State-of-the-art carbon-14 dating facility coming to Penn State

A'ndrea Elyse Messer
May 01, 2015

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 dating has been used since the 1940s to determine the ages of archaeological finds. Modern methods in mass spectrometry, far advanced since their development in the 1970s, now enable carbon dating to be applied to a wide range of new problems. 

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. For scientists whose test material is rare, valuable, or extremely hard to collect, that's important. Douglas Kennett, professor of anthropology at Penn State, recently confirmed a correlation between the Maya Long Count calendar and the European calendar by AMS dating small slivers of wood from a carved Maya lintel.

Freeman and Kennett are co-directors of the new AMS Carbon-14 Laboratory, which is expected to be fully operational in early 2016. Archaeologists, environmental scientists, and other researchers produce thousands of potential AMS carbon-14 samples each year, but only two other high-precision AMS facilities exist in the United States, and access to them is limited. It can take up to six months to have a sample tested. The new Penn State lab, featuring a powerful Pelletron® accelerator built by the Wisconsin-based National Electrostatics Corporation, should ease that crunch considerably.

"Even though there are carbon-14 facilities around the world, science is still under-served," says Freeman. "The new facility is an exciting addition both for Penn State and for the larger scientific community. It will enable precise dating of carbon-containing material with ages stretching back over the past 50,000 years."

"This new facility will improve our ability to study human-environmental interactions where chronology is key," adds Kennett. "It will be helpful in areas where we really need to know the order of events." For example, mammoths went extinct near the end of the last Ice Age, but whether the changing climate, disease, humans, or a comet impact did them in is a matter of debate that might be resolved with more precise dating techniques.

How it works

Carbon dating works because there are three naturally-occurring isotopes, or forms, of carbon, known as carbon-12, -13, and -14. Carbon-12, with six protons and six neutrons, makes up the vast majority of carbon on Earth, nearly 99 percent. Carbon-13, a stable, nonradioactive isotope with six protons and seven neutrons, makes up another one percent. The tiny amount left, only one carbon atom in a trillion, is carbon-14. This isotope has six protons and eight neutrons and, crucially, is radioactive; over time, it decays to nitrogen-14 (with seven protons and seven neutrons).

The half-life of carbon-14 is about 5,730 years, which means it takes that long for half the radioactive 14 C atoms in a substance to decay. By measuring the ratio of carbon-14 to the other isotopes of carbon in a sample, researchers can determine that sample's age. The precision of Penn State's new instrument is impressive; it will be able to determine the age of samples from the past 10,000 years within 15 to 20 years.

Preparation counts

To get an accurate date with AMS, the sample must be completely pure. Since carbon exists all around us, opportunities for contamination are legion, and samples go through extensive processing to ensure their purity. After thorough cleaning, a small amount of the material is vacuum-sealed in a quartz tube, which is then heated to a high temperature to convert the material to carbon dioxide, water, and nitrous oxides.

Kennett currently directs the Human Paleoecology and Isotope Geochemistry Laboratory in the Department of Anthropology, where materials are prepared for carbon-14 analysis. Anything that contains carbon can be AMS-dated, including charcoal, hair, skin, carbonates, seashells, bone, wood, and teeth.

Currently, samples prepared here are sent to a high-precision AMS laboratory at the University of California, Irvine, for further preparation and testing. Soon, Penn State will complete the preparation process by converting the carbon dioxide to graphite targets that will be analyzed by the new AMS.

By the time the Penn State AMS facility is running at full tilt, it will be able to process and analyze up to 10,000 samples a year, from forensic cases, archaeological digs, and studies involving soil, sediment, water, and air. Once the initial equipment is in place and operating properly, refinements and additions will be made to broaden its potential applications.

"Eventually, we'd like to be able to look at individual molecules," says Freeman. "That would allow us to track the sources and fates of carbon at the molecular scale."

 

Katherine Freeman is Distinguished Professor of Geosciences, khf4@psu.edu. Douglas Kennett is Professor of Anthropology, djk23@psu.edu. The Penn State Accelerator Mass Spectrometry Laboratory will be administered by Penn State's Institutes for Energy and the Environment. Penn State's Office of the Vice President for Research and the Provost's Office funded the AMS machine. The National Science Foundation is funding peripheral laboratories and equipment.

  • Katherine Freeman

    Katherine Freeman, distinguished professor of geosciences at Penn State

    IMAGE: Patrick Mansell
  • Doug Kennett

    Douglas Kennett, professor of anthropology at Penn State

    IMAGE: Patrick Mansell
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Last Updated July 28, 2017