RadioCarbon Dating and Other Technologies
Georgios S. Polymeris
RadioCarbon Dating and Other Technologies
Georgios S. Polymeris
TYPE OF SAMPLES THAT CAN BE DATED
Archaeological - Environmental
Charcoal, wood, twigs and seeds
Antler and horn
Textiles and fabrics
Marine, estuarine and riverine shell
Corals and foraminifera
Paper and parchment
Resins and glues
Also, the following provided they contain charcoal, or carbonised matter
Industrial and Commercial
Products containing natural organic raw materials can be authenticated and dated with the Radiocarbon Technique. The method is based on the determination of the carbon-14 (14C), concentration in the samples under investigation. The presence of carbon-14 presumes the existence of natural raw materials in a product due to the fact that the living plant and animal organisms absorb the carbon-14 atoms selectively during the carbon cycle in the atmosphere and biosphere. In addition, the quantitative analysis of carbon-14 allows the determination of the age of the raw materials and therefore the age of the product, using the radiocarbon dating technique. This is because the initial carbon-14 content in a living organism, which will be used afterwards as a raw material, is being gradually reduced after its death according to the half-life of carbon-14 (5730 years). In recent years this has important applications in the biofuels and other products containing a certain amount of biomass whose percentage needs to be determined for standardization and control reasons.
The Radiocarbon Laboratory is part of the Laboratory of Archaeometry established by law is the National Centre for Scientific Research Demokritos and hence its certificate is officially valid.
The age determination of a sample using the radiocarbon dating method requires a substantial cost and effort from the laboratory involved. For that reason, before sampling a deeper speculation should precede concerning the specific purpose of the research, as well as the best way to accomplish it using absolute dating.
The most important question, which should be asked each time a sample is collected for dating, is whether this particular sample is directly related with the historical event or occupation layer whose age is required. For example, the radiocarbon age of a wood sample from a post, no matter how precise the dating will be by the laboratory, will not be directly related to the specific layer if the post was re-used. Also, as a big tree may live for a long time (100-200 years), if one determines the age of a wooden or charcoal sample originating from the inner rings of such a tree, the calculated age may be 100-200 years older than the date the timber was cut even if it was used for the first time. The event dated by the laboratory is the date of creation and growth of the plant, tree or animal and not the date that it was used as an object.
The answer to these questions is not always obvious in an excavation. However, it is necessary to pay special attention to this subject and to check all the possible interpretations before one could select the proper sample. A typical procedure is to separate the short-lived from the long-lived plants (e.g. short-lived nutritional plants, branches from a hearth instead of relatively large trunks of long-lived trees). There are ways to approach the date of use of uncertain samples, like charred wooden posts of large trunks by careful selection of the external tree-rings or taking multiple sequenced samples for the wiggle matching technique. This should be done with consultation with the laboratory’s personnel.
A point that should be stressed here is that for the best performance of the research a close collaboration between the archaeologist and the scientific staff of the laboratory is needed.
The collection of the samples for radiocarbon dating should ideally be done together with the laboratory personnel for best results. If this is not feasible, the person who will perform the sampling should have in mind the following rules:
REQUIRED QUANTITY OF SAMPLE
Conventional dating - radiometric technique (GPC)
The optimum required quantity of sample for the determination of reliable dates with the highest possible accuracy varies between radiocarbon laboratories according to the technique used.
Table 1 shows the required quantities for a full-size sample in the laboratory of NCSR Demokritos for different types of samples. In practise though, it is possible to date one third (1/3) of the indicated amount in the table. However, this may result to an increased measurement time and hence delays, as well as to an increase in the age uncertainty. Depending on the amount of sample available and the expected age of the sample the lab personnel will advise customers of the estimated uncertainty.
Accelerator Mass Spectrometry (AMS) Dating
Minute samples of the order of milligrams are also accepted and are dated with the Accelerator Mass Spectrometry technique. The laboratory of NCSR Demokritos performs a microscopic examination and mechanical cleaning of small samples and applies any necessary chemical pretreatment. Collagen test is also performed for the bone samples. Following that and photographing and archiving, aliquots of samples, depending on the initial quantity, are eventually sent for measurement to a collaborating accelerator laboratory abroad. The results are evaluated and treated statistically and a report is sent to the submitter.
The amounts of sample required for AMS dating are listed in Table 2.
DOCUMENTATION – SUBMISSION FORM
Every sample submitted for dating should be fully documented with all related archaeological information, which is needed for the laboratory staff to draw the conclusions. For that reason, for every sample, which will be sent to the laboratory a Submission Form should be filled in and attached to it. Please ask for the submission form from the staff of our laboratory.
The archaeological age estimation is requested as it helps the laboratory staff to decide about the chemical pre-treatment procedures and to access the measurement time required. Also, it important for the estimation of the expected age error according to the available amount of sample and the discussion with the submitter whether this is useful for his/her application.
The calibration curve has been expanded in 2013 to cover the full application period of the radiocarbon dating, that is back to about 45,000 years, with a new statistical improvement been applied in 2020. Therefore, we can supply nowadays calibrated ages for all this period either in BC/AD or in calibrated years BP.
Table 1. Optimum amount of clean sample from different sample types for conventional dating at NCSR Demokritos.
|SAMPLE TYPE||SAMPLE WEIGHT (g)|
|Turf peat||62 – 109*|
|Sediment||150 – 4000*|
* It depends on the content of carbon in these samples
Table 2. Amounts of most common types of samples required for AMS dating
|Sample type*||Amount required|
|Charred material of any kind||10-20 mg|
|Bone, antler, horn||2 g|
|Sea shells||2 g|
* For other types of samples please consult us.