Radiocarbon Dating Laboratory

Radiocarbon dating is based on the continuous decay of the radioactive isotope of carbon, ¹⁴C. Radiocarbon is incorporated into all living organisms in proportion to its concentration in the environment. When an organism dies, carbon is no longer incorporated into its tissues, but the radiocarbon present continues to decay at a known rate.

Two radiocarbon dating methods are used at the CEN: the AMS method (Accelerator Mass Spectrometry) and the radiometric method.

AMS dating is possible on very small samples (a few milligrams). The CEN has the equipment and expertise to prepare samples for AMS dating, which includes 2 major steps:

• Sample preparation by fractionation of their carbon components followed by oxidation and reduction to graphite. The graphite produced is pressed into a target for AMS measurement.Chemical processes are involved in this step.
• The counting in a particle accelerator, which involves specialized nuclear physics.

After the samples are received and labelled, we proceed with their chemical pre-treatments.

The next step is combustion, which produces carbon dioxyde (CO₂).

The CO₂ is then purified into a vacuum system.

The resulting ultra-pure carbon dioxyde gas is sealed into a glass tube with a torch.

It is this CO₂ tube that will be shipped to an external laboratory that has an accelerator mass spectrometry facility. This laboratory will convert the CO₂ into graphite, and this graphite will be counted in the accelerator.

For a small additional cost, the IRMS (Isotope Ratio Mass Spectrometry) measurement of the delta ¹³C of your samples can also be done.

With every shipment of many unknown-age samples we must add samples coming from oxalic acid transformation (which is the international standard reference material for all radiocarbon laboratories), inert samples to determine the background value (blanks) as well as known-age samples (secondary standards), coming from multi-laboratory calibration. This procedure assures a never-ending following of the quality, accuracy and precision of the results given to customers.

The radiometric method is still used at the CEN to date the larger samples (a few grams). It consists in extracting the carbon contained in an organic sample (wood, peat, charcoal, shell, etc.) and producing benzene (C₆H₆), a liquid compound in which carbon is highly concentrated.

The vials containing the benzene are then placed in a liquid scintillation counter to measure C beta radioactivity, which is proportional to the age of the sample.

Dates produced at the CEN radiochronology laboratory have permitted the construction of dating chronologies on various research themes, such as tree line fluctuations, Holocene dynamics of peatlands, forest fires, post-glacial sea level variations, age of ice wedges in permafrost, slope movements and land slides, paleosoils in sand dune and archeological applications.

The operational philosophy of the laboratory includes a follow-up, after each weekly counting period, of the statistical stability of the standard made from international reference material (oxalic acid) and of the background values. Moreover, several wood dates have benefited from a comparison with dates obtained by dendrochronology, a method precise to the year. For example, two publications report the use of radiocarbon dates from the CEN laboratory to help join floating tree-ring series (Lavoie & Payette, 1997, The Holocene, 7: 129-137; Arseneault & Payette, 1997, Ecology, 78: 1873-1883). Once joined and dated precisely, radiocarbon dates from these series have shown a very low bias in comparison to true ages.

The CEN radiochronology laboratory now offers Pb-210 dating. It is possible to count the following radionuclides: Pb-210, Cs-137, Am-241, Cd-109, Co-57 as well as Ra-226 (which is the average of Pb-214 and Bi-214) in sediments using the HPGe method (High-Purity Germanium detector).

A bigger quantity is required for samples that are dirty, dusty, sandy or with a high fraction of sediments

P.S. In some cases, it is even possible to date smaller quantities. Feel free to contact us to discuss about your smaller samples.

Samples must be dried, clearly identified and packed in plastic (or glass vials), or enveloped in aluminium foil or plastic bags (Ziploc type). Avoid packaging the samples in paper or other organic material.

Pick up the right form (AMS or Radiometric) and fill one for each submitted sample. Join the form(s) with your package of samples.

Please contact us to get the plastic vials used in our counter (the transfer of the samples and capping into these vials can also be done by us at the lab). Compact the samples as much as you can in the vial and, if possible, try to get a similar height of sample for every vial.

Fill the Pb-210 dating form for each core submitted for analysis. Join it with your batch of samples from your core.

The samples must be mailed out to this address :

RADIOCHRONOLOGY LABORATORY
c/o Guillaume Labrecque
Université Laval
Abitibi-Price Building, room 0248
2405, Rue de la Terrasse
Québec, QC CANADA
G1V 0A6

You'll be contacted via e-mail when your samples reach us at the laboratory.

Submitters from outside Laval University will receive a bill to the address they provided on the dating form after they get their results.

Submitters from Laval University must fill the internal service form, then send it to the unit from where the bill be paid. Your department administration will then send the PO number to us at the laboratory before we can proceed with the analyses.