Elements whose nuclei contain a total of 56 protons and neutrons (i.e. they have a mass number of 56), for example 56 Fe, 56 Ni, or 56 Co. Their formation by nuclear fusion inside a star marks the end-point of the star's energy output. Further fusion to create elements with higher mass numbers would absorb energy rather than liberate it. Nuclei of 62 Ni have the maximum binding energy, but those of 56 Fe have nearly the same binding energy and are more abundant as they are produced more readily in stellar nucleosynthesis.
Subjects: Astronomy and Astrophysics.