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The proton–proton chain reaction is one of two nuclear fusion reactions, along with the CNO cycle, by which stars convert hydrogen to helium and which dominates in stars the size of the Sun or smaller.〔(The Proton-Proton Chain )〕 In general, proton–proton fusion can occur only if the temperature (i.e. kinetic energy) of the protons is high enough to overcome their mutual electrostatic or Coulomb repulsion.〔Ishfaq Ahmad, ''The Nucleus'', 1:42,59, (1971), The Proton type-nuclear fission reaction〕 In the Sun, deuterium-producing events are rare as diprotons, the much more common result of nuclear reactions within the star, immediately decay back into two protons. A complete conversion of the hydrogen in the solar core is calculated to take more than (ten billion) years.〔Kenneth S. Krane, ''Introductory Nuclear Physics'' , Wiley , 1987, p. 537.〕 ==History of the theory== The theory that proton–proton reactions are the basic principle by which the Sun and other stars burn was advocated by Arthur Stanley Eddington in the 1920s. At the time, the temperature of the Sun was considered too low to overcome the Coulomb barrier. After the development of quantum mechanics, it was discovered that tunneling of the wavefunctions of the protons through the repulsive barrier allows for fusion at a lower temperature than the classical prediction. Even so, it was unclear how proton–proton fusion might proceed, because the most obvious product, helium-2 (diproton), is unstable and immediately dissociates back into a pair of protons. In 1939, Hans Bethe proposed that one of the protons could beta decay into a neutron via the weak interaction during the brief moment of fusion, making deuterium the initial product in the chain.〔Hans A. Bethe, ''Physical Review'' 55:103, 434 (1939); cited in Donald D. Clayton, ''Principles of Stellar Evolution and Nucleosynthesis'', The University of Chicago Press, 1983, p. 366.〕 This idea was part of the body of work in stellar nucleosynthesis for which Bethe won the 1967 Nobel Prize in Physics. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Proton–proton chain reaction」の詳細全文を読む スポンサード リンク
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