Nitrogen production in stellar nucleosynthesis?

[bbbl67]

So once a star enters the helium fusion stage, it uses the Triple-alpha process to create Carbon from Helium. It then uses the Alpha Ladder process to create Oxygen from Carbon. So my question is, how is Nitrogen, in between Carbon and Oxygen, produced? All I can think of is that either Oxygen decays down to Nitrogen, or Carbon decays up to Nitrogen. If nitrogen is indeed produced through just decays, is this a large enough process to produce the amount of nitrogen we see all around us (70% of Earth's atmosphere)?

Also how are all of the stuff between Helium and Carbon produced, such Lithium, Beryllium, & Boron? Some Lithium might have been produced somewhat in Big Bang nucleosynthesis, but not all?

 

[mfb]

Nitrogen is rare compared to carbon and oxygen. It is a factor 5-10 less common in our galaxy.
It is produced in the CNO cycle but also via photodisintegration and beta decays.

Most lithium is still from the big bang, the other light nuclides are products from cosmic rays or side-reactions in fusion processes.

 

[phyzguy]

Look at this graph of elemental abundances in the solar system. Note it is a log scale, so you can see how much rarer Li, Be, and B are than heavier elements. You can also see the alternating pattern caused by what you called the Alpha Ladder.

 

[bbbl67]

Nitrogen is rare compared to carbon and oxygen. It is a factor 5-10 less common in our galaxy.
It is produced in the CNO cycle but also via photodisintegration and beta decays.

Most lithium is still from the big bang, the other light nuclides are products from cosmic rays or side-reactions in fusion processes.

I thought in the CNO cycle no new carbon, nitrogen or oxygen are produced? Any pre-existing CNO is used as a catalyst during the reactions, but immediately returned intact after the reaction is done. Also if Nitrogen is so rare, why is it such a dominant part of our atmosphere?

 

[phyzguy]

I thought in the CNO cycle no new carbon, nitrogen or oxygen are produced? Any pre-existing CNO is used as a catalyst during the reactions, but immediately returned intact after the reaction is done. Also if Nitrogen is so rare, why is it such a dominant part of our atmosphere?

As you see in the CNO cycle, N is produced by proton capture from C. If there is no N to begin with, it will build up until the rate of destruction in the CNO cycle equals the rate of production. So there will be an equilibrium concentration. Also, as you see in the graph I uploaded, N is not that rare. The reason it builds up in the atmosphere is that it is relatively unreactive. The total mass of N in the Earth's atmosphere is tiny compared to the mass of elements such as C in the solid mass of the Earth.