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Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in a process called Big Bang nucleosynthesis. [1]
Finally, there is a very low density of baryons (neutrons and protons). The BBN model follows the nuclear reactions of these baryons as the temperature and pressure drops due to expansion of the universe. [3]: 62 The basic model makes two simplifying assumptions: until the temperature drops below 0.1 MeV only neutrons and protons are stable and
This creates a helium-4 nucleus through a sequence of reactions that begin with the fusion of two protons to form a deuterium nucleus (one proton plus one neutron) along with an ejected positron and neutrino. [22] In each complete fusion cycle, the proton–proton chain reaction releases about 26.2 MeV. [22]
Reactions with neutrons are important in nuclear reactors and nuclear weapons. While the best-known neutron reactions are neutron scattering, neutron capture, and nuclear fission, for some light nuclei (especially odd-odd nuclei) the most probable reaction with a thermal neutron is a transfer reaction:
Between about 2 and 20 minutes after the Big Bang nuclear fusion reactions convert a 1/7 mixture of neutrons and protons in to a mix of protons, deuterium (a proton fused with a neutron), 3 He, 4 He, with trace amounts of 7 Li and 7 Be. These reactions end when the temperature falls below the 0.07MeV needed for nuclear fusion.
About 99% of the energy output of the sun comes from the various p–p chains, with the other 1% coming from the CNO cycle. According to one model of the sun, 83.3 percent of the 4 He produced by the various p–p branches is produced via branch I while p–p II produces 16.68 percent and p–p III 0.02 percent. [1]
Just before 7 a.m. on Dec. 24, the Parker Solar Probe passed within just 3.8 million miles of the sun’s surface — seven times closer to the burning ball of gas than any other mission has ...
Free protons of high energy and velocity make up 90% of cosmic rays, which propagate through the interstellar medium. [33] Free protons are emitted directly from atomic nuclei in some rare types of radioactive decay. [34] Protons also result (along with electrons and antineutrinos) from the radioactive decay of free neutrons, which are unstable ...