iron peak

The iron peak is a peak on the graph relating element abundances to atomic numbers. The peak is centered around iron (atomic number 26) and shows high abundances of some elements with atomic numbers close to iron's (iron peak elements). The peak is theorized to result from these elements' high stability (iron's being the highest) due to their high binding energy, along with the fact that nuclei are synthesized by step-wise enlargement (e.g., the alpha process), and iron's high stability allows fewer nuclei to progress further toward even heavier elements, which are somewhat less stable. Another way to state this is that beyond iron's atomic number, the nucleosynthesis reaction stepping up from iron, as well as many further reactions toward heavier nuclei, are endothermic, i.e., the reactions absorb energy rather than release some, reducing the occasions when sufficient energy is present to produce such reactions, as well as working against further temperature increase.