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physical phenomena > energy source > exothermic fusion process > hydrogen burning > proton-proton chain

proton-proton chain (p-p chain)
subject			fact

proton-proton chain	has required reactant concentration high
	has optimum temperature 5 million Kelvin
	has part intermediate product deuterium
	has part intermediate product tritium
	has part product helium
	has part reactant proton
	has next higher temperature reaction carbon cycle
	has temperature dependence E ∝ T4
	has minimum temperature 107 K
	has synonym p-p chain
	has location the center of the Sun an other stars
	has definition thermonuclear reaction in which two protons collide a very high velocities and combine to form deuteurium, the deuteurium can capture a proton to form tritium and tritium can capture a proton to form helium
	has definition A series of thermonuclear reactions in which hydrogen nuclei are transformed into helium nuclei. The temperature and density required are about 107 K and 100 g cm-3. It is the main source of energy in the Sun, where 1038 of these reactions occur every second. All parts of this reaction have been observed in the laboratory, except for the first step 1H(p, β+v)2D, which occurs only a few times in 1012 collisions of protons. But the first two reactions provide about one-third of the Sun's total energy release. The p-p chain divides into three main branches: PP I, PP II and PP III.
	has definition Process of nuclear fusion by which relatively cooler stars produce and radiate energy; hotter stars commonly achieve the same result by means of the carbon-nitrogen cycle.
	has definition The nuclear sequence by which the Sun and all other main-sequence stars with less than 1.5 solar masses fuse hydrogen into helium.
	has definition An important nuclear fusion reaction that occurs in stars. It begins with the fusion of two hydrogen nuclei, each of which consists of a single proton.
	is a kind of hydrogen burning
	is a kind of pycnonuclear reaction
hydrogen burning	has minimum mass 0.08 solar masses
	has product helium
	has catalyst
	has reactant hydrogen
exothermic fusion process	liberates energy
fusion	has antonym fission
	produces energy
	has reaction probability
physical process	has domain physics

Kinds of proton-proton chain :

• pep reaction (3 facts) - A reaction occurring in the proton-proton chain which occurs only once in 400 p-p reactions but produces far more energetic neutrinos (1.44 MeV as against 0.42 MeV).
• PP I (3 facts) - A thermonuclear reaction in which hydrogen nuclei are transformed into helium nuclei producing 4 × 10^-5 ergs of energy. Although the neutrinos from this reaction are detectable, they have not been observed.
• PP II (3 facts) - A thermonuclear reaction in which hydrogen nuclei are transformed into helium nuclei. Although the neutrinos from this reaction are detectable, they have not been observed.
• PP III (4 facts) - A thermonuclear reaction in which hydrogen nuclei are transformed into helium nuclei. Occurs once in 1000 times.

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