C) is the more abundant of the two stable isotopes of carbon
being the other), amounting to 98.93% of the element carbon
; 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 mass
es of all nuclides
are measured, thus, its atomic mass is exactly 12 dalton
s by definition. Carbon-12 is composed of 6 protons
, 6 neutrons
, and 6 electrons
Before 1959, both the IUPAP
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 12 gram 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.
In 1980, the CIPM clarified the above definition, defining that the carbon-12 atoms are unbound and in their ground state
In 2018, IUPAC specified the mole as exactly 6.022 140 76 × 1023
"elementary entities". The number of moles in 12 grams of carbon-12 became a matter of experimental determination.
The Hoyle state is an excited, spinless, resonant state
of carbon-12. It is produced via the triple-alpha process
, and was predicted to exist by Fred Hoyle
The existence of the 7.7 MeV resonance Hoyle state is essential for the nucleosynthesis
of carbon in helium-burning red giant star
s, and predicts an amount of carbon production in a stellar environment which matches observations. The existence of the Hoyle state has been confirmed experimentally, but its precise properties are still being investigated.
The Hoyle state is populated when a helium-4
nucleus fuses with a beryllium-8
nucleus in a high-temperature (108 K
) environment with densely concentrated (105
) helium. This process must occur within 10−16
seconds as a consequence of the short half-life of 8
Be. The Hoyle state also is a short-lived resonance with a half-life of seconds; it primarily decays back into its three constituent alpha particle
s, though 0.0413(11)% of decays occur by internal conversion
into the ground state of 12
In 2011, an ab initio
calculation of the low-lying states of carbon-12 found (in addition to the ground
spin-2 state) a resonance with all of the properties of the Hoyle state.
The isotopes of carbon can be separated in the form of carbon dioxide
gas by cascaded chemical exchange reactions with amine carbamate
* Avogadro constant
* Isotopes of carbon
* Isotopically pure diamond
* Mole (unit)
Category:Isotopes of carbon