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Major, minor and trace uranium isotopes were measured at Lawrence Livermore National Laboratory in environmentally acquired samples using different instruments to span large variations in concentrations. Multi-collector inductively-coupled plasma mass spectrometry (MC-ICPMS) can be used to measure major and minor isotopes: 238 U, 235 U, 234 U and 236 U. Accelerator mass spectrometry (AMS) can be used to measure minor and trace isotopes: 234 U, 236 U and 233 U. The main limit of quantification for minor or trace uranium isotopes is the abundance sensitivity of the measurement technique; i.e. the ability to measure a minor or trace isotope of mass M in the presence of a major isotope at M ± 1 mass units. The abundance sensitivity for 236 U/ 235 U isotope ratio measurements using MC-ICPMS is around ∼2 × 10 −6 . This compares with a 236 U/ 235 U abundance sensitivity of ∼1 × 10 −7 for the current AMS system, with the expectation of 2–3 orders of magnitude improvement in sensitivity with the addition of another high energy filter. Comparing 236 U/ 234 U from MC-ICPMS and AMS produced agreement within ∼10% for samples at 236 U levels high enough to be measurable by both techniques.

Mass spectrometric methods provide sensitive, routine, and cost-effective analyses of long-lived radionuclides. Here we report on the status of work at Lawrence Livermore National Laboratory (LLNL) to develop a capability for actinide measurements by accelerator mass spectrometry (AMS) to take advantage of the high potential of AMS for rejection of interferences. This work demonstrates that the LLNL AMS spectrometer is well-suited for providing high sensitivity, robust, high throughput measurements of plutonium concentrations and isotope ratios. Present backgrounds are ∼2 × 10 7 atoms per sample for environmental samples prepared using standard alpha spectrometry protocols. Recent measurements of 239 + 240 Pu and 241 Pu activities and 240 Pu/ 239 Pu isotope ratios in IAEA reference materials agree well with IAEA reference values and with alpha spectrometry and recently published inductively coupled plasma–mass spectrometry (ICP–MS) results. Ongoing upgrades of the AMS spectrometer are expected to reduce backgrounds below 1×10 6 atoms per sample while allowing simplifications of the sample preparation chemistry. These simplifications will lead to lower per-sample costs, higher throughput, faster turn around and, ultimately, to larger and more robust data sets.