Determination of U-236 in sediment samples by accelerator mass spectrometry

²³⁶U is produced only by neutron irradiation of uranium and therefore is potentially useful as a marker for anthropogenic uranium in the environment. Accelerator mass spectrometry (AMS) provides a technique for the determination of very low concentrations of actinide nuclides, and has now been applied to the determination of ²³⁶U : ²³⁵U ratios in an intertidal sediment core collected from the North Irish Sea. Combining measurements of the ²³⁸U mass concentrations calculated from alpha spectrometry with ²³⁸U : ²³⁵U ratios from ICP-MS and ²³⁶U : ²³⁵U ratios from AMS has allowed the estimation of the mass concentrations of ²³⁶U in the sediments. ²³⁶U mass concentrations are in the range 10^-8 to 10^-9 g kg^-1, and ²³⁶U : ²³⁸U atom ratios in the range from 100^-5 to 1^-6, well above natural baseline levels. Uncertainties based on propagation of measurement errors were less than ±10% although ±15% is perhaps a more realistic estimate of overall uncertainty.