Proton -protthical chain – Wikipedia

The proton-protthical chain It is a nuclear chemical process that transforms hydrogen nuclei (protons) into helium nuclei. The process was hypothesized in 1939 by the German physicist and astronomer Hans Albrecht Bethe. The proton-professional cycle represents the source of main energy for most of the stars of the universe, including the sun in which this chain is the predominant process. Another process that leads to Elio’s formation starting from hydrogen is the CNO cycle.

In the first step, two hydrogen nuclei ^first H (protons) merge to form a nucleus of deuterio ² H, releasing a positron (since a proton has become a neutron) and a neutrino (β+decay).

^first H + ^first H → ² H + e ⁺ + n _{It is}

with the neutrino that brings an energy that varies from 0 to 0,42 MeV .

This first step is extremely slow for two reasons: the first is that for the two protons it is necessary to overcome the electrostatic repulsion barrier (and this can only take place due to tunnel effect, which has a low probability even if not nothing), and because the Decay from two protons to Deuterio is a weak interaction that converts a proton into a neutron. This is the bottleneck of the whole chain, a proton must wait for about 10 on average ⁹ years before merged with another to give a nucleus of deuterio.

The positron annihilates it immediately with an electron, and their resting masses are transformed into two gamma rays.

It is ⁺ + and ^– → 2γ for total energy of at least 1,022 Mev equal to the resting mass of the two particles

After the production of deuterio in the first step, it can be merged with another nucleus of hydrogen to produce a light isotope of the helium, the ³ He:

² H + ^first H → ³ He + γ + 5,49 mev

From here three different branches lead to the formation of the Isotoppy of Elio ⁴ He. In pp1 the Elio-4 comes from the merger of two Elio-3 nuclei; The other branches, PP2 and PP3 require Elio-4 produced in the PP1; Both have different paths that beryllium-7 can follow. In the sun, the PP1 branch has a frequency of 91%, pp2 9%and pp3 0.1%.

Ramo pp i [ change | Modifica Wikitesto ]

³ He + ³ He → ⁴ He + ^first H + ^first H + 12,96 MeV

The completion of the PP chain I releases a clear energy of 26.73 Mev.
The PP I branch is dominant at temperature between 10 and 14 mk. Under 10 mk, the PP chain no longer produces ⁴ He.

RAMO PP 2 [ change | Modifica Wikitesto ]

3 He + 4 He	→	7 Be + c
7 Be + e –	→	7 Li + ν It is
7 That + first H	→	4 He + 4 He

The PP II branch is dominant at temperatures between 14 and 23 mk.

90% of neutrinos produced in the reaction ⁷ Be(e ^– , n _{It is} ) ⁷ Li* bring an energy of 0.861 Mev, while the remaining 10% an energy of 0.383 Mev (it depends on the fact that lithium-7 is in an excited or not state).

Ramo PP 3 [ change | Modifica Wikitesto ]

3 He + 4 He	→	7 Be + c
7 Be + first H	→	8 B + c
8 B	→	8 Be + e + + n It is
8 Be	↔	4 He + 4 He

The pp III branch is dominant at temperatures greater than 23 mk.

The pp III branch is not the greater source of energy for the sun (since the nucleus temperature is not high quite high) but it is very important for the problem of solar neutrinos since it generates higher energy neutrinos (≤14.06 mev).

Ramo pp Iv it always [ change | Modifica Wikitesto ]

In this case the helium-3 reacts directly with a proton to give Elio-4

³ He + ^first H → ⁴ He + ν _{It is} + and ⁺

Energy released [ change | Modifica Wikitesto ]

Comparing the mass of the Elio-4 final with the masses of the four protons, it is obtained that 0.7% of the original mass is lost. This mass is converted into energy, in particular in gamma rays, in kinetic energy of the products and neutrinos released during individual reactions. The total energy obtained from an entire branch is 26.73 Mev.

Only the energy released in the form of gamma rays can interact with electrons and protons and heat the inside of the sun. This heating means that the sun does not collapse under its weight.

Deuterio can also be produced through a rare PEP electronic capture reaction (proton-electron-protrone):

^first H + e ^– + ^first H → ² H + n _{It is}

In the sun, the frequency of the PEP reaction is 1/400 of the pp. However, the neutrinos released are much more energetic: while the neutrinos produced in the first passage of the PP range from 0 to 0.42 Mev, the PEP neutrinos produce a narrow line at 1.44 Mev.