Katherine Freeman, distinguished professor of geosciences at Penn State, uses it to follow crude oil compounds released from the 2010 Deepwater Horizon oil spill that were taken up by microbes living in sediments of the Gulf of Mexico.
More traditional uses of carbon dating also benefit from an AMS, because it provides more precise measurements of carbon-14 than other methods, and it can do so with incredibly tiny samples -- as small as 1 milligram.
An accelerator then increases the kinetic energy of the carbon ions to 10-30 million electron volts and moves them through a tube where a powerful electromagnet makes them change direction. Because carbon-14 decays over time, the amount of it in a sample indicates the age of the sample.
How much their path bends depends on their mass: Lighter ions bend more. Penn State will soon be home to an accelerator mass spectrometer (AMS) that will allow researchers all over the country to do high-precision carbon dating to address questions about Earth's past and present.
Carbon-13, a stable, nonradioactive isotope with six protons and seven neutrons, makes up another one percent.