Accelerator mass spectrometry for the detection of ultra-low levels of plutonium in urine, including that excreted after the ingestion of irish sea sediments

Currently, most methods for the quantitative assessment of ²³⁹Pu have minimum detection levels (25 μBq for α-particle spectrometry) that are much higher than the levels of this isotope in many human bioassay and environmental samples. Accordingly, a priority has existed to develop methods that are more sensitive. Fission-track and ICP-MS methods have been used, but these can suffer either from an uncertain level of removal and/or recovery of uranium or from isobaric mass interferences. Accelerator mass spectrometry (AMS) has no such disadvantages, and its demonstrated detection limits for plutonium isotopes approach levels of attograms, equivalent to about 500 nBq for ²³⁹Pu. This paper describes the application of AMS to the measurement of ²³⁹Pu in urine produced by youths living in London (3.5 μBq day^-1) and by adults (~2-260 μBq day^-1), some of whom were exposed occupationally. In addition, an experiment was undertaken to measure the fasted absorbed fraction of ingested plutonium after the ingestion of 15 g of Irish Sea sediment by a volunteer. The measured absorbed fraction was 4.5 x 10^-5. It is concluded that accelerator mass spectrometry is a suitable method for the ultra-trace detection of plutonium.