Actinides AMS for nuclear safeguards and related applications

The nuclear safeguards system which is used to monitor compliance with the Nuclear Non-proliferation Treaty relies to a significant degree on the analysis of environmental samples. Undeclared nuclear activities can be detected through determination of the isotopic ratios of uranium and plutonium in such samples. It is necessary to be able to measure plutonium at the femtogram level in this application, and measure the full suite of uranium isotopes (233-238U) where the total uranium content may be at the nanogram level. In this paper we describe the development of our accelerator mass spectrometry system for such analyses, with particular reference to recent improvements in our methods. The commissioning of a fast isotope cycling system for actinides has led to improved precision, with reproducibility of 4% for actinide isotope ratios. The background level for the key rare isotope 236U is found to be 8.8 fg, for total uranium content in the nanogram range, and is limited by 236U contamination rather than ion mis-identification. For plutonium the background is at the low femtogram level.