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 stability allows fewer nuclei to progress further toward even heavier elements. Another way to state this is that beyond iron's atomic number, nucleosynthesis reactions toward heavier nuclei are generally endothermic, i.e., they absorb energy and are less probable.