AMS detection of actinides at high mass separation

AMS is the mass spectrometric method with the highest abundance sensitivity, which is a prerequisite for measurement of the long-lived radioisotope ²³⁶U (t_1/2=23.4 million years). The most successful application so far is oceanography, since anthropogenic ²³⁶U is present in the world oceans at ²³⁶U:²³⁸U from 10^-11 to 10^-8. We have explored methods to increase the sensitivity and thus to reduce the water volume required to 1 L or less, which significantly reduces the sampling effort. High sensitivity is also necessary to address the expected typical natural isotopic ratios on the order ²³⁶U:²³⁸U = 10^-13, with potential applications in geology. With a second 90 analyzer magnet and a new Time-of-Flight beam line, VERA is robust against chemical impurities in the background, which e.g. allows measuring Pu isotopes directly in a uranium matrix. This simplifies chemical sample preparation for actinide detection, and may illustrate why AMS reaches lower detection limits than other mass spectrometric methods with nominally higher detection efficiency.