Wet chemistry for AMS & isotope research

A laboratory at the heart of our isotope research

Before a single atom can be counted on an accelerator, the real work happens at the bench. The DFNA Chemistry Laboratory is where rocks, sediments, water, bone and ancient artefacts are turned — gram by careful gram — into samples clean enough to measure. It is the wet-chemistry backbone of our isotope work: its main job is preparing targets for the RoAMS 1 MV Tandetron AMS, though it runs analytical chemistry of its own as well.

Because AMS detects individual atoms at ratios as low as 1 in 10¹⁵, the chemistry has to be exquisite: low blanks, contamination control, well-characterised yields, and a deep understanding of the matrix being processed. This is where physicists, chemists, geologists, geographers, archaeologists and environmental scientists meet—around the bench.

Physics Chemistry Geology Geography Archaeology Environmental science Biology

Radiocarbon (¹⁴C) is a naturally occurring radioactive isotope of carbon. While an organism is alive, it exchanges carbon with the atmosphere; once it dies, its ¹⁴C decays at a known rate. Measuring how much remains tells us when that exchange stopped—the basis of radiocarbon dating.

First proposed by Willard F. Libby in 1946 and recognised with the Nobel Prize in Chemistry in 1960, radiocarbon dating has fundamentally reshaped archaeology, palaeoclimate science and environmental research. Since 1977, the use of AMS has revolutionised the field: instead of waiting for atoms to decay, AMS counts the ¹⁴C atoms directly, cutting sample sizes from grams to milligrams, shortening analysis times, and improving accuracy.

In our lab, every ¹⁴C measurement begins on the bench. Organic samples—wood, charcoal, peat, bone, textiles, shells, sediments—first go through an acid–base–acid (ABA) pretreatment: a hot acid wash dissolves carbonates, an alkaline step removes mobile humic acids, and a final acid rinse strips any reabsorbed atmospheric CO₂. Bone is treated more gently to isolate its collagen.

The cleaned material is then combusted in an elemental analyser to release pure CO₂ (carbonates are instead digested in acid in the carbonate-handling system). That CO₂ is catalytically reduced over an iron powder catalyst under hydrogen at ~580 °C in our automated graphitisation (AGE3) reactors, condensing the carbon into solid graphite. The graphite is pressed into aluminium cathodes—the targets RoAMS actually measures.

The accuracy of a ¹⁴C date depends as much on the quality of this chemistry as on the spectrometer itself. Tight blank control, careful matrix-specific procedures and well-characterised reference materials are what make our chronologies reliable—from a few centuries back to roughly 50,000 years before present.