Nuclear energy comes in two varieties.
Fission
is the decay of heavy nuclei under the bombardment of "slow" neutrons.
Fusion
fuels the stars converting hydrogen into helium.
light, less massive elements
fuse
under stellar pressures.
heavy, more massive elements
fission
or break up.
fusion
fission
Strong force binds
Weak force decays
Einstein's Cosmos
Murray Gell-Mann
Atomic energy