Leibniz laboratory for radiometric dating 10 dating mistakes
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.Most commonly the AAA (acid-alkali-acid) method is used for organic samples like charcoal or organic remains.Shells are cleaned and the outer part is dissolved in a weak acid.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.Identifiable samples (macrofossils) with high carbon contents are preferred over sediments and soils.
charcoal, seeds, leaves, wood, and sediments), carbonates, and bones can be dated.
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.
Prepared graphite targets are sent to an AMS laboratory for the measurement (at present to Pozna Radiocarbon Laboratory, Poland or to Leibniz Laboratory for Radiometric Dating and Isotope Research in Kiel, Germany).
Each batch of samples is accompanied by at least two modern standard (Oxalic Acid) and two background (coal or marble containing no radioactive carbon) samples, prepared in the same way as samples of unknown age which are used for the age calculation.
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The AMS technique is an extension of conventional isotope ratio mass spectrometry in which a magnetic field is used to separate the ionised carbon isotopes by their different masses which are quantified separately.