From the March 2010 issue

My astronomy book reads, “Heavy-element fusion in massive stars ends with iron.” How are elements heavier than iron in the periodic table created?

Kate Jenks, Lexington, Virginia
By | Published: March 29, 2010 | Last updated on May 18, 2023
May 2010 heavy elements
In certain environments (such as a supernova), an iron nucleus can capture neutrons. Eventually, one of those neutrons will convert into a proton, an electron, and an antineutrino. This process, called “neutron capture,” then changes the iron nucleus (26 protons) to a cobalt nucleus (27 protons). These events repeat to create heavier elements.
Astronomy: Roen Kelly

In an environment packed with excess energy (like a supernova), a small fraction of this energy may be used to bind free neutrons to iron atoms. One of the neutrons in the nucleus decays (or changes) into a proton, and the nucleus’s charge increases by one to produce a heavier element.