Axel Steinhof, Dr.
Phone: +49 (0)3641 57 - 6450
Fax: +49 (0)3641 57 - 7450
Measurements of 14C-isotope ratios
The 14C analytics group supports scientists with measurements of the 14C isotope ratios in soil, sediment, wood, water, and air samples. Measuring 14C in natural samples is rather sophisticated since the 14C/C ratio is extremely low, even in recent samples it is in the range of 10-12.The measurements are carried out with the method accelerator mass spectrometry (AMS). In our lab we use the instrument MICADAS of the company Ionplus (Dietikon, Switzerland).
AMS allows the measurement of small sample quantities; the usual sample quantity is 0.5 mg carbon. With an adapted chemical preparation the carbon is extracted from the various samples and converted into graphite. (The respective sample preparation method may require larger sample quantities than 0.5 mg C.) This graphite is ionized in the AMS system (negative charge) and accelerated with the help of electrical fields to a final energy of 400 keV. The AMS system also acts as a filter for other unwanted ions (background), so that individual 14C ions can be counted at the end of the apparatus and, together with the 12C and 13C current measurements, the 14C isotope ratios can be determined. If there are free capacities for sample preparation and AMS measurements external samples can also be analyzed. To protect cultural heritage, we have joined an initiative of ETH Zurich and date only samples that comply with these guidelines.