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Carbon-12 is the more abundant carbon of the two stable isotopes, amounting to 98.93% of the element carbon;〔(【引用サイトリンク】title=Table of Isotopic Masses and Natural Abundances )〕 its abundance is due to the triple-alpha process by which it is created in stars. Carbon-12 is of particular importance in its use as the standard from which atomic masses of all nuclides are measured: its mass number is 12 by definition and contains 6 protons, 6 neutrons and 6 electrons. == History == Prior to 1959 both the IUPAP and IUPAC used oxygen to define the mole; the chemists defining the mole as the number of atoms of oxygen which had mass 16 g, the physicists using a similar definition but with the oxygen-16 isotope only. The two organizations agreed in 1959/60 to define the mole as follows. The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol." This was adopted by the CIPM (International Committee for Weights and Measures) in 1967, and in 1971 it was adopted by the 14th CGPM (General Conference on Weights and Measures). In 1961 the isotope carbon-12 was selected to replace oxygen as the standard relative to which the atomic weights of all the other elements are measured.〔(【引用サイトリンク】title=Atomic Weights and the International Committee — A Historical Review )〕 In 1980 the CIPM clarified the above definition, defining that the carbon-12 atoms are unbound and in their ground state. 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「Carbon-12」の詳細全文を読む スポンサード リンク
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