Atomic energy is a term used to describe the constitutive internal power of the atom, which was absorbed when formed.
Nuclear fusion reactors is a term used to describe a future source of energy. Most stars including our own Sun released energy by nuclear reactions between light atoms at temperatures of millions of degrees.
Neutron is an electrically neutral subatomic particle with a mass approximately equal to one atomic mass unit; generally found within an atomic nucleus.
Proton is a term used to describe a subatomic particle with a charge of +1 and a mass of approximately one atomic mass unit; generally found within an atomic nucleus.
Atom is a neutral particle having one nucleus, an unimaginably small particle that could not be made any smaller and still behaves as a chemical system.