NEUTRONIO As we said yesterday: 1 . In the scientific field, neutronium is the residual nucleus of a neutron star that has released its neutrons leaving a very dense mass. 2 . Before the discovery of the neutron the German chemist Andreas von Antropoff invented in 1926 the term neutronium, also called "element zero", to refer to a theoretical substance consisting only of neutrons, ? that is, a chemical element without protons, which would therefore occupy the atomic number zero in the periodic table of the elements.