Carbon-12 Carbon-12 Carbon-12 (C) is the more abundant of the two stable isotopes of carbon (Carbon-13 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 masses of all nuclides are measured, thus, its atomic mass is exactly 12 daltons by definition. Its nucleus contains 6 protons and 6 neutrons. Before 1959 both the IUPAP and IUPAC used oxygen to define the mole; the chemists defining the mole as the number of
Isotopes of rutherfordium Isotopes of rutherfordium Rutherfordium (Rf) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was either Rf in 1966 or Rf in 1969. There are 16 known radioisotopes from Rf to Rf (3 of which, Rf, Rf, and Rf are unconfirmed) and 4 isomers. The longest-lived isotope is Rf with an estimated half-life of 5 hours. The longest directly measured half-life is Rf at 11 minutes, and the longest-lived isomer is Rf with a half-life of 81 seconds. Super-heavy elements such