slowing down fast neutrons so that Uranium fission continues by slow motion neutrons

accelerating fast neutrons

absorbing all neutrons

using moderator

fast moving

slow moving

critical neutrons

neutrons at rest

light weight atoms

heavy weight atoms

critical atoms

zero weight atoms

kinetic energy of neutrons

kinetic energy of fission products

instantaneous release of gamma rays

gradual radioactive decay of fission products

alpha particles

beta particles

thermal neutrons

fast neutrons and gamma rays