Radiocarbon 14C Dating
Beginning in September 2008, Sturt Manning of the Cornell Tree-Ring Laboratory directed a project that tested numerous conifer wood samples of known tree-ring age for their radiocarbon age. The project employed a rigorous double-blind procedure designed to eliminate any subjective unrecognized biases of the individuals engaged in the project.
As in standard double-blind practice, the procedure introduced an independent agent between the Cornell Lab that provided the wood samples and the radiocarbon labs - VERA, ORAU, and Beta Analytic (see below) - charged with dating them. The independent agent received labeled samples from Cornell and scrambled the labels before the samples were sent off for radiocarbon dating. That is, the original labels were redistributed among the samples and the document that recorded the relabeling was sealed and secured. Consequently, the radiocarbon labs were unaware of the known tree-ring age of the samples sent to them for testing. Likewise, Manning at the Cornell lab was in the dark concerning the distribution of the raw results reported by the radiocarbon labs. The linkage of the raw radiocarbon lab data to the known age of the samples could only be ascertained with the unsealing of the double-blind document.
In the original research, done in the 1940’s, the radiocarbon method of age determination was found to have furnished approximate results: the tolerances ranged from ±150 to ±450 years (Arnold and Libby, 1949). Since the dates of the Egyptian pharaohs determined by the radiocarbon method matched the expected dates well enough, Arnold and Libby concluded that ”the two basic assumptions of the radiocarbon age determination method – namely, the constancy of the cosmic radiation intensity and the possibility of obtaining unaltered samples – are probably justified for wood up to 4600 years”.
Arnold and Libby’s two basic assumptions, however, are incompatible with the highly precise results researchers aim to realize nowadays. Modern analysis of raw 14C data corrects for variations in the cosmic ray flux and other factors affecting the concentration of 14C in the atmosphere. Further, the availability of unaltered samples appears unrealistic, since extraneous inclusions often contaminate the samples and they must be treated prior to testing.
The draft article: Sturt Manning, 2012.
Manning's Cornell test served as a trial run of the double-blind procedure intended to resolve the inconsistencies of earlier research. The method proved workable and can be employed in future tests.
The Cornell Lab used the IntCal09 calibration curve to translate the raw 14C data of the conifer samples to calendar dates. The results support the reliability of IntCal09 over the range of dates tested. In the course of the experiment, however, questions arose regarding the pretreatment of the conifer samples. The matter has not yet been resolved.
Manning, Sturt, 2012 Random Snapshot on Radiocarbon Laboratory Dating Accuracy from a small Double Blind Test on Known Age Conifer Samples (and an issue regarding pretreatment)
Arnold and Libby, 1949 Age Determinations by Radiocarbon Content: Checks with Samples of Known Age
Vienna Environmental Research Accelerator (VERA)
Oxford Radiocarbon Accelerator Unit (ORAU)
Beta Analytic Radiocarbon Dating
Cornell Tree-Ring Laboratory