B What is the heaviest element that a star will fuse?

Nickel 56 decays into cobalt, then iron.

 

The half lives are both relatively short ( < 7 days, < 80 days). Whether energy/density conditions in a stellar core modify this, I am not sure. Since iron-56 makes up a large majority of planetary iron, I assume most comes from decay of nickel 56 produced in stars.

 

The star kills itself when it creates iron, after which it creates many of the heavier elements when it goes supernova; search up 'r-process'.

 

http://www.physics.smu.edu/scalise/quarknet2008/FewellAJP000653.pdf
Page 656
Seems like mostly iron in the core. A higher temperature is need to produce nickel, but then that higher temperature disintegrates iron faster than nickel production.
Comments?

 

Enormous energy is needed to fuse iron or any heavier elements - hence most are formed by supernovae which do have sufficient energy for such processes.

 

Get a chart of isotopic masses and relative abundances, like

https://www.ncsu.edu/chemistry/msf/pdf/IsotopicMass_NaturalAbundance.pdf

and you can work it out for yourself. For example, a star fuses 4 atoms of hydrogen 1, 4 times 1.007825 = 4.0323
to get 1 atom of Helium 4, mass 4.002603, and releases
4.0323 -4.002603 = 0.029697 units of energy.

Try fusing 1 atom of hydrogen 1, 1.007825, to 1 unit of Iron 56, 55.934942
to get Iron 57 with mass of 56.935399, and the star releases
1.007825 + 55.934943 - 56.935399= 0.0073681 units of energy.

Try fusing 1 atom of carbon 12, 12..00000 , to 1 unit of Iron 56, 55.934942
to get zinc 68, and the star gets
12.0000 +55.934942 - 67.924848= minus 0. 01.0094 units of energy.

If there were still hydrogen in the core, a star could still gain a little energy by fusing Iron and Hydrogen to get NIckel, but by the time Iron has formed, there's a negligible amount of unfused Hydrogen left in the core. All the minus unit energy elements are produced only in a supernova.