Age range of radiocarbon dating
They are Stuiver and Polach (1977) define a radiocarbon date to include five things: (a) the use of the 5,568-year half-life (mean life 8,033 years); (b) the assumption of constancy of 14C atmospheric level during the past; (c) direct or indirect comparison to a known standard, oxalic acid; (d) isotopic fractionation normalization of all sample activities to the base of δ13C = −25 ‰; and (e) the year 1950 which is automatically the base year, with ages given in years BP (i.e., where present is defined as AD 1950).This is a very specific set of criteria for publishing conventional radiocarbon ages.When the lab performs the radiocarbon measurements, it is getting just that one measurement, which is the ratio of the C-14 content to the C-12 content.This C-14 content level is measured and reported with one standard deviation.If nobody else, Jull and Hodgins should be able to confirm the details of the tests run.Here is what I’ve been able to determine (or guess) from Krosney, however, who gives the most detailed account that is available to me right now. Christian Askeland has given us a blog post update at Evangelical Textual Criticism, including this exciting quote from that blog post: “The National Geographic Society granted the Arizona AMS laboratory permission to send me the actual results, and I am publishing an update on the dating of the Tchacos Codex based on the findings.” Also, “The lab had six test results.”] Krosney’s Account The raw data (such as it is) is reflected in the account presented by Krosney on pp.To run roughshod over the science (forgive me if I have misrepresented it somehow) of radiocarbon dating very quickly, there are two isotopes of Carbon in the sample that are measured: C-14 and C-12.The C-14 is an unstable isotope, while the C-12 is a stable isotope.
The reason for my confidence here is not simply due to the reference to “radiocarbon years,” which already indicates as much.It is then converted into a “radiocarbon date” (equivalently, “radiocarbon age” and “radiocarbon years” BP) according to the conventions described above.The Wikipedia page on Radiocarbon dating actually seems to be fairly good and goes over some of the potential pitfalls involved in radiocarbon dating.The very specific band of /- margins of error mentioned, all between 47 and 58 years on each side, correspond result of a C-14 test and, specifically, to the 1-sigma confidence level that is used to express radiocarbon age results. Jull, “Accelerator radiocarbon dating of art, textiles, and artifacts,” in Nuclear News (June 1998).For such figures, we should expect a figure between 40 and 60 years on each side, as Jull’s own publication record bears out: “The AMS method has generally improved since its inception, so that external precision of about ±0.5 percent in 14C content, or ±40 years in uncalibrated radiocarbon age are possible on 1-mg-sized samples.” “For radiocarbon ages, errors of about ±50 years on recent material are typical for accelerator measurements.” – A. The use of /- expressions (“plus or minus”) is also consistent with the idea that we are seeing (uncalibrated) “radiocarbon years” here.