Fission and Fusion
Can any atom undergo fission or fusion??
how is it that both fission and fusion release energy??
Here's an approximate rule of thumb: Fusion releases energy when the
product is lower than around iron in the periodic chart. Fission
releases energy when the precursor is higher than around iron. The
root cause of this is that the electrostatic force is long range while
the nuclear force is short range, so repulsion between protons becomes
increasingly important as the nucleus gets larger.
This is why stars blow up, by the way. They fuse stuff until they
make iron, and then they get upset when it no longer works.
Yes, any atom may undergo fission or fusion, but either or both processes
may require energy. It's all a matter of energetics: if the initial atom
is lower in energy that the final products, the process will require energy.
If the initial atom is higher in energy than the final products, the process
will release energy.
Generally, it is fission of the heavy elements and fusion of the light
elements that release energy. This is because the most stable nuclei have
intermediate weights: iron is about as good as it gets. Other very stable
nuclei include carbon-12 and helium-4. Other considerations for other types
of radioactive decay include the proton/neutron ratio of the nucleus and the
internal energy state of the nucleus.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
Click here to return to the Physics Archives
Update: June 2012