Atom of Ernest Rutherford, bombarded a metal foil with alpha particles to observe how they scattered. They expected all the alpha particles to pass straight through with little deflection, because Thomson's model said that the charges in the atom are so diffuse that their electric fields could not affect the alpha particles much. However, Geiger and Marsden spotted alpha particles being deflected by angles greater than 90°, which was supposed to be impossible according to Thomson's model. To explain this, Rutherford proposed that the positive charge of the atom is concentrated in a tiny nucleus at the center of the atom.
Captain Atom of alternate Captains Atom, including Earth-13's Brigadier, the Captain Atom as depicted in the graphic novel "Kingdom Come" (Earth-22), and a Captain in a red/silver variant of the Monarch's costume, one similar to the Charlton Comics Atom (Earth-4), and a Hulked out variant named Attum from an unknown Earth. Several more variants are shown in "Countdown: Arena" #4, including a President Atom, a robot called Quantum Mechanix, Kid Quantum of the Legion of Super-Heroes, Captain Adamma, Quantum Boy, an anthropomorphic wolf version, a from Earth-30, a Doctor Manhattan-lookalike, an energy based-Atom who makes calculations during his attacks, and a giant-sized