QUALITY ASSURANCE

To ensure that the radiocarbon measurements from Stonehenge can be converted into absolute dates, it is necessary to demonstrate that they are accurate within the precision quoted. Both laboratories maintain continual programmes of quality assurance procedures, in addition to participation in international intercomparison studies (Otlet et al 1980; International Study Group 1982; Scott et al 1990; Rozanski et al 1992; Scott et al forthcoming), and the use of Oxalic II acid (Stuiver 1983) as a primary standard.

The measurements produced for the Third International Radiocarbon Intercomparison on material which was also used as secondary standards for the Stonehenge samples are:

TIRI B (3929-3200 BC) consensus mean=4485BP consensus median=4500BP

4523+/-17BP (Belfast); 4510+/-35BP (Oxford); 4525+/-12BP (Pearson et al 1986).

TIRI D (unknown) consensus mean=3799BP consensus median=3805BP

3845+/-22BP (Belfast); 3885+/-35BP (Oxford). It should be noted that the interpretation of the TIRI results for this sample is complicated by questions of homogeneity and sample preparation (see Scott et al forthcoming).

The approach to quality assurance adopted here allows the direct comparision of results on known-age wood measured along with the Stonehenge samples with the results produced as part of the 1986 calibration.

The measurements relevant to each of the Stonehenge samples in the new series are:

Measurements are also available for GU-5109, measured at the Scottish Universities Research and Reactor Centre in 1991:
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