Neutron energies at which C14 is produced

[radagast]

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.

 

[eagleone]

No you probably miss heard that. Eg. C14 forms from N14 and slow neutrons from secondary cosmic radiation in atmosphere, if you substitute this neutrons with neutrons of higher eng. You’ll get tritium from N14 (in atmosphere again :)...

Well,C14 is not the best survivor with it’s half time live of ~5730 :)...

p.s. Hope this data is correct after all I’m no n. physicist (although by may neighbor I’m nuclear biologist

 

[Greg Bernhardt]

First of all, let's clarify some terminology. "MEV" stands for "mega-electron volt," which is a unit of energy commonly used in nuclear and particle physics. It is equivalent to 1.602 x 10^-13 joules. So when your friend said that the energy needed to form C14 from nitrogen is around 15 MEV, what he probably meant is that the energy required for the nuclear reaction to occur is around 15 MeV.

Now, let's look at the actual nuclear reaction that produces C14 from nitrogen. This reaction is called "neutron capture," and it involves a nitrogen nucleus (with 7 protons and 7 neutrons) capturing a neutron to form a C14 nucleus (with 6 protons and 8 neutrons). This reaction can occur in nature, but it is quite rare. In order for this reaction to happen, the neutron must have a certain amount of energy, which is called the "neutron capture threshold energy." This energy is different for different nuclei, and for the nitrogen nucleus, the threshold energy is indeed around 15 MeV.

So, your friend is correct in saying that the energy needed for this reaction to occur is around 15 MeV. However, this does not necessarily mean that the neutrons needed for this reaction can only be produced in supernovas. In fact, neutrons can be produced in many different ways, including nuclear reactions in stars and nuclear reactors, as well as in cosmic ray interactions in the atmosphere. The Sun also produces neutrons, but they have much lower energies (around 0.025 MeV) and are not able to trigger the neutron capture reaction in nitrogen.

It is true that the survival of C14 in the atmosphere is related to relativistic time dilation, but this has more to do with the fact that C14 has a half-life of around 5,730 years. This means that after 5,730 years, half of the C14 in a sample will have decayed into nitrogen. However, due to relativistic time dilation, the half-life of C14 is slightly longer for objects that are moving at high speeds. This effect is very small, but it is enough to allow us to use C14 dating to determine the age of objects that are millions of years old.

So in summary, your friend is correct in saying that the energy needed for the neutron capture reaction to form C14 from nitrogen is around