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.
A Is for Atom A Is for Atom A Is for Atom is a 14-minute 1953 promotional animated short documentary film created by John Sutherland and sponsored by General Electric (GE). It is now in the public domain. The short explains what an atom is, how nuclear energy is released from certain kinds of atoms, the peacetime uses of nuclear power, and the by-products of nuclear fission. It is Sutherland's most-decorated film, having won numerous honors at film festivals. "A is for Atom" was re-released by General Electric in 1964. John Sutherland Studios was contracted by GE to modernize the film. Changes include included