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 incarnations, he is Air Force pilot Nathaniel Adam, who was used as a test subject in a scientific experiment and wound up seemingly disintegrated in the process, only to reappear later as Captain Atom, now blessed with superhuman abilities. Over the years, DC has attempted to reinvent the character a number of times. For a period, the character assumed the mantle of the supervillain Monarch, and in 2005 DC attempted to retell the Captain Atom story with an entirely new character, Breach, who was subsequently discarded. In the new continuity following DC's 2011 relaunch, Captain Atom has never been a