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The stability of helium-4 is the reason that hydrogen is converted to helium-4, and not deuterium (hydrogen-2) or helium-3 or other heavier elements during fusion reactions in the Sun. It is also partly responsible for the alpha particle being by far the most common type of baryonic particle to be ejected from an atomic nucleus; in other words ...
One analogy is to think of helium-4 as ash, and the amount of ash that one forms when one completely burns a piece of wood is insensitive to how one burns it. The resort to the BBN theory of the helium-4 abundance is necessary as there is far more helium-4 in the universe than can be explained by stellar nucleosynthesis. In addition, it ...
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]
The Oddo–Harkins rule for elements from 12 C to 56 Fe is explained by the alpha process of stellar nucleosynthesis. [6]: 42 The process involves the fusion of alpha particles (helium-4 nuclei) under high temperature and pressure within the stellar environment. Each step in the alpha process adds two protons (and two neutrons), favoring ...
Illustration of a proton–proton chain, from hydrogen forming deuterium, helium-3, and regular helium-4. Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. [1] Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.
As a side effect of the process, some carbon nuclei fuse with additional helium to produce a stable isotope of oxygen and energy: 12 6 C + 4 2 He → 16 8 O + γ (+7.162 MeV) Nuclear fusion reactions of helium with hydrogen produces lithium-5, which also is highly unstable, and decays back into smaller nuclei with a half-life of 3.7 × 10 −22 s.
Once the helium-3 has been produced, there are four possible paths to generate 4 He. In p–p I, helium-4 is produced by fusing two helium-3 nuclei; the p–p II and p–p III branches fuse 3 He with pre-existing 4 He to form beryllium-7, which undergoes further reactions to produce two helium-4 nuclei. About 99% of the energy output of the sun ...
The end product is one alpha particle (a stable helium nucleus), two positrons, and two electron neutrinos. There are various alternative paths and catalysts involved in the CNO cycles, but all these cycles have the same net result: 4 1 1 H + 2 e − → 4 2 He + 2 e + + 2 e − + 2 ν e + 3 γ + 24.7 MeV → 4 2 He
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