Iron peak

The iron peak is a local maximum in the vicinity of Fe (V, Cr, Mn, Fe, Co and Ni) on the graph of the abundances of chemical elements, as seen below.

For elements before iron, nuclear fusion releases energy. For elements heavier than iron, nuclear fusion consumes energy, but nuclear fission releases it. Chemical elements up to the iron peak are produced in ordinary stellar nucleosynthesis. Heavier elements are produced only during supernova nucleosynthesis. This is why we have more iron peak elements than in its neighbourhood.

Abundances of the chemical elements in the Solar system. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesized in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers, and (2) a general decrease in abundance, as elements become heavier. The "iron peak" may be seen in the elements near iron as a secondary effect, increasing relative abundances of elements with nuclei most strongly bound.

Binding energy

The graph below shows the binding energy of various elements. Increasing values of binding energy can be thought of in two ways:

1. It is the energy required to remove a nucleon from a nucleus; and
2. It is the energy released when a nucleon is added to a nucleus.

As can be seen, light elements such as hydrogen release large amounts of energy (a big increase in binding energy) as nucleons are added—the process of fusion. Conversely, heavy elements such as uranium release energy when nucleons are removed—the process of nuclear fission. Although nuclei with 58 and 62 nucleons have the very highest binding energy, fusing four nucleons to nickel–56 to produce the next element — zinc–60 — actually requires energy rather than releasing any. Accordingly, nickel–56 is the last fusion product produced in the cores of high-mass stars (see also Silicon burning process).

See also

• Abundances of the elements (data page)