CNO cycle

The CNO (carbon-nitrogen-oxygen) cycle

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is one of two fusion reactions by which stars convert hydrogen to helium, the other being the proton-proton chain.

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While the proton-proton chain is more important in stars the size of the sun or less, theoretical models show that the CNO cycle is the dominant source of energy in heavier stars. The CNO process was proposed in 1938 by Hans Bethe.

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The reactions of the CNO cycle are:

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12C + 1H → 13N + γ +1,95 MeV

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13N → 13C + e+ + νe +1,37 MeV

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13C + 1H → 14N + γ +7,54 MeV

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14N + 1H → 15O + γ +7,35 MeV

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15O → 15N + e+ + νe +1,86 MeV

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15N + 1H → 12C + 4He +4,96 MeV

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The net result of the cycle is to fuse four protons into an alpha particle plus two positrons and two neutrinos, releasing energy in the form of gamma rays. The carbon, oxygen, and nitrogen nuclei serve as catalysts and are regenerated.

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In a minor branch of the reaction, occurring just 0.04% of the time, the final reaction shown above does not produce 12C and 4He, but instead produces 16O and a photon and continues as follows:

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15N + 1H → 16O + γ

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16O + 1H → 17F + γ

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17F→ 17O + e+ + νe

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17O + 1H → 14N + 4He

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Like the carbon, nitrogen, and oxygen involved in the main branch, the fluorine produced in the minor branch is merely catalytic and at steady state, does not accumulate in the star.

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Carbon: :Alternative meaning: Carbon (API)...

Nitrogen: Nitrogen is the chemical element in the periodic table that has the symbol N and atomic number 7. A common normally colorless, odorless, tasteless and mostly inert diatomic non-metal gas, nitrogen constitutes 78 percent of Earth's atmosphere and is a constituent of all living tissues. Nitrogen forms...

Oxygen: :This article is about the chemical element oxygen. For other usage, see Oxygen (disambiguation)....

CNO cycle related Images and Photos (experimental)

Cycle	SUNDAY CYCLE	Naphta Cycle	Cycle of Life
Cycle and Bud	Cycle and Bud	Cycle World BMW R75 750	Cycle Savages 1970
Neon Spin Cycle	Cycle World BSA Spitfire MKIII Poster	The Moscow Cycle Works c.1930	Pendulum Half Cycle