56Fe

56Fe is an isotope of iron with a mass number of 56 and atomic number 26. It is the most abundant iron isotope in nature and one of the most common isotopes in the universe. The atomic mass of 56Fe is about 55.9349 atomic mass units. The nucleus has a ground-state spin of 0+ and is stable, with no radioactive decay under normal conditions.

In terms of nuclear properties, 56Fe lies near the peak of the binding-energy curve, with a binding energy per nucleon of about 8.8 MeV. This high binding energy makes 56Fe one of the most tightly bound nuclei, yielding a total binding energy of roughly 490–492 MeV. The stability and high binding energy explain why energy is released during fusion of lighter nuclei up to iron, but fusion of iron or heavier elements does not produce net energy.

Natural abundances show 56Fe as the dominant iron isotope. In terrestrial iron, approximately 92% of atoms are 56Fe, with smaller fractions of 54Fe, 57Fe, and 58Fe. In the solar system, the same pattern holds, making 56Fe the principal iron isotope in most rocks and meteorites.

Astrophysical significance centers on nucleosynthesis in stars. 56Fe is produced in the late stages of massive-star evolution, notably during silicon burning, and in explosive nucleosynthesis in core-collapse and Type Ia supernovae. A related process involves the production of 56Ni, which decays to 56Co and then to 56Fe, providing a major energy source that powers supernova light curves.

56Fe is a stable, non-radioactive isotope and serves as the primary constituent of celestial and terrestrial iron, underpinning both geochemical studies and models of stellar evolution.