Measurement of ²³⁶U on the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA)

In this paper we present the first comprehensive analysis of the 1 MV AMS system at the Centro Nacional de Aceleradores (CNA, Seville, Spain) for ²³⁶U studies in environmental samples. In the last years, this radionuclide has become key in the AMS community, due to the very demanding ²³⁶U/²³⁸U abundance sensitivities required for general applications. As we demonstrate, the AMS system at the CNA is able to achieve sensitivity for the ²³⁶U/²³⁸U ratio of about 3 × 10^-11 despite its compact design. The use of "²³⁹Pu"/²³⁸U ratio as a proxy for "²³⁶U"/²³⁵U background correction is proposed and tested with natural samples that were also studied on the 600 kV Tandy AMS system at the ETH Zürich. This correction is significant in the CNA case, due to the low mass resolving power of the low-energy spectrometer and to the lack of a third filter on the high-energy side. With the measurement of reference solutions supplied by the Institute for Reference Materials and Methods (IRMM-075), and reference natural matrixes provided by the International Atomic Energy Agency (IAEA-Soil-6, IAEA-375; 384; 386 and IAEA-RGU), we show that the 1 MV AMS system at the CNA can be routinely used for determinations of anthropogenic ²³⁶U at environmental levels.