Chain proton-proton

The chain proton-proton , so known under the name of chain PP is one of the two reactions of nuclear Fusion by which the star S convert Hydrogène into Hélium; other reaction being the Cycle carbon-nitrogenize-oxygen. The chain proton-proton is more important in stars of mass relatively low, like the Sun or less.

The chain proton-proton

The first stage implies the fusion of two cores of hydrogen 1 H, or Proton S in Deuterium 2 H with emission of a Positron, one of the protons being changed into Neutron, and of a Neutrino. To overcome the electrostatic repulsion between the two hydrogen cores requires a great quantity of energy and this reaction takes on average 10 billion years to achieve itself. It is because of the slowness of this reaction that the sun is always shining; if it were faster, the sun would have exhausted its hydrogen a long ago.

The number of neutrinos detected coming from the sun is significantly in lower part of what theoretical calculations provide for the chain proton-proton; it is the Problème of the solar neutrinos. The observations of the waves of Pressure in the Sun, the Hélioséismologie, indicated that the pressures and the temperatures in the sun are very close to the pressures and the temperatures envisaged by the theory; what tends to confirm that our comprehension of the chain of proton-proton is correct. This carried out astrophysicists to believe that the problem of the solar neutrinos comes from the unexpected behavior of the neutrinos after they are produced.

1 H + 1 H → 2 H + E + + ν {{ind|E}} +: 0.42 MeV

The positron is destroyed immediately with one of the electron S of an atom of hydrogen and their mass-energy is evacuated in the form of two Photon S gamma.

E + + E - → 2 γ +: 1.02 MeV

After this, deuterium produced at the time of the first stage can amalgamate with a new hydrogen core to produce a Isotope Hélium 3 He:

2 H + 1 H → 3 He + γ +: 5.49 MeV

Finally, after million years, two helium cores 3 He can amalgamate and produce the normal isotope of helium 4 He as two hydrogen cores which can begin the reaction of three again way various called PP1, PP2 and PP3:

PP1

3 He + 3 He → 4 He + 1 H + 1 H +: 12.86 MeV

Total reaction PP1 produces a clear quantity of energy of: 26.7 MeV. Chain PP1 is dominant has temperatures of 10-14 million Kelvin. In lower part of 10 million Kelvin, the PP chain does not produce much of 4 He.

PP2

Chain PP2 is dominant at temperatures of order 14-23 million Kelvin.

PP3

Chain PP3 is dominant if the temperature exceeds 23 million Kelvin. This chain is not the primary source of energy in the Sun, but it is very important for the problem of the solar neutrinos because it generates the energy neutrinos.

In general, fusion proton-proton can take place only if the temperature (the kinetic energy) of the protons is enough high to be able to overcome their Coulomb repulsion mutual insurance companies. The theory according to which the reactions of the chain proton-proton are the basic principle of energy production of stars was advanced by Arthur Eddington in the Années 1920. At that time, the temperature of the Sun was regarded as too weak surmounting the Coulomb barrier; but after the development of the quantum Mechanical , one discovered that the Tunnel effect made it possible the protons to cross this barrier at a temperature lower than that predicted by the traditional Mécanique.

See too

Reaction triple-alpha

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