In terms of fission
, a nuclear chain reaction
is a continuous
splitting of atoms
capable of sustaining such a reaction include U-235
, and some others.
Basically, you fire a stream of neutrons
into one of those materials. The neutrons collide
with individual atoms, splitting them and releasing more neutrons. If the material is dense
enough, those neutrons go on to split more atoms, and so on. Thus, the reaction sustains itself.
a neutron is travelling, the less likely it will hit an atom, thus most nuclear chain reactions take place in a hydrogen
, as hydrogen has a slowing effect on neutrons.
Reactions that are intended to have a rapid, devastating effect require little in the way of control
. See atomic bomb
. Otherwise, the chain reaction can be controlled by way of addition or removal of cadmium, which absorbs neutrons. The control rods
present in all nuclear reactors are made of cadmium