Effective range of carbon dating
Cosmic rays are positively charged atoms moving at enormous speeds.When they strike ordinary atoms in the upper atmosphere, the cosmic rays smash them apart. Some of these neutrons then collide with nitrogen atoms.The terms "%Modern", or "pm C" and D14C are shown related in this diagram along with the Radiocarbon age in years BP (Before 1950 AD).If the reservoir corrected conventional radiocarbon age calculated is within the past 200 years, it should by convention be termed 'Modern' (Stuiver and Polach, 192).
Usually a proton is knocked out of the nitrogen atom's nucleus and is replaced with the neutron.
Another standard, Oxalic Acid II was prepared when stocks of HOx 1 began to dwindle.
The ratio of the activity of Oxalic acid II to 1 is 1.29330.001 (the weighted mean) (Mann, 1983).
A recent test by the British Science and Engineering Research Council has shown that the accuracy of the new technique is greatly overrated.
They found large variations in the radiocarbon 'dates' of objects of known age sent to 38 radiocarbon 'dating' laboratories around the world.