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In the CNO cycle, how does Nitrogen-15 become Carbon-12 and Helium-4?

  1. Nov 9, 2014 #1
    1. The problem statement, all variables and given/known data
    I understand the rest of the cycle, the way my textbook has it, which is:
    12C→13N→13C→14N→15O→15N→12C+4He

    The portion in bold is what I don't understand.
    2. Relevant equations


    3. The attempt at a solution
    I do understand that when the mass number increases (like from Carbon-13 to Nitrogen-14), that a hydrogen nucleus is fused(?) together with the Carbon-12 nucleus, and the Nitrogen-14 nucleus and energy (in the form of gamma rays?) are emitted. What I don't understand is how Nitrogen-15 can decay(?) into Carbon-12 and a Helium-4 nucleus.

    I was thinking that this was a form of alpha decay, the emitting of the Helium nucleus. However, if that is the case, I don't see how Carbon-12 is also formed.

    Any help is appreciated, thanks :)

    Sorry if what I wrote down is hard to follow.
     
  2. jcsd
  3. Nov 9, 2014 #2

    SteamKing

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    There are several different CNO cycles which occur in stars of different masses. The various products in the CNO reaction chain occur at different times due to the fusion of a proton with a C or N nucleus, which then decays radioactively in one of several different ways. For more details on the various CNO cycles, see this article:

    http://en.wikipedia.org/wiki/CNO_cycle
     
  4. Nov 10, 2014 #3

    Orodruin

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    It is not a decay. It is a process involving an extra proton which is not visible since you did not write out the additional protons needed in any of the reactions.
     
  5. Nov 10, 2014 #4

    SteamKing

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    I think if you review the attached article in Post #2, you will see that some of the steps in the CNO cycles occur due to the spontaneous emission of positrons from unstable nuclei produced after fusion with a proton. This process occurs over a period of time (i.e., there is a measurable half-life associated with it), and it fits with the definition of radioactive decay as it is understood in non-stellar processes:

    http://en.wikipedia.org/wiki/Radioactive_decay

    I believe I clearly stated that this process is initiated after the various nuclei fuse with a proton, but in the interest of brevity, I chose not to reproduce the details of all of the reactions and instead referred the OP to the attached article in Post #2 for the details.
     
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