Carbon-14, questions on how it is created

[radagast]

This didn't work in 'How stuff works' so I'll try it here.

Some time back a friend (PhD Nuclear Engineer), told me that the energies a neutron needed to form C14 from nitrogen were (and this is where my memory gets real fuzzy) around 15 MEV. Furthermore that neither nuclear explosions or the Sun produced neutrons of this energy. The implications were they were formed in supernovas and survived due to relativistic time dialation.

This just seems to tickle my BS meter, but having no knowledge of nuclear physics, to speak of, I'd rather hear some confirmation of this before I go accepting it as likely or dismissing it.

 

[mmwave]

I think your BS meter may be working well. Carbon 14 dating works because a small fraction of the carbon dioxide we breathe is C14.

I believe the bulk of the C14 in the Earth's atmosphere is formed by cosmic rays hitting Nitrogen molecules in the Earth's atmosphere. When the Nitrogen atom decays it becomes carbon 14.

I don't have the chart of the nuclides with me to fill in the details but this is what I remember. If C14 weren't continuously created then the supply would be continuously decreasing and that would make carbon dating very difficult.

 

[jcsd]

15 MeV is tiny amount compared to some of the enegies of galatic cosmic rays.