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The reaction: 15 8O → 15 7N + e+ + ν e + 2.75 MeV (half-life of 122.24 seconds)
appears twice with yields of 2.75 and 1.73 mev yield, but are otherwise identical. Which, or (my physics is weak) both?
"The CNO cycle may also be the dominant source of nitrogen and oxygen production"
Er, how? It doesn't create a net increase in the number of N or O nuclei. -- Bth
There is an equilibrium concentration N and O available in stars. When stars cool down, this can form N2 and O2. In heavier stars, when hydrogen/helium is depleted CNO starts reacting with other CNO molecules to form silicium (and slightly heavier components).
Is it a convention to write anenergy yield, so the liberation of energy, in the positive form ? This is contrary to chemical convention. Sikkema 14:23, 2 October 2007 (UTC)
Hi i have a little question that you may just be able to help me with well here it goes... What type of radioactive particle was emitted by 13/7N and 15/7N? your help is much appriciated thank you
- 13N-> beta+ + 13C (no gamma) 15N stable, abundance 0.366%
The link below point to the paper of Hans Bethe in which he introduces the CNO cycle.
http://prola.aps.org/abstract/PR/v55/i5/p434_1
The german wiki calls it Bethe-Weizsäcker process is this also a name for it?-- Stone 11:27, 30 June 2006 (UTC)
Out of interest, can anyone provide more information on where the elements in the CNO cycle come from? There doesn't appear to be any mechanism given in this article on how they're initially generated, and they aren't featured in the p-p chain. Do they then come from the triple alpha process? Thanks in advance -- Xanthine 21:35, 29 July 2007 (UTC)
Why are the isotopes of C, O, N in equations not given with mass number? This is most unhelpful as it is now. Asgrrr ( talk) 08:25, 13 April 2009 (UTC)
Changed the CNO-I passage to show mass numbers. It may not be as visually pleasing, but this is the information that needs to be shown. If physiformulae can't do that then it needs to be discarded. Asgrrr ( talk) 13:51, 13 April 2009 (UTC)
"The presence of the heavier elements carbon, nitrogen and oxygen places an upward bound on the maximum size of massive stars to approximately 150 solar masses." This sounds like a very interesting statement. Could someone with the required knowledge add a sentence or two to expand on how the presence of CNO creates an upper bound? -- Gargletheape ( talk) 19:39, 12 August 2009 (UTC)
Will the graph on this page suffice as a reference for the threshold temperature of the CNO cycle? Gizmoguy ( talk) 19:11, 2 April 2011 (UTC)
Tonight I added all the hot CNO reactions as well. I weighed creating a new page rather than adding to this one, but the hot CNO cycle also can use all of the cold CNO reactions, so I decided it made more sense to expand this article instead. But to start with, I just added the reactions and small blurbs for the new sections of Cold and Hot CNO. So some of the introduction material needs to be moved down to the Cold section when it does not apply to the Hot cycles. There is also not yet much information on the Hot CNO cycles. Overall I also think we need some more historical discussions, since originally only the CN cycle was known. A more firm discussion of limiting reactions enters us into the ideas of the later discovered CNO-II, and then CNO-III and CNO-IV networks. And once we get into discussion of limiting reactions, this can feed really nicely into the Hot CNO, where the limiting reactions are different! Happy editing. DAID ( talk) 02:30, 15 August 2011 (UTC)
"The neutrinos escape from the star carrying away some energy." This is classical weasel-wording. There should be a statement about the actual amount of energy carried away by Neutrinos. According to Scheffler & Elsässer, 1990, "Physik der Sterne und der Sonne" (physics of the stars and the Sun) it is about 1.7 MeV for CNO-I (I have added the reference there). The book does not give any information about the neutrino energies in the other beta decay reactions.-- SiriusB ( talk) 20:48, 24 August 2011 (UTC)
Reading through the article I noticed (what appears to be) extraneous text under HCNO-III; as I do not know the purpose behind the text, I have left it alone within the article for someone knowledgeable of this topic to correct:
"...(half-life of 17.22 seconds) **[There was a typo here -- the half-life was listed as 122.24 s, the half-life for oxygen-15; what is the energy output of this particular decay?]"
Cheers -Ham Radio 03:14, 24 February 2012 (UTC) — Preceding
unsigned comment added by
Ke5skw (
talk •
contribs)
Article says:
13_7 N → 13_6 C + e+ + ν_e + 1.20 MeV (half-life of 9.965 minutes)
But An Introduction to Nuclear Astrophysics By Richard N. Boyd (2008) gives 2.220 MeV for this reaction. Same number in [1]; Nitrogen-13 (ref= Phillips, A.C. (1994). The Physics of Stars. John Wiley & Sons. ISBN 0-471-94057-7.) ` a5b ( talk) 23:35, 8 January 2013 (UTC) PS: This was changed in diff. ` a5b ( talk) 23:39, 8 January 2013 (UTC)
The lede has, from my viewpoint, two issues:1) Temperature is discussed independently from pressure (density?). I know that both are important for any nuclear chain reaction, so unless pressure (range) is unique for any given Temperature, regardless of the mass of the star (!), then this discussion is just plain inadequate (and misleading). 2) The CNO Cycle is claimed to be both a single thing and yet there are 7 different CNO cycles listed. This makes no sense. There is almost no discussion of when these different mechanisms occur (under what conditions (T, P, and composition)) (or when each peaks, both in absolute terms and in relative terms). 3) One last minor thing: isn't metallicity of the star also important in determining the fusion processes? If so, then that should be mentioned. Clearly it's not just mass, temperature and pressure of a star: metallicity and location (distance from center) are also important (I know they're interrelated). Abitslow ( talk) 16:53, 18 June 2016 (UTC)
The CNO graphic by Antonio Ciccolella has an error. The Alpha particle emitted should be 4He, not 2He. — Preceding unsigned comment added by 73.17.21.109 ( talk) 19:22, 2 September 2018 (UTC)
I may not be a physicist (or even know the first thing about physics or chemistry or science), but shouldn't a claim this specific have some documented support?
"The Sun has a core temperature of around 15.7×106 K, and only 1.7% of 4 He nuclei produced in the Sun are born in the CNO cycle." Briandrewdrew ( talk) 08:28, 3 October 2020 (UTC)
Not much else to add, really;
First Direct Experimental Evidence of CNO neutrinos Borexino Collaboration (2020) https://arxiv.org/pdf/2006.15115.pdf — Preceding unsigned comment added by Ianw16 ( talk • contribs) 04:56, 27 November 2020 (UTC)
When the nucleus becomes nitrogen-15, do we really want to continue the cycle on to oxygen-16 and back to oxygen-17? Nitrogen-15 is back in a stage of the basic CNO cycle (CNO-I) and will follow that the vast majority of the time.
A similar question could be asked with CNO-IV. Johnm307 ( talk) 16:47, 21 December 2020 (UTC)