Radiocarbon (¹⁴C) – General principle

Resources of the earth such as oil, gas and coal with an age of several million years are always free of radioactive carbon. Living plants and animals, on the other hand, have an almost constant proportion of radioactive carbon in their biomass.
This is because, on the one hand, radioactive carbon is constantly decaying, but on the other hand, it is constantly being newly formed in the upper atmosphere and is therefore present everywhere as radioactive carbon dioxide. Through photosynthesis in the plants, this is subsequently also passed on to the animals.
The constant natural radioactivity of biomass on the one hand and the lack of radioactivity in fossil resources on the other makes it possible to distinguish between renewable and fossil resources and to quantify the proportions. Since the radioactive carbon only occurs with a proportion of 0.00000001 % in the carbon of the biomass, the measurement is still challenging today.

Our technology:

Liquid scintillation counting (LSC) is now the standard method for quantifying the radioactivity of low-energy radioisotopes of beta and alpha isotopes, and thus radioactive carbon: ¹⁴C.
The radioactive decay cannot be measured directly, but the measurement uses specific cocktails that convert the low energy of the decay into detectable light pulses. Usually, these specific cocktails consist of two basic components, i.e. an aromatic solvent (e.g. toluene) and a "scintillator" or special fluorine compounds "permafluorine".
The fluorine/scintillator molecules dissolved in the solvent absorb the energy released by the solvent and re-emit it (at a higher wavelength) as visible light with a wavelength around 420 nm.
The scintillators are preferably characterized by a fast decay time and a high fluorescence quantum yield.
The light is detected by the photomultipliers of the liquid scintillation counter and the events are recorded accordingly.
From these measurements, the corresponding natural decays per unit time are obtained.
A major problem in the measurement are always the external influences / disturbances, especially from cosmic rays, which create a background. To eliminate this, either a very thick shielding (lead) can be used (e.g. Quantulus) or the simultaneous measurement of this cosmic radiation by a third detector (Tricarb system, e.g. Hidex 300SL).

Both systems are routinely used by Agroisolab.

The test sample can rarely be measured directly. As a rule, the sample must be transferred to CO₂. As a procedure to convert the carbon present in the sample into CO₂, combustion is carried out in a special modified Makro-Element-Analyser. In detail, CO₂ gas is collected separately and interfering gases are separated. Using a temperature gradient, the CO₂ gas is released and absorbed in a cooled scintillation cocktail.
Still yet, the processing of the samples with the help of a special Marko-Element-Analyser is a unique selling point of Agroisolab, because with this procedure a very clean CO₂ gas can be obtained and furthermore transferred to the trapper in a very controlled manner. This guarantees optimal measurement quality of the sample and minimizes unwanted effects, e.g. quenching effect.

For sure, the entire application is accredited according to DIN EN ISO/IEC17025:2018