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Article: Carbon-12


History of Carbon-12

  • Before 1959, IUPAP and IUPAC used oxygen to define the mole.
  • In 1959-60, the two organizations agreed to define the mole as the number of atoms in 12 grams of carbon-12.
  • The definition of the mole was adopted by the CIPM in 1967 and by the 14th CGPM in 1971.
  • In 1961, carbon-12 was selected as the standard relative to which the atomic weights of all other elements are measured.
  • In 1980, the CIPM clarified that the carbon-12 atoms are unbound and in their ground state.

Hoyle State of Carbon-12

  • The Hoyle state is an excited, spinless, resonant state of carbon-12.
  • It was predicted to exist by Fred Hoyle in 1954.
  • The existence of the Hoyle state is essential for the nucleosynthesis of carbon in helium-burning stars.
  • The Hoyle state is populated when a helium-4 nucleus fuses with a beryllium-8 nucleus in a high-temperature environment.
  • The Hoyle state primarily decays back into its three constituent alpha particles.

Isotopic Purification of Carbon-12

  • Isotopes of carbon can be separated in the form of carbon dioxide gas.
  • This can be done through cascaded chemical exchange reactions with amine carbamate.
  • Isotopic purification is important for various applications, such as scientific research and medical diagnostics.
  • It allows for the study of specific isotopes and their properties.
  • Isotopically pure carbon can also be used in the production of materials like diamond.

Related Concepts

  • Avogadro constant
  • Carbon-11
  • Carbon-13
  • Carbon-14
  • Isotopes of carbon


  • Table of Isotopic Masses and Natural Abundances (PDF). 1999.
  • Atomic Weights and the International Committee — A Historical Review. 2004-01-26.
  • Hoyle, F. (1954). On Nuclear Reactions Occurring in Very Hot Stars.
  • Freer, M.; Fynbo, H. O. U. (2014). The Hoyle state in C.
  • Alshahrani, B.; Kibédi, T.; Stuchberry, A. E.; Williams, E.; Fares, S. (2013). Measurement of the radiative branching ratio for the Hoyle state using cascade gamma decays.

Carbon-12 Data Sources

Reference URL
Knowledge Graph

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