Editing Hadean Eon (section)

===== Fusion - Step 1 =====
When two protons come very close, one of the protons can (very rarely; one in a billion such interactions) undergo a weak nuclear reaction, where it transforms into a '''neutron'''. This transformation is mediated by the <u>weak nuclear force</u>, which operates at very short ranges and is responsible for processes like '''radioactive decay'''. The emergent neutron can then pair with the remaining proton to form '''deuterium''' (<sup>2</sup>H), a hydrogen '''isotope''' with one proton and one neutron in its nucleus. The remaining '''proton''' (p<sup>+</sup>) fuses with its decayed neutron partner, forming a new '''deuterium''' nucleus (<sup>2</sup>H), but also releasing a '''positron''' (e<sup>+</sup>), and a '''neutrino''' (ν<sub>e</sub>).   

* '''1p<sup>+</sup> + [1p<sup>+</sup>→n + (W+→e<sup>+</sup> + ν<sub>e</sub>)]'''<sub>The proton becomes a neutron, releasing a W+ boson (which quickly becomes a positron and a neutrino).</sub> 
* '''p<sup>+</sup> + n → <sup>2</sup>H + e<sup>+</sup> + ν<sub>e</sub>'''<sub>The proton and the neutron fuse, creating a new deuterium nucleus; the positron and neutrino remain.</sub>

Both protons and neutrons are '''nucleons''' (components of atomic nuclei); a proton has a positive electric charge, while a neutron has no '''electric charge'''. Despite this difference, protons and neutrons are quite similar in mass and are both '''fermions''', meaning that they both follow the <u>Pauli exclusion principle</u>. 

The transformation from a proton to a neutron changes the type (or '''flavor''') of one of the nucleon's fundamental particles, called '''quarks'''. The proton (composed of two '''up quarks''' and one '''down quark''') transforms into a neutron (composed of one up quark and two down quarks) through this process, an example of beta-plus decay ('''β+ decay'''). This transformation emits a '''W+ boson''' (a carrier particle of the <u>weak nuclear force</u>), which then quickly decays into a positron (e<sup>+</sup>) and an electron neutrino (ν<sub>e</sub>). In the transformation, '''charge conservation''' is maintained; the initial positive charge of the proton is balanced by the creation of a '''positron''', which carries a positive charge, ensuring that the total charge before and after the reaction remains constant.