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.
Captain Atom not mentioned in the panel in which they appear, but the Captain Atom is visually similar to Charlton's original version of the character. However, according to comments by Grant Morrison, this alternate universe is not the pre-Crisis Earth-4. 2007's "" features Captains Atom from alternate universes. The combatants of the series are introduced as a new Breach of Earth-8, a Ronnie Raymond/Nathaniel Adam fusion called "Quantum-Storm" from Earth-37, and another from Earth-38 who rules over his Atomic Knights. Additionally, issue #1 introduces a "Brigadier Atom" from Earth-13 married to Nightshade, and in "Countdown: Arena" #3, Breach gathers together a group