We operate an accelerator mass spectrometry (AMS)  service in the Centre for Accelerator Science (CAS) at ANSTO, the Australian Nuclear Science and Technology Organisation. Amongst the radioisotopes we measure is 14C or ‘radiocarbon’. AMS is a very sensitive analytical technique which is based on identifying and counting individual atoms, in this case of radiocarbon. Some of our clients/collaborators wish to distinguish between biogenic and fossil sources of carbon dioxide (CO2) and methane (CH4) and radiocarbon is an excellent way of doing this: the former have an essentially ‘modern’ ration of 14C/12C whereas the latter are depleted in 14C.  The samples are generally derived from waste water treatment plants, from soil gases, from boreholes around landfills or coal mines or from gas seeps in rivers. The concentration of CO2 and CH4 in these samples is generally high (several to tens of percent), much greater than typical atmospheric concentrations. This is why I can use relatively small volumes of ~ 0.5L. The sample processing involves removing water vapour, then separating the CO2 and finally separating the CH4 and converting it to CO2. The CO2 fractions are then converted into graphite, the solid form of carbon we need as a target in the accelerators. We have found Cali-5-Bond bags store the samples reliably for months unlike some other sampling bags that are on the market.

Dr. Andrew Smith

Sen. Prin. Research Scientist
NSTLI Centre Accelerator Science
www.ansto.gov.au