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The Reactions The Main Sequence – The P – P Chain

The Reactions The Main Sequence – The P – P Chain. 1 H + 1 H  2 H + proton + neutrino. 2 H + 1 H  3 He + energy. 3 He + 3 He  4 H + 1 H + 1 H + energy. The net result -. 4 ( 1 H )  4 He + energy + 2 neutrinos. The Reactions The Main Sequence – The CNO Cycle

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The Reactions The Main Sequence – The P – P Chain

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  1. The Reactions The Main Sequence – The P – P Chain 1H + 1H 2H + proton + neutrino 2H + 1H 3He + energy 3He + 3He 4H + 1H + 1H + energy The net result - 4 ( 1H ) 4He + energy + 2 neutrinos

  2. The Reactions The Main Sequence – The CNO Cycle M > 1.2 Mסּ and T > 17 million K More massive stars burn hydrogen via a catalytic reaction called The CNO CYCLE. Because the initial step in the CNO Cycle requires a Carbon nucleus (6 p+) to react with a proton it requires higher temperatures and is much more temperature sensitive than the P-P Chain (The energy produced is proportional to T20 for the CNO cycle vsT4 for the P-P Chain). Stars of mass greater than about 1.2 M with core temperatures, Tcore > 17 million K, produce most of their energy by the CNO cycle. 12C + 1H 13N 13N 13C (unstable radioactive decay) 15N + 1H 12C + 42He 13C + 1H 14N 15O 15N (unstable radioactive decay) 14N + 1H 15O

  3. The Reactions Both the p – p chain and the CNO cycle produce Helium

  4. The Reactions The Triple Alpha Process T > 100 million K 3 ( 4He ) 12C

  5. Advanced Nuclear Reaction Stages 12C + 4He 16O

  6. Advanced Nuclear Reaction Stages What’s next * “Common” Element Fusion * Helium Capture

  7. Advanced Nuclear Reaction Stages T > 500 million K Carbon Fusion to Magnesium 12C + 12C 24Mg

  8. Advanced Nuclear Reaction Stages T > 1 billion K Oxygen Fusion to Sulfur 16O + 16O 32S

  9. Advanced Nuclear Reaction Stages What’s next * “Common” Element Fusion * Helium Capture Notice from Previous slides: “Common Element Fusion” requires VERY high temperatures

  10. Advanced Nuclear Reaction Stages What’s next * “Common” Element Fusion * Helium Capture Since “Common Element Fusion” requires VERY high temperatures, Helium capture is much more probable in the core of a star

  11. Advanced Nuclear Reaction Stages Helium Capture to form Oxygen, Neon, Magnesium and Silicon 12C + 4He 16O 16O + 4He 20Ne 20Ne + 4He 24Mg 24Mg + 4He 28Si

  12. Advanced Nuclear Reaction Stages Silicon can be broken apart by the high energy photons in the core (photodisintegration). Photon +28Si  7 (4He) The Helium produced in the photodisintegration of Silicon drive further reactions

  13. Advanced Nuclear Reaction Stages Helium Capture to form Sulfur, Argon, Calcium and Titanium 28Si + 4He 32S 32S + 4He 36Ar 36Ar + 4He 40Ca 40Ca + 4He 44Ti

  14. Advanced Nuclear Reaction Stages Helium Capture to form Chromium, Iron and Nickel (unstable to and isotope of Cobalt and then to an isotope of Iron) 44Ti + 4He 48Cr 48Cr + 4He 52Fe 52Fe + 4He 56Ni 56Ni →56Co 56Fe

  15. Advanced Nuclear Reaction Stages T > 3 billion K Each reaction produces a nucleus with two more protons. As a result, elements with an even number of protons are produced. However, there are enough free protons in the core that single proton capture can occur as well. Although not as probable as the previous reactions, proton capture will produce elements with an odd number of protons.

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