zürich showed no interference from 232 Th . We determined a 231 Pa concentration of (3.6 ± 0.6) × 10 9 atoms/g in the IAEA-385 reference material (Irish Sea sediment). We report on the development and implementation of a measurement procedure for 231 Pa AMS, demonstrating its potential for ultra-trace environmental studies. • Development of a measurement procedure for 231 Pa in environmental samples using AMS. • Separation of 233 Pa from a 237 Np solution using the TK400 resin. • No interference from the much more abundant 232 Th during AMS measurements. • First determination of 231 Pa concentration for the IAEA-385 reference material (Irish Sea sediment).