Atom bombardment ejects what appeared to be hydrogen nuclei. By 1920 he had accepted that the hydrogen nucleus is a distinct particle within the atom and named it proton. Neutrons have no electrical charge and have a free mass of 1,839 times the mass of the electron, or , the heaviest of the three constituent particles, but it can be reduced by the nuclear binding energy. Neutrons and protons (collectively known as nucleons) have comparable dimensions—on the order of —although the 'surface' of these particles is not sharply defined. The neutron was discovered in 1932 by the English physicist James Chadwick.
Mister Atom long, however: In "52", Captain Marvel mentioned that Mister Atom attacked the Rock of Eternity, only to fail. It is later revealed that Mister Atom is one of the villains who helped Prometheus plant explosive devices in various cities across the U.S., which leads to Mister Atom and several other villains making an attempt to flee the country. Before they can cross the border, the group is attacked by the Justice League, and Mister Atom is defeated and captured by Starman and Congorilla. Mister Atom has upper level superhuman strength and endurance. His robot body is virtually impervious to harm.