The usefulness of radiocarbon dating is limited
Fluctuations in the amount of carbon dioxide in the atmosphere can also affect the concentration of . 2, which shows the increasingly large difference between radiocarbon and true age from 7000 to 15000 years BP.
This deviation is much smaller less than 7000 years ago.
Carbon-14 is produced in the upper atmosphere by nuclear reactions induced by cosmic rays on nitrogen (see Fig. Nearly all the carbon in the atmosphere is present as carbon dioxide (CO in the atmosphere maintains an equilibrium with the biosphere and the oceans.
Because plants absorb carbon from the atmosphere during photosynthesis, and as animals eat plants, the animals will also contain the same level of C in a sample with that in "modern" material, defined as 1950 AD.
Accelerator mass spectrometry (AMS) is a technique for direct measurement of the concentration of radioisotopes.
A radiocarbon measurement can be obtained on a sample of ~0.5 mg of carbon, and measured to 40 years in uncalibrated radiocarbon age in a measurement time of 3040 minutes on each sample.
This article is reproduced from Nuclear News, June 19998, and is based on a paper presented at the ANS Winter Meeting, held November 16-20, 1997, in Albuquerquete N. AMS has become an accurate and precise method for dating many types of materials - including such interesting items as the Shroud of Turin and the Dead Sea Scrolls, which will be discussed laterwhere only a small sample can be spared.For historical reasons, uncalibrated radiocarbon measurements are often referred to a half-life of 5568 years.However, this inconsistency is corrected during calibration [the reason for using the (Willard F.) Libby half-life of 5568 years instead of the correct one of 5730 years has to do with the finding in about 1962 that the true half-life was 573030 years.We can equally well use a different standard if we know its relation to "modern," or 1950 AD.Radiocarbon ages are then quoted as "years before present" (BP).