Quantification of plutonium in environmental samples at the University of Cologne, Germany: progress update

The measurement of ^239,240Pu in environmental samples can play a key role in investigating Anthropocene Earth (sub-)surface processes. As a consequence of atmospheric nuclear weapon tests conducted in the 1950s and 1960s, Earth’s outermost skin was supplied with fallout radionuclides (FRNs), providing distinct geochronological markers. The application of FRNs is well established, with ¹³⁷Cs being most commonly measured. However, ^239+240Pu activities are more decay-insensitive (t_1/2 ²³⁹Pu: ~24.1 ka; ²⁴⁰Pu: ~6.6 ka), there is less soil inventory contamination arising from nuclear power plant accidents than reported for ¹³⁷Cs, and only a few grams of sample material can be sufficient for a measurement. Ultimately, the (separate) quantification of ^239,240Pu inventories measured by Accelerator Mass Spectrometry (AMS) represents a further evolution step towards more precise measurements than achieved by other mass spectrometry or decay counting techniques.

The development of ^239,240Pu measurement capabilities at the Centre for Accelerator Mass Spectrometry (CologneAMS), University of Cologne (UoC), has given the go-ahead to exploit the wealth of possible ^239+240Pu applications to decipher modern Earth (sub-)surface processes in different settings. Based on tailored sample processing protocols applied at the Institute of Geology and Mineralogy and the Division of Nuclear Chemistry (both UoC), we present first results from a selection of ongoing projects. The sample processing workflow applied together with the AMS measurement precision achieved allows for resolving specific activities below ~5 mBq kg^-1. Accordingly, a spatial focus is laid on study sites where ultra-high precision of measurements is required (e.g., the Atacama Desert in northern Chile).

.