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Nukleosintesis Big Bang
[[Nukleosintesis Big Bang]] terjadi pada tiga menit pertama penciptaan alam semesta dan bertanggung jawab atas banyak perbandingan kelimpahan <sup>1</sup>H ([[atom hidrogen|protium]]), <sup>2</sup>H ([[deuterium]]), <sup>3</sup>He ([[helium-3]]), dan <sup>4</sup>He ([[helium-4]]), di alam semesta<ref>{{dead link|url=http://www.astro.washington.edu/research/bbn/|date=March 2009}} Big Bang Java Calculator v1.1, Craig Hogan, Luis Mendoza</ref>.
 
Meskipun <sup>4</sup>He terus saja dihasilkan oleh mekanisme lainnya (seperti fusi bintang dan peluruhan alfa) dan jumlah jejak <sup>1</sup>H terus saja dihasilkan oleh [[spalasi]] dan jenis-jenis khusus peluruhan radioaktif ([[pelepasan proton]] dan [[pelepasan neutron]]), sebagian besar massa isotop-isotop ini di alam semesta, dan semua kecuali jejak-jejak yang tidak signifikan dari <sup>3</sup>He dan deuterium di alam semesta yang dihasilkan oleh proses langka seperti [[peluruhan kluster]], dianggap dihasilkan di dalam proses [[Big Bang]].
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Although <sup>4</sup>He continues to be produced by other mechanisms (such as stellar fusion and alpha decay) and trace amounts of <sup>1</sup>H continue to be produced by [[spallation]] and certain types of radioactive decay ([[proton emission]] and [[neutron emission]]), most of the mass of these isotopes in the universe, and all but the insignificant traces of the <sup>3</sup>He and deuterium in the universe produced by rare processes such as [[cluster decay]], are thought to have been produced in the [[Big Bang]]. The nuclei of these elements, along with some <sup>7</sup>Li, and <sup>7</sup>Be are believed to have been formed when the universe was between 100 and 300 seconds old, after the primordial [[quark]]-[[gluon]] plasma froze out to form [[proton]]s and [[neutron]]s. Because of the very short period in which Big Bang nucleosynthesis occurred before being stopped by expansion and cooling, no elements heavier than [[lithium]] could be formed. (Elements formed during this time were in the plasma state, and did not cool to the state of neutral atoms until much later).
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