Leibniz laboratory for radiometric dating
The relative numbers of the atoms of different carbon isotopes in the sample are directly measured and the radiocarbon age is determined.A system for the preparation of samples for AMS dating has been developed in the Gliwice Radiocarbon Laboratory in 1999.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.Approximate sample sizes required for the AMS Please contact us before sending these samples.* 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.
Subsquently, low-energy mass analysis is performed with the use of magnets and sometimes also electrostatic analysers.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.Identifiable samples (macrofossils) with high carbon contents are preferred over sediments and soils.For high precision we recommend at least 1 mg of carbon after chemical preparation (see: Pre-treatment procedures).