After a star completes the oxygen burning process, its core is composed primarily of silicon and sulfur.If it has sufficiently high mass, it further contracts until its core reaches temperatures in the range of 2.7–3.5 GK (230–300 ke V).Stars with initial masses less than about eight times the sun never develop a core large enough to collapse and they eventually lose their atmospheres to become white dwarfs.
The central portion of the star is now crushed into either a neutron star or, if the star is massive enough, a black hole.
Those fusion reactions create the elements silicon, sulfur, chlorine, argon, sodium, potassium, calcium, scandium, titanium and iron peak elements: vanadium, chromium, manganese, iron, cobalt, and nickel.
These are called "primary elements", in that they can be fused from pure hydrogen and helium in massive stars.
This isotope undergoes radioactive decay into iron-56, which has one of the highest binding energies of all of the isotopes, and is the last element that produces a net release of energy by nuclear fusion, exothermically.
All nuclear fusion reactions that produce heavier elements cause the star to lose energy and are said to be endothermic reactions.