Protactinium-231: A new radionuclide for AMS

For the first time, an AMS system was used to determine concentrations of the actinide Protactinium-231. 231Pa has widespread applications in the earth sciences. It can be used for U-series disequilibrium dating, and 231Pa is an important tracer in Paleoceanography. The Pa isotopes were measured with the compact ETH/PSI-AMS facility TANDY operating at about 300 kV. The linearity of the AMS is documented with two standard-dilution experiments and first measurements of natural samples from very different climate archives are presented. Our results show that it is possible to determine 231Pa amounts in the lower femtogram (1 fg = 10−15 g) range with the TANDY. In natural samples, 231Pa concentrations between 1 and 4 pg/g (1 pg = 10−12 g) were measured with an average total error of 3% (one sigma). The average over all reproducibility of these first measurements was better than 2% with clear potential for improvement.