The CAIS radiocarbon AMS facility houses two AMS units. The 500 kV NEC 1.5SDH-1 pelletron (CAMS) is a tandem accelerator equipped with a 134-cathode MC-SNICS negative ion source. During the AMS measurement, negative ions of carbon isotopes 12C, 13C and 14C are sequentially injected and accelerated towards the positive high voltage terminal. At the terminal, the negative ions undergo charge exchange collisions with argon gas atoms and become positive ions. The repulsion between the positive ions and the terminal causes further acceleration of the ions to a total energy of 1 MeV. After acceleration, each isotope is mass separated by magnetic field. 12C and 13C beams are measured in Faraday cups whereas the rare isotope 14C is measured using a particle detector.

         

The 250 kV NEC Single Stage AMS (SSAMS) is also equipped with the 134-cathode MC-SNICS ion source. SSAMS unit does not have a second stage acceleration, and the total beam energy is about 300 keV. This unit has a lower beam transmission compared to the CAMS unit, so it takes longer measurement time to achieve the same precision as that of CAMS. However, SSAMS unit requires much less maintenance than CAMS.

          

 

SUBMIT AMS SAMPLES

 

Background and History of Radiocarbon Dating

In 1946 American chemist Willard Libby predicted that there should be a significant difference in 14C activity between living organisms and fossil carbons due to the long half-life of 14C. In the following years, Libby and his team of researchers at the University of Chicago conducted a series of experiments testing this prediction and its implications. This research ultimately led to the publication of the first set of radiocarbon dates in 1949.

One of the greatest achievements of Libby and his team was that they devised a means of measuring the extremely low concentrations of 14C that are found in nature. Instead of counting 14C atoms directly, they used a Geiger-Müller counter to measure the radioactivity of solid carbon samples, inferring the concentration of 14C from the number of decay events over time, in counts per minute (cpm). Libby and his team measured the 14C activity of modern terrestrial organisms, and concluded that the concentration of 14C in living things was constant across time and space. Thus, it would be possible to calculate the 14C activity expected at a given time after the organic material was removed from the life cycle.

Libby and colleagues tested their method on known-age geological and archaeological materials. The first reported radiocarbon age was for a piece of wood taken from the tomb of Zoser, an Egyptian king who reigned from 2665 to 2650 BC. Radiocarbon age determinations from this and other historically dated Egyptian artifacts, as well as tree-ring dated wood samples––widely known as the “Curve of Knowns”––demonstrated “satisfactory” agreement between the expected and measured ages. Libby was awarded the Nobel Prize in Chemistry for his research on 14C dating in 1960.

Data Reporting

Standard turnaround time is 3 weeks. Turnaround time for rush samples is 7 business days. Please call ahead for turnaround times for sample quantities exceeding 30, or for rush samples requiring a turnaround time shorter than 7 business days.

The reported 14C age is corrected for isotope fractionation based on δ13C measured by IRMS. The error is quoted as one standard deviation and reflects both statistical and experimental errors. Standard deviations for full-size samples are typically ± 20–25 14C yr (0.1–0.25 pMC) for samples younger than 5,000 14C yr.

To achieve greater precision, multiple measurements can be made on the same sample to calculate a weighted average and error. Additional fees are charged for this service, as it requires different portions of the same sample to be pretreated, graphitized, and measured independently.

We are happy to include calibrated calendar ages in your report. There is no charge for this service.

Sample Pretreatment for AMS

Sample Pretreatment for AMS

In general, it should be assumed that all samples are affected by some form of alteration or contamination. Contaminants are carbon-containing materials that are not indigenous to the original organic material being dated. The goal of sample pretreatment is to isolate the carbon fraction required for radiocarbon dating and to remove carbon fractions that are altered or contaminated.

Selecting the appropriate pretreatment plan depends on the unique attributes of the sample itself, such as the sample type, potential contaminants, the burial context, and the size and preservation of the sample. Communication between the radiocarbon researcher and the sample collector is integral to this process.

Methods Used:

Physical pretreatment

All samples are physically examined to evaluate the composition and preservation of the sample, and to determine the appropriate pretreatment plan. In many cases further physical pretreatment is required. This may involve cleaning to remove obvious contaminants and/or reduction of particle size of the sample.

Cleaning involves the physical, rather than chemical, removal of obviously intrusive materials. Some common contaminants include intrusive rootlets, which are manually separated from the sample using forceps, and surface dirt. Depending on the sample type, surface dirt may be removed by washing in an ultrasonic bath or by physically removing the outermost layer of the sample using a rotary tool or scalpel.

In some cases, samples are sieved to select an appropriate size fraction, or gently crushed to reduce the size of the particles.

Chemical pretreatment

The goal of chemical pretreatment is to remove contaminants that are chemically soluble. Certain chemical pretreatment techniques are considered routine for specific sample types or contaminants, and are described below. However, the implementation of these techniques may vary depending on the size and condition of the sample.

Acid/Alkali/Acid (AAA)

The AAA method is used to pretreat a wide variety of sample types including plant material, charcoal, wood, soils, sediment, peat, and plant-based textiles. This involves three steps: (1) an acid treatment to remove secondary carbonates and acid-soluble compounds; (2) an alkali treatment to separate out humic acids; and (3) a second acid treatment to remove atmospheric CO2. For small or poorly preserved samples, the alkali treatment may be shortened or omitted completely, or humic acids may precipitated out of alkali solution for radiocarbon dating.

The sample is placed 1N HCl and heated to 80ºC for 1 hour, centrifuged and decanted. The sample is then washed with 0.1 M NaOH to remove possible contamination by humic acids. The sample is then treated with dilute HCl, washed with deionized water and dried at 105ºC.

Hot HCl

Soils and sediments are treated with hot acid to remove carbonates and acid-soluble compounds. The sample is placed in 1N HCl and heated to 80ºC for 1 hour, centrifuged, and decanted. The sample is rinsed in deionized water and dried at 105ºC.

Collagen extraction

Collagen is a fibrous structural protein in the extracellular space in bone and tissues. The collagen fraction, with the mineral portion (bioapatite) removed, is the preferred material for radiocarbon dating bone samples when preservation permits.

The physically pretreated bone sample is broken into smaller particles, but not pulverized, to increase the surface area. The sample is treated with cold (4ºC) 1 N HCl for 24 hours to demineralize the bone. The residues are filtered, rinsed with 0.1N NaOH to remove humic acids, then rinsed with HCl to remove CO2 absorbed from the atmosphere. The sample is rinsed in deionized water to pH 4 (slightly acidic) and heated at 80ºC for 8-12 hours. The solution is then filtered through a fiberglass filter, and dried to isolate the total acid insoluble fraction (“collagen”).

Acetic acid hydrolysis (bioapatite protocol)

In cases where bone samples contain little or no collagen due to poor preservation or calcination, properly pretreated bone bioapatite can provide reliable dates if the secondary or diagenetic carbonates can be removed. An acetic acid pretreatment is used to isolate the bioapatite from tooth enamel, fully cremated bone, and poorly preserved bone samples. Bioapatite forms a relatively stable crystalline lattice, and is not soluble in weak acids. Secondary carbonates can be removed using 1N acetic acid.

An aliquot of the sample is gently crushed into ~1 mm fragments and reacted with 1N acetic acid in a flask, which is evacuated and re-pressurized periodically. The sample is allowed to react overnight. When the reaction ceases, the cleaned sample is rinsed repeatedly in deionized water and dried at 60ºC.

HCl surface leaching

This pretreatment is used to remove the exterior surface of carbonate samples that are suspected of recrystallization, exchange, or substitution. The sample is placed in a volume of 1N HCl necessary to reduce the sample weight by at least 10% in a warm ultrasonic bath until CO2 evolution ceases. The sample is rinsed repeatedly in deionized water and dried.

Organic solvent extraction

Museum preservation treatments may employ waxes, resins, oils, or glues that contaminate the organic fractions of bones or wooden objects. These materials can be removed using organic solvents such as acetone.

 

Isolating Carbon for AMS

After the appropriate pretreatment procedures, the carbon in the sample must isolated in the form of graphite for analysis via AMS. The carbon is first converted to a gas in the form of CO2 through acid hydrolysis for inorganic carbonates such as shell and bioapatite, and combustion for noncarbonates such as collagen and charcoal. The purified CO2 gas derived from the sample is converted to a solid, graphitic carbon for analysis.

 

Methods Used:

Acid hydrolysis

Pretreated carbonate samples such as shells, foraminifera, and bioapatite are reacted with 100% phosphoric acid (H3PO4) in a closed, evacuated glass vessel to produce CO2. Dissolved inorganic carbon (DIC) is produced from water samples using 85% phosphoric acid in a closed, evacuated glass vessel.

Combustion

Pretreated soils, sediments, and other organic-content materials are sealed in evacuated quartz ampoules containing CuO and combusted at 900ºC to produce CO2. Collagen samples are combusted at a lower temperature, 575ºC, in Pyrex ampoules.

Purification of CO2

The CO2 produced from acid hydrolysis or combustion is cryogenically purified from other reaction products, such as water vapor and nitrogen gas, and condensed in traps on a vacuum line using liquid nitrogen. In some cases, additional steps are required to remove other impurities, such as sulfur.

Graphitization

The purified CO2 gas derived from the sample is converted to a solid, graphitic carbon. This is achieved by reducing the CO2 in the presence of hydrogen (H2) at 580ºC in an evacuated, closed system in the presence of iron. The iron ­functions as a catalyst, thermal conductor, and binder which facilitates handling of the graphitized carbon. Water, which is formed as the reaction proceeds, is absorbed by magnesium perchlorate.

 

Amount of Sample Required for Analysis:

A minimum of 100 μg of graphitic carbon is required for analysis. The amount of untreated sample required to obtain this minimum size depends on the type of material being studied and the condition/preservation of the sample. Whenever possible the optimum, rather than minimum, sample size should be submitted. If you have any questions, you are welcome to contact our scientific staff concerning your samples.

 

Sample Submission Guidelines

Sample submission guidelines:

If you are a first-time client, please contact us before sending your samples. We do not provide services for private individuals, only businesses, nonprofit organizations, governments, and academic institutions. 

  1. Package samples in clean, well-labeled, tightly sealed, crush-proof containers. Use the sample size table to determine the optimum sample size based on the material type.
  2. Complete the radiocarbon dating sample submission form. If you are sending more than one sample, you can put them all on the same form. Make sure you assign each sample a unique identifier. Include a printed copy of the form in the package.
  3. Note: If you are sending 10 or more samples, please also send us an electronic sample inventory (excel file)—you also qualify for a 10% volume discount.
  4. Address the package to:

Radiocarbon Dating Lab
Center for Applied Isotope Studies
120 Riverbend Road
Athens, GA 30602 USA

 

FAQ

Will I get the rest of my samples back?

Our policy is to archive excess sample materials. If you would like us to return the unused portion of your samples, please let us know and we will prepare the materials for shipping at your expense.

 

Do you provide services for private individuals?

No, we only provide consulting services for academic institutions, governments, nonprofit organizations, and commercial operations.

 

How much sample should I send? What is the smallest sample you can measure?

It depends on the type of material you are working with. “Minimum” and “optimum” sample sizes are included in the fees chart. If your sample is smaller than the minimum, or is a material not listed, please contact us.

 

How much does radiocarbon dating cost? What is included in this fee?

Most samples are $450; bones are $500. We report conventional radiocarbon age (14C yr BP), percent Modern Carbon (pMC), δ13C, as well as calibrated calendar dates (by request). For certain material types, we also report δ15N or δ18O. See fees chart for details.

 

Can I get a discount?

We offer 10% volume discount for batches of 10 or more samples. We also offer discounts for researchers affiliated with the University System of Georgia and Emory University. Contact us for details.

 

When will I get results?

The turnaround time for most standard analyses is 2–3 weeks. Large batches or samples requiring additional analysis may take longer. Please contact us for details.

 

How should I package my samples?

There are many acceptable methods, but the most important things to consider are that they are clearly labeled and easy to open and close. We prefer tightly-sealed glass or plastic vials for small or delicate samples. Plastic bags and aluminum foil are usually fine for larger samples. We prefer see-through containers when possible.

 

Meet the AMS Team
Alex Cherkinsky

Alex Cherkinsky

Senior Research Scientist


Carla S. Hadden

Research Scientist


Hong Sheng

Research Technician III


Jana Maure Carpenter

Lab/Research Technician I


Matthew H. Colvin

Graduate Research Assistant


Jordan T. Chapman

Graduate Research Assistant