Comparison of using UO− and UF5− for 233,236U AMS measurement

AMS measurements of 236 U (and 233 U) are increasingly used in nuclear environmental monitoring and oceanographic tracing studies. The standard practice of 233,236 U-AMS is to produce UO − anions from Cs-sputter ion sources using (U)Fe 2 O 3 or (U)FeO x H y as sample material. In this case, the UO − beam is usually quite steady, but it takes several hours to exhaust a typical sputter target. This makes the measurement of a large batch of low-level environmental samples very time consuming. This paper reports that if the same sample material is mixed with PbF 2 to produce UF 5 − anions instead, the measurement of such a fluorinated target can be fully completed within one third the time, and with several times higher overall detection efficiency. With some assumptions, the full-target-usage ionization efficiencies of UO − and UF 5 − are estimated to be ∼2.1% and ∼6.8%, respectively. The pros and cons of the UO − and UF 5 − methods are compared systematically.