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The age of plutonium is defined as the time since the last separation of the plutonium isotopes from their daughter nuclides. In this paper, a method for age determination based on analysis of 241 Pu/ 241 Am and 240 Pu/ 236 Pu using ICP-SFMS is described. Separation of Pu and Am was performed using a solid phase extraction procedure including UTEVA, TEVA, TRU and Ln-resins. The procedure provided separation factors adequate for this purpose. Age determinations were performed on two plutonium reference solutions from the Institute for Reference Materials and Measurements, IRMM081 ( 239 Pu) and IRMM083 ( 240 Pu), on sediment from the Marshall Islands (reference material IAEA367) and on soil from the Trinity test site (Trinitite). The measured ages based on the 241 Am/ 241 Pu ratio corresponded well with the time since the last parent-daughter separations of all the materials. The ages derived from the 236 U/ 240 Pu ratio were in agreement for the IRMM materials, but for IAEA367 the determination of 236 U was interfered by tailing from 238 U, and for Trinitite the determined age was biased due to formation of 236 U in the detonation of the "Gadget".

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Cryoturbation in high-latitude soils is crucial for the long-term cycling of elements, but the rates of soil motion are poorly constrained. Here, we test whether the rate of frost creep, soil erosion and vertical soil mixing in frost boils can be estimated using short-lived radionuclides ( 137 Cs and 210 Pb). We find a small-scale variation in 137 Cs and 210 Pb inventories in the lower levels of the eroding regions of frost boils in comparison to the expected depositional sites; hence, the distribution of the radionuclides appears to reflect a lateral transport of atmospheric fallout from the centre of the boil (inner domain) towards the surrounding soil (outer domain). 14 C dating of the soil indicates that fallout of 137 Cs was mobile in the soil and that 210 Pb moved with the soil matrix. A soil creep model and a surface soil erosion model are derived and applied to the lateral and vertical distributions of 210 Pb in the frost boil. Both models predict the expected trajectories of soil motion and provide rates of creep, erosion and mixing at a mm yr À1 to cm yr À1 scale. The distribution of 210 Pb provides new insights about the processes and rates of soil mass movement in frost boils, if sound mass-balance models are applied.

The mobility of uranium, neptunium, plutonium, americium and curium from spent nuclear fuel (U0 2 ) into compacted bentonite was studied. Pieces of spent BWR U0 2 fuel was embedded in a compacted bentonite clay/low saline synthetic groundwater system. After a contact time of six years the bentonite was sliced into 0.1 mm thick slices and analysed for its content of actinides. Radiometric as well as inductively coupled plasma mass spectrometry (ICP-MS) were used for the analysis. The influence on the mobility by the addition of metallic iron, metallic copper and vivianite (Fe(II)-mineral) to the bentonite clay was investigated. The results show a low mobility of actinides in bentonite clay. Except for uranium the mobility of the other actinides could, after six years of diffusion time, only be detected less than 1 mm from the spent fuel.