All of these processes are carefully controlled at ORAU through our quality management system.
The unit uses some thirty different pre-treatment methods for samples of different kinds and in different states of preservation.
ratio might have varied over time, it was not until discrepancies began to accumulate between measured ages and known historical dates for artefacts that it became clear that a correction would need to be applied to radiocarbon ages to obtain calendar dates.
A general abbreviation, ambiguous if not understood from context, used for reporting dates obtained with any method is Before Present (BP), where "present" is 1950.
The study of tree rings led to the first such sequence: tree rings from individual pieces of wood show characteristic sequences of rings that vary in thickness because of environmental factors such as the amount of rainfall in a given year.