CNA

Centro Nacional de Aceleradores

C-14 laboratory

Samples (archaeological, artistic, historical, etc.) can be dated by measuring their 14C content. This radioisotope is produced naturally and has the same chemical behavior as other carbon isotopes.
 
At CNA, there is a Radiocarbon Dating Service (14C) associated to MiCaDaS Accelerator. This service includes a fully-equipped laboratory for sample preparation, the first of its kind in Spain. There are other 14C-dating laboratories in Spain, but they use traditional radiometric methods (radiation detectors). These methods are highly destructive (grams of carbon are required for the analysis), time-consuming (hours per sample) and less productive.
 
The use of Accelerator Mass Spectrometry allows:
 
-The reduction to the sub-milligram scale of the sample amount that is required for dating (almost non-destructive, which is really important in the analysis of valuable material).
-Sample measurements in less than one hour, producing a higher number of dating analyses per day than conventional methods (higher productivity). All these advantages are due to the fact that in the traditional procedures, the radiation emitted by 14C is measured, but with AMS, we measure the total number of 14C atoms that are contained in the sample.
 
During 2015 and 2016 we have continued with the previous planning, and the latest developments in the laboratory have been completely implemented. Thus, an automatic carbonate handling system has been set up, allowing the preparation of such samples in a simpler and faster way, and using the same graphitization line that is used for organic samples. This way the results can be easily compared even with different matrixes.
 
At this moment, the radiocarbon dating service counts with an important infrastructure: the Micadas (MIni CArbon DAting System) C-14 detection system, a graphitization line to reduce CO2 to graphite, an Elemental Analyzer to generate CO2 from organic samples, and the already mentioned carbonate handling system to generate CO2 from carbonate samples. At this moment we are developing the possibility of preparing dissolved inorganic carbon samples from liquids in this line.
 
lab c14
 

For radiocarbon measurements with accelerator mass spectrometry (AMS) at CNA solid graphite targets are required. Samples in the laboratory are therefore cleaned, and intrinsic carbon is extracted to be transformed in such material. In a general way, carbon is extracted as CO2 and is reduced to graphite with a graphitization system.

 

The Automated Graphitization Equipment (AGE) features a graphitization that is directly coupled to the sample combustion in an elemental analyzer (EA). AGE has been developed for fast and efficient sample preparations for radiocarbon measurement by means of accelerator mass spectrometry.

 

Traditionally, the cryogenic transport of CO2 into the graphitization reactors with liquid nitrogen is used after sample combustion. AGE uses instead a column filled with zeolite to trap the CO2 coming from the combustion in the EA. The CO2 can then be easily released by heating the zeolite trap and transferred to the reactor by gas expansion. The consequence of the AGE avoiding the use of liquid nitrogen is, that it is very compact and allows running fully automated for sample combustion and graphitization.

 

The new Carbonate Handling System (CHS) to obtain CO2 from carbonate samples is also coupled to AGE, but generates CO2 by acid dissolution instead of combustion. It uses an autosampler that purges the septum tubes in which the samples are stored, adds the acid, and transports the generated CO2 to the reactors.

 

The entire system with valves, ovens, temperature and pressure sensors is computer controlled. A LabVIEW program runs through all consecutive steps when processing a sample: catalyst preconditioning, sample combustion in the EA and CO2 trapping, thermal CO2 release from the trap into the reactor, and finally the graphitization reaction itself.