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  1. en.wikipedia.org › wiki › CNO_cycleCNO cycle - Wikipedia

    In the CNO cycle, four protons fuse, using carbon, nitrogen, and oxygen isotopes as catalysts, each of which is consumed at one step of the CNO cycle, but re-generated in a later step. The end product is one alpha particle (a stable helium nucleus), two positrons, and two electron neutrinos. There are various alternative paths and catalysts involved in the CNO cycles, all these cycles have the same net result: 4 1 1 H + 2 e − → 4 2 He + 2 e +

  2. Die Namen CN- beziehungsweise CNO-Zyklus leiten sich von den an der Reaktion beteiligten Elementen Kohlenstoff (C), Stickstoff (N) und Sauerstoff (O) ab. Während die Proton-Proton-Reaktion eine wichtigere Rolle bei Sternen mit Größen bis knapp über die Masse der Sonne spielt, zeigen theoretische Modelle, dass der Bethe-Weizsäcker-Zyklus vermutlich die vorherrschende Energiequelle in schwereren Sternen mit etwas mehr als der Sonnenmasse und in allen Riesensternen darstellt.

    • History of The Theory
    • The proton–proton Chain
    • The Pep Reaction
    • See Also

    The theory that proton–proton reactions are the basic principle by which the Sun and other stars burn was advocated by Arthur Eddington in the 1920s. At the time, the temperature of the Sun was considered to be too low to overcome the Coulomb barrier. After the development of quantum mechanics, it was discovered that tunneling of the wavefunctions ...

    The first step in all the branches is the fusion of two protons into a deuteron. As the protons fuse, one of them undergoes beta plus decay, converting into a neutron by emitting a positron and an electron neutrino(though a small amount of deuterium nuclei is produced by the "pep" reaction, see below): The positron will annihilate with an electron ...

    A deuteron can also be produced by the rare pep (proton–electron–proton) reaction (electron capture): In the Sun, the frequency ratio of the pep reaction versus the p–p reaction is 1:400. However, the neutrinos released by the pep reaction are far more energetic: while neutrinos produced in the first step of the p–p reaction range in energy up to 0...

    • History
    • Key Reactions
    • Reaction Rate
    • Further Reading
    • External Links

    In 1920, Arthur Eddington, on the basis of the precise measurements of atomic masses by F.W. Aston and a preliminary suggestion by Jean Perrin, proposed that stars obtained their energy from nuclear fusion of hydrogen to form helium and raised the possibility that the heavier elements are produced in stars. This was a preliminary step toward the id...

    The most important reactions in stellar nucleosynthesis: 1. Hydrogen fusion: 1.1. Deuterium fusion 1.2. The proton–proton chain 1.3. The carbon–nitrogen–oxygen cycle 2. Helium fusion: 2.1. The triple-alpha process 2.2. The alpha process 3. Fusion of heavier elements: 3.1. Lithium burning: a process found most commonly in brown dwarfs 3.2. Carbon-bu...

    The reaction rate density between species A and B, having number densities nA,B, is given by: 1. 1.1. r = n A n B k {\\displaystyle r=n_{A}\\,n_{B}\\,k} where k is the reaction rate constant of each single elementary binary reaction composing the nuclear fusionprocess: 1. 1.1. k = ⟨ σ ( v ) v ⟩ {\\displaystyle k=\\langle \\sigma (v)\\,v\\rangle } here, σ(v...

    Bethe, H. A. (1939). "Energy Production in Stars". Physical Review. 55 (1): 541–7. Bibcode:1939PhRv...55..103B. doi:10.1103/PhysRev.55.103. PMID 17835673.
    Bethe, H. A. (1939). "Energy Production in Stars". Physical Review. 55 (5): 434–456. Bibcode:1939PhRv...55..434B. doi:10.1103/PhysRev.55.434. PMID 17835673.
    Hoyle, F. (1954). "On Nuclear Reactions occurring in very hot stars: Synthesis of elements from carbon to nickel". Astrophysical Journal Supplement. 1: 121–146. Bibcode:1954ApJS....1..121H. doi:10....
    Clayton, Donald D. (1968). Principles of Stellar Evolution and Nucleosynthesis. New York: McGraw-Hill.
    "How the Sun Shines", by John N. Bahcall(Nobel prize site, accessed 6 January 2020)
    Nucleosynthesis in NASA's Cosmicopia
    • Cycle Principal : CNO - I
    • Cycles Secondaires
    • Conséquences en Astrophysique
    • Voir aussi
    • Liens Externes

    En réalité, il n'y a pas un, mais trois cycles qui sont importants d'un point de vue astrophysique. Le cycle principal est le suivant[2]: Ce cycle a pour résultat la fusion, par capture de protons, de quatre noyaux d'hydrogène (1H, ou protons) en un seul noyau d'hélium (4He, ou particule alpha), et fournit de l'énergie en concordance avec l'équatio...

    À la dernière étape de ce cycle principal, là où le dernier proton absorbé par le noyau de 15N permet de restaurer le noyau de 12C initial, il existe une autre voie : celle de la création d'un noyau de 16O accompagnée d'une émission γ). Cette autre voie arrive avec une probabilité de 0,04 % (soit 1 fois sur 2500), le bilan n'est alors plus une prod...

    Bien que le nombre total de noyaux « catalytiques » soit conservé dans le cycle, durant la séquence principale les proportions relatives des noyaux sont changées. Quand le cycle parvient à l'équilibre, le rapport des noyaux 12C/13C est porté à 3,5 et 14Ndevient le noyau majoritaire, indépendamment de la composition initiale. Pendant les dernières é...

    Bibliographie

    : document utilisé comme source pour la rédaction de cet article. 1. [Sacco 2020] Laurent Sacco, « Des neutrinos du cycle CNO du Soleil ont enfin été observés ! », Futura,‎ 25 juin 2020 (lire en ligne).

    Articles connexes

    1. Chaîne proton-proton 2. Réaction triple alpha

  3. Sometimes C and N are considered alpha process elements since, like O, they are synthesized in nuclear alpha-capture reactions, but their status is ambiguous: Each of the three elements is produced (and consumed) by the CNO cycle, which can proceed at temperatures far lower than those where the alpha process starts producing significant amounts …

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