Radiocarbon Dating
Radiocarbon dating (¹⁴C dating) is used to determine the age of organic materials and carbonate-bearing samples. It is applied in a wide range of disciplines, including archaeology, Quaternary research, soil science, geology, palaeoclimate research, and environmental sciences. The method is suitable for samples up to approximately 50,000 years old.
At CologneAMS ↗, 14C samples are measured using accelerator mass spectrometry (AMS). Within available capacity, the research group Organic Geochemistry & Radiocarbon Dating ↗ also provides 14C measurements for external users. Processing times are currently approximately 3 to 5 months from sample arrival. Shorter turnaround times for small batches may be possible by prior arrangement.
Services | Sample Types | Preparation & Data Evaluation | External Users | The Radiocarbon Method | Literature
Services
Standard Services
- Sample preparation
- Measurement at CologneAMS
- Conversion and calibration of measurements
Optional Additional Services
- Photographic documentation of samples and/or sample preparation
- Detailed report
Sample Types
At CologneAMS, a wide range of materials is routinely processed for ¹⁴C analysis. These include:
| Charcoal | Minimum sample amount: 10–20 mg. |
|---|---|
| Wood/plant remains/seeds | Minimum sample amount: 20–100 mg. |
| Sediments/soils/peat | Required sample amount: 1 to 5 g maximum. |
| Bones | Required sample amount: 1–3 g. Long bones, such as tibia, or teeth with roots are preferred. Please do not label the bone directly. Instead label the packaging only. |
| Carbonates | Required sample amount: 30–100 mg. |
| CO₂ | Minimum sample amount: 50–70 µg.Ideal sample container: glass ampoule (5 cm × 0.5 cm Ø).Other sample containers: by prior arrangement. |
| Testing of bio-based materials | By prior arrangement. |
Please submit your samples in a condition suitable for analysis whenever possible. The material to be dated should be carefully selected in advance and cleaned of any components not intended for dating, as well as visible contaminants such as fibres or adhering particles. To prevent bacterial or algal growth, samples should then be dried at low temperature (approx. 50 °C).
Please prepare and package the samples in an environment with as little dust as possible, for example under a fume hood, and use clean, clearly labelled sample containers such as ziplock bags, glass vials, or plastic containers. Do not use aluminium foil or cardboard containers, as these may cause contamination. The labels on the sample containers must match the information provided in the submission form.
Additional selection or preparation steps may result in extra costs.
Sample Preparation and Data Evaluation
Before measurement, samples are prepared according to material type to remove contamination and isolate the carbon fraction suitable for radiocarbon dating.
Organic Material
Organic samples are first inspected under a microscope to remove visible contamination. Most materials, including marine and lacustrine sediments, charcoal, and plant remains, are then treated using a standard acid-alkali-acid extraction (AAA/ABA). This pretreatment aims to remove inorganic carbon as well as humic substances that may have been introduced from other depth intervals and could distort the results.
In the standard AAA pretreatment, carbonate components are removed by treating the sample with diluted hydrochloric acid (HCl). For carbonate-rich samples, this step may be repeated until the reaction has ceased. The residues are then thoroughly rinsed with Milli-Q water to remove residual acid.
In the next step, diluted sodium hydroxide (NaOH) is used to extract humic acids from the sample. If required, this fraction can be collected separately and the dissolved humic acids precipitated with concentrated HCl. For very small samples, the extraction time is reduced and the alkali step is omitted.
The acid- and alkali-insoluble residue is then treated with HCl once more to remove CO₂ that may have been absorbed from the atmosphere during the alkali extraction. Finally, the humin fraction is rinsed again with Milli-Q water and dried.
Bones
Bone samples are first cleaned mechanically and, in the case of organic contamination, additionally treated with organic solvents. We currently use a collagen extraction method without ultrafiltration, as removing the glycerol layer from the filters is difficult and could contaminate the sample material. The samples are then decalcified using diluted hydrochloric acid.
After decalcification, the material is converted to gelatine under slightly acidic conditions at approximately pH 3 and 60 °C. The hot collagen fraction is then filtered through glass fibre filters, freeze-dried, and used for radiocarbon dating.
Carbonates
Visible surface contamination is first removed mechanically from carbonate samples, followed by treatment with Milli-Q water in an ultrasonic bath. After etching with diluted hydrochloric acid, the outermost layer is removed by rinsing with Milli-Q water. After drying, the sample is crushed and transferred to a closed reaction vessel. Under argon, CO₂ is released using 85% phosphoric acid at 75 °C for 6 hours. The CO₂ is then carried with argon through the hydrolysis system to the graphitisation unit.
Conversion and Calibration of Results
Dating results are reported in tabular form as 14C concentrations and conventional radiocarbon ages in “years before present” (BP), each with a 1-sigma measurement uncertainty. For conventional radiocarbon ages, the year 1950 is used as the reference point. To improve comparability, 14C contents are also normalised to defined 13C values to correct for differences caused by isotopic fractionation.
However, a radiocarbon age does not directly correspond to a calendar age, as atmospheric 14C concentrations have varied over time. In addition, marine and lacustrine samples may be affected by reservoir effects, which result from the delayed carbon exchange between the atmosphere and the ocean or lake, as well as from circulation processes.
For this reason, radiocarbon ages are converted into calendar ages using calibration curves and are graphically presented as cal BP or cal BC/AD. In certain time intervals, during which atmospheric 14C production or concentration varied strongly, age determination may be limited or impossible.
For relatively young samples that are only a few thousand years old and contain approximately 1 mg of carbon after chemical preparation, the measurement uncertainty is generally around ± 30–40 years. Measurement uncertainty increases with increasing sample age and decreasing sample size.
External Users
The Organic Geochemistry & Radiocarbon Dating ↗ research group also processes samples from external users for 14C analysis at CologneAMS. For individual consultation and price information, please contact Barbara Bock (PhD). For further scientific or methodological questions, please contact Prof. Dr. Janet Rethemeyer.
Consultation and Sample Submission
Barbara Bock, PhD
+49 221 470 91044
bbock(at)uni-koeln.de
Head of the Organic Geochemistry & Radiocarbon Dating Research Group
Prof. Dr. Janet Rethemeyer
+49 221 470 7317
janet.rethemeyer(at)uni-koeln.de
Head of the 14C Laboratory
Dr. Jan Melchert
+49 221 470-89805
jan.melchert(at)uni-koeln.de
14C Sample Preparation
Svetlana John-Melchert (CTA)
+49 221 470-6617
lana.john(at)uni-koeln.de
Sample Submission
Before shipping your samples, please complete the following steps:
1. Fill in the submission form with all required sample information.
2. Ensure that each sample container is labelled clearly and securely to avoid delays or mix-ups.
3. Check that the labels on the sample containers match the information provided in the submission form.
4. Email the completed form to our office at bbock@uni-koeln.de and include a printed copy of the form with your samples.
5. Send your samples to:
Prof. Dr. J. Rethemeyer
Institut für Geologie und Mineralogie
Zülpicher Str. 49b
50674 Köln
The Radiocarbon Method
Carbon has three naturally occurring isotopes. The two most abundant are the stable isotopes 12C, with 98,89%, and 13C, with 1,11%, whereas the radioactive isotope 14C occurs only in very small amounts, at approximately 1,176 x 10-12 atoms per 12C atom.
14C is mainly produced in the stratosphere at an altitude of about 15–50 km through the interaction of cosmic-ray neutrons with nitrogen atoms (14N). In this reaction, a neutron is captured and a proton is released. The newly formed 14C is rapidly oxidised to 14CO2, which is taken up by plants during photosynthesis and subsequently enters the wider food chain through heterotrophic organisms.
Through exchange processes between the atmosphere, biosphere and hydrosphere, a dynamic equilibrium between 14C uptake and decay is established in living organisms. However, exchange rates between the individual carbon reservoirs vary strongly and depend on their respective turnover rates.
The death of an organism terminates this exchange with the environment. From this point onward, no new 14C is incorporated, and its concentration decreases continuously through radioactive decay. Based on the known half-life of 5,730 ± 40 years (Godwin, 1962), the remaining ¹⁴C-Konzentration concentration can be used to estimate the time elapsed since death.
After about 10 half-lives, or roughly 57,000 years, the 14C content in a sample has decreased to a level at which reliable dating is no longer possible. Very young samples, such as recent soils or active soil horizons, are difficult to date meaningfully because they still exchange carbon with the atmosphere and therefore show no clear decrease in 14C concentration.
Measurement results are initially reported as radiocarbon ages in “years before present” (BP), using 1950 as the reference year. Because atmospheric 14C concentrations have varied over time, radiocarbon ages are not identical to calendar ages and must be converted using appropriate calibration curves. For marine and lacustrine samples, reservoir effects may also need to be considered during interpretation.
Additional literature
Probenpräparation für 14C-Analysen
- Fülöp, R.-H., Heinze, S., John, S. & Rethemeyer, J. (2013). Ultrafiltration of bone samples is neither the problem nor the solution. Radiocarbon, 55, 491–500. DOI: 10.1017/S0033822200057623.
- Rethemeyer, J., Dewald, A., Fülöp, R., Hajdas, I., Höfle, S., Patt, U., Stapper, B. & Wacker, L. (2013). Status report on sample preparation facilities for ¹⁴C analysis at the new CologneAMS centre. Nuclear Instruments and Methods in Physics Research Section B, 294, 168–172. DOI: 10.1016/j.nimb.2012.02.012.
- Wacker, L., Fülöp, R., Hajdas, I., Molnár, M. & Rethemeyer, J. (2013). A novel approach to process carbonate samples for radiocarbon measurement. Nuclear Instruments and Methods in Physics Research Section B, 294, 214–217. DOI: 10.1016/j.nimb.2012.08.030.
Compound-Specific 14C Applications
- Kusch, S., Rethemeyer, J., Schefuß, E. & Mollenhauer, G. (2010). Controls on the age of vascular plant biomarkers in Black Sea sediments. Geochimica et Cosmochimica Acta, 74, 7031–7047. DOI: 10.1016/j.gca.2010.09.005.
- Mollenhauer, G. & Rethemeyer, J. (2009). Compound-specific radiocarbon analysis – analytical challenges and applications. Earth and Environmental Science, 5, 1–9. DOI: 10.1088/1755-1307/5/1/012006.
- Rethemeyer, J., Kramer, C., Gleixner, G., John, B., Yamashita, T., Flessa, H., Andersen, N., Nadeau, M.-J. & Grootes, P. M. (2005). Radiocarbon analysis of functional-defined and molecular organic matter fractions from agricultural soil profiles. Geoderma, 128, 94–105. DOI: 10.1016/j.geoderma.2004.12.017.
- Rethemeyer, J., Kramer, C., Gleixner, G., Wiesenberg, G. L. B., Schwark, L., Andersen, N., Nadeau, M.-J. & Grootes, P. M. (2004). Complexity of soil organic matter: AMS ¹⁴C analysis of soil lipid fractions and individual compounds. Radiocarbon, 46, 465–473. DOI: 10.1017/S0033822200039771.