In astrophysics and nuclear physics, the term is still quite common, and it typically means those three plus chromium and manganese—five elements that are exceptionally abundant, both on Earth and elsewhere in the universe, compared to their neighbors in the periodic table.
[8] Less common cations which are precipitated with the iron group include beryllium, titanium, zirconium, vanadium, uranium, thorium and cerium.
The explanation for this relative abundance can be found in the process of nucleosynthesis in certain stars, specifically those of about 8–11 Solar masses.
With no further source of energy to support itself, the core of the star collapses on itself while the outer regions are blown off in a Type II supernova.
In fact, there are several stable nuclides of elements from chromium to nickel around the top of the stability curve, accounting for their relative abundance in the universe.
Abundances of the chemical elements in the Solar System. The scale of the vertical axis is logarithmic. 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.
The curve of
binding energy
per
nucleon
(calculated from the nuclear
mass defect
) against the number of nucleons in the nucleus. Iron-56 is labelled near the very top of the curve: it can be seen that the "peak" is quite flat, which explains the existence of several common elements around iron.
