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 seaborgium Isotopes of seaborgium Seaborgium <nowiki>(</nowiki>Sg) 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 Sg in 1974. There are 12 known radioisotopes from Sg to Sg and 2 known isomers (Sg and Sg). The longest-lived isotope is Sg with a half-life of 3.1 minutes. "This section deals with the synthesis of nuclei of seaborgium by so-called "cold" fusion reactions. These are processes that create compound nuclei at low excitation energy (~10–20 MeV, hence "cold"), leading to a higher probability of