All atoms are made up of a heavy nucleus that contains protons (positively electrically charged particles) and neutrons (uncharged particles). The electrons are light negatively charged particles that orbit the nucleus. Neutrons that are by themselves can cause problems, because if a neutron is absorbed by a stable nucleus, the nucleus cans become unstable—or radioactive. In aneutronic fusion, NO neutrons are released, so NO radioactive waste is produced.
The structure of atoms, the basic constituents of people, animals, air, water and most things on earth, was discovered in the late 19th and early 20th century, as described in the websites below. (Atoms do not make up everything, contrary to the joke–”Why can’t you trust an atom?” In a plasma, the electrons and nuclei can be separated, so that atoms—consisting of electrons and nuclei, no longer exist, but their constituent parts still do.)
The Discovery of Atomic Structure: Resources
Marie Curie and The Discovery of Radioactivity:
Ernest Rutherford and The Discovery of the Nucleus: