After pre-treating the samples so that we can be absolutely sure that what we are dating is what we are interested in, the next step is to get the samples into a form which can be measured by accelerator mass spectrometry (AMS). To do this, our samples are first homogenised in a sonic bath. This ensures that we are getting an average measurement from the sample rather than any part of the sample being over-represented in the final measurement. Following homogenisation, the samples are then dried in a freeze-drier and weighed. At this stage the samples undergo a pretty radical transformation.
Up until this point, the material we’ve been working with is still, strictly speaking, wood. But the next step is to completely combust the sample. During combustion, the carbon dioxide produced is captured. This CO2 is then graphetised using a zinc and iron reduction method. The amount of graphite produced from this method is small, but importantly is greater than 95% pure carbon (ie. graphite). The resulting graphite is then pressed into an aluminium cathode, and it is this small cathode which is loaded into a wheel with dozens of other samples. The wheel is then taken off to be measured – that process will be covered in the next post!