236U/238U and 240Pu/239Pu isotopic ratios in small (2 L) sea and river water samples

Accelerator Mass Spectrometry (AMS) and alpha spectrometry were used to determine uranium (236U, 238U, 234U) and plutonium isotopes (239Pu, 240Pu) in sea and river water samples. Plutonium was separated by Dowex® 1 × 8 resin and UTEVA® resin was used for uranium purification. The measured 236U/238U isotopic ratios for surface water from the Atlantic Ocean, the Pacific Ocean and the Black Sea were in the order of 10−9, while values for river water were in the order of 10−8. These contaminations may be attributed to global fallout. A sample of the reference material IAEA-443, collected from the Irish Sea, showed, in accordance to the reference value, a ratio that was 103 times higher due to effluents from the reprocessing plant at Sellafield. These results underline the good suitability of 236U/238U as a tracer for hydrology and oceanography, and show that relatively small water samples are sufficient for the determination of 236U by AMS, which is not the case for plutonium with present techniques. The plutonium concentrations in our water samples could only be measured with large uncertainties and were in the order of 10−3 mBq/L (with the exception of the Irish Sea sample).

► Successful determination of 236U in small (2 L) water samples.
► Contribution towards establishing 236U as an oceanic tracer.
► Detection of anthropogenic contamination with 236U.
► Measurement of 240Pu/239Pu isotopic ratios.