Posted: Aug 28, 2013 7:32 pm
Quite simply, it's possible to find Carbon-14 in coal, diamonds and oil, whenever these substances are in close proximity to other radionuclides. Such as the thorium and uranium isotopes found in granite, several of which have extremely long half-lives. Some of these isotopes can undergo spontaneous fission, and release neutrons. When this happens, carbon atoms in the adjacent coal, oil or diamonds can absorb those neutrons. Carbon-12 absorbs one neutron to become Carbon-13, which is still stable, but can then absorb a second neutron from these sources, to become Carbon-14. When you have a sufficient abundance of neutron-releasing isotopes in the adjacent strata, coal, oil and diamonds can continue absorbing neutrons, and the amount of Carbon-14, though small, remains measurable as long as new Carbon-14 atoms are being produced by neutron absorption.
There's also the possibility of other particle interactions producing the same end result. Whilst cosmic ray spallation of nitrogen nuclei in the atmosphere is a large source of terrestrial Carbon-14, it's also possible for spallation events to convert nitrogen atoms in coal or oil (there are usually a fair number present, courtesy of the fact that the living organisms from which the coal and oil were derived also contained lots of nitrogen atoms).
There's also the possibility of other particle interactions producing the same end result. Whilst cosmic ray spallation of nitrogen nuclei in the atmosphere is a large source of terrestrial Carbon-14, it's also possible for spallation events to convert nitrogen atoms in coal or oil (there are usually a fair number present, courtesy of the fact that the living organisms from which the coal and oil were derived also contained lots of nitrogen atoms).