Leibniz laboratory for radiometric dating
The graphite is deposited on the iron powder introduced into a small quartz tube.
The reactor and iron powder are previously heated overnight at 90°C under continuous pumping.
Fe-C powder is pressed into a tablet which is used as a target in the sputter ion source of the accelerator.
The target is stored in argon atmosphere until the measurement.
For bones the collagen is extracted according to the modified Longin's method (see poster) After the chemical pretreatment the sample material in a quantity corresponding to ca.
1mg of carbon is placed into a quartz tube with copper dioxide (the source of oxygen needed for combustion) and silver wool (for the removal of gaseous sulphur and chlorine compounds). is reduced to graphite during the reaction with hydrogen at the temperature of 600-630°C (dependent on the reduction rate for a given sample) in the presence of iron as a catalyst.
Sample type and size Packing and sending of sample Pre-treatment procedures Conversion of sample carbon into graphite Hot samples A wide variety of organic samples (e.g.
* Sample size of dry peat; more material is required if the mineral content is high or the peat is decomposed. The precision of radiocarbon dates for recent samples (younger than 2000 years) of “normal” sample size (1-2 mg of carbon) is better than 0.5% (typically 0.3 - 0.4%) which equals /-40 years (25 - 30 years) for the 1-σ statistical uncertainty of the measured age.
Directly before the graphitisation the iron is oxidized and reduced in order to increase its catalytic properties.
Then COO is produced and continuously removed by freezing out in a mixture of dry ice and alcohol.
After subsequent magnetic and electrostatic analysis, the ions are identified in an ion detector.
The schematic layout of AMS spectrometer is presented below (adapted from Tuniz et al., 1998): Abbreviations used on the figure: IS1, IS2 - two ion sources used for different elements/applications or to increase the throughput L1-L6 - electrostatic or magnetic lenses ESA1, ESA2 - electrostatic analysers PA - pre-acceleration of ions M1, M2 - magnets AT-, AT - acceleration tubes for negative and positive ions, respectively HV - high-voltage terminal SC - stripping channel D - detector Compact Carbon AMS at Pozna Radiocarbon Laboratory, Poland (also in Polish).
Most commonly the AAA (acid-alkali-acid) method is used for organic samples like charcoal or organic remains.